Dentin bonding agents- GUIDED BYDR SUNANDA GADDALAYDR ANITA KALEDR YOGESH AHIRRAODR HRISHIKESH GHULEDR ARCHANA DAGADR NANDINI BIRADAR

By Sneha RatnaniMds part 1

Introduction Principles of adhesion Indications for Use of Adhesives Advantages of Bonding Techniques Mechanisms of adhesion Factors affecting adhesion Challenges in adhesion Dentin bonding systems Evolution of bonding agents Classification of bonding agents Conclusion References

Contents

The dental profession has spent most of its history restoring the effects of dental disease but currently the majority of restoration work is replacement or repair of prior treatment

One reason for the change is populationrsquos burgeoning interest in health and beauty which is driving increased demand for cosmetic dental procedures

Historically for many adults the achievement of a pretty smile has meant submission to extensive invasive procedures and high-cost fixed prosthodontics

Improvements in tooth-colored restoratives and bonding technology have made cosmetic dental procedures more palatable and feasible

In addition newer technology allows the general practitioner to handle many previously complex esthetic problems more simply conservatively and economically

Introduction

The fundamental objective of all restorations since centuries has been to create adhesion between two dissimilar surfaces mineralized tooth structure and the restorative materials

The invention of dentin bonding agent is like a - dream come true for dentistry which led to the beginning of new era of adhesive dentistry

The concept of dentistry with the introduction of adhesives has changed from - Extension for Prevention to PREVENTION OF EXTENSION

Introduction

The principles of adhesive dentistry dates back to 1955 when buonocore after observing industrial use of phosphoric acid to improve adhesion of paints and resin coatings to metal surfaces applied acid to the teeth to lsquorender the tooth surface more receptive to adhesionrsquo

Michael Buonocore

The traditional ldquodrill and fillrdquo approach is fading now because of numerous advancements taking place in restorative dentistry

ADHESIVE DENTISTRY

Adhesion The state in which two surfaces are held together by interfacial forces

which may consists of valence forces or interlocking forces or both (The American Society for Testing and Materials specification D 907)

Adherend The surface or substrate that is adhered

Adhesiveadherent A material that can join substances together resist separation and transmit loads across the bond

Adhesive failure The bond that fails at the interface between the two substrates

Cohesive failure The bond fails within one of the substrates but not at the interface

PRINCIPLES OF ADHESION

Adherend 1 Adherend 2

Adhesive Systemor Luting Cement

Interface 2Interface 1

DENTALJOINT

ENAMEL DENTIN gtLiner Base Cement gt

Post and Core gtDental Amalgam gt

Implant gt

lt Composite Amalgamlt Cast Inlay Onlay or Crownlt All-Ceramic Inlay Onlay or Crownlt Veneers Maryland Bridgeslt Orthodontic Brackets

AdhesiveInterface 1 DENTALADHESION

>

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Introduction Principles of adhesion Indications for Use of Adhesives Advantages of Bonding Techniques Mechanisms of adhesion Factors affecting adhesion Challenges in adhesion Dentin bonding systems Evolution of bonding agents Classification of bonding agents Conclusion References

Contents

The dental profession has spent most of its history restoring the effects of dental disease but currently the majority of restoration work is replacement or repair of prior treatment

One reason for the change is populationrsquos burgeoning interest in health and beauty which is driving increased demand for cosmetic dental procedures

Historically for many adults the achievement of a pretty smile has meant submission to extensive invasive procedures and high-cost fixed prosthodontics

Improvements in tooth-colored restoratives and bonding technology have made cosmetic dental procedures more palatable and feasible

In addition newer technology allows the general practitioner to handle many previously complex esthetic problems more simply conservatively and economically

Introduction

The fundamental objective of all restorations since centuries has been to create adhesion between two dissimilar surfaces mineralized tooth structure and the restorative materials

The invention of dentin bonding agent is like a - dream come true for dentistry which led to the beginning of new era of adhesive dentistry

The concept of dentistry with the introduction of adhesives has changed from - Extension for Prevention to PREVENTION OF EXTENSION

Introduction

The principles of adhesive dentistry dates back to 1955 when buonocore after observing industrial use of phosphoric acid to improve adhesion of paints and resin coatings to metal surfaces applied acid to the teeth to lsquorender the tooth surface more receptive to adhesionrsquo

Michael Buonocore

The traditional ldquodrill and fillrdquo approach is fading now because of numerous advancements taking place in restorative dentistry

ADHESIVE DENTISTRY

Adhesion The state in which two surfaces are held together by interfacial forces

which may consists of valence forces or interlocking forces or both (The American Society for Testing and Materials specification D 907)

Adherend The surface or substrate that is adhered

Adhesiveadherent A material that can join substances together resist separation and transmit loads across the bond

Adhesive failure The bond that fails at the interface between the two substrates

Cohesive failure The bond fails within one of the substrates but not at the interface

PRINCIPLES OF ADHESION

Adherend 1 Adherend 2

Adhesive Systemor Luting Cement

Interface 2Interface 1

DENTALJOINT

ENAMEL DENTIN gtLiner Base Cement gt

Post and Core gtDental Amalgam gt

Implant gt

lt Composite Amalgamlt Cast Inlay Onlay or Crownlt All-Ceramic Inlay Onlay or Crownlt Veneers Maryland Bridgeslt Orthodontic Brackets

AdhesiveInterface 1 DENTALADHESION

>

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The dental profession has spent most of its history restoring the effects of dental disease but currently the majority of restoration work is replacement or repair of prior treatment

One reason for the change is populationrsquos burgeoning interest in health and beauty which is driving increased demand for cosmetic dental procedures

Historically for many adults the achievement of a pretty smile has meant submission to extensive invasive procedures and high-cost fixed prosthodontics

Improvements in tooth-colored restoratives and bonding technology have made cosmetic dental procedures more palatable and feasible

In addition newer technology allows the general practitioner to handle many previously complex esthetic problems more simply conservatively and economically

Introduction

The fundamental objective of all restorations since centuries has been to create adhesion between two dissimilar surfaces mineralized tooth structure and the restorative materials

The invention of dentin bonding agent is like a - dream come true for dentistry which led to the beginning of new era of adhesive dentistry

The concept of dentistry with the introduction of adhesives has changed from - Extension for Prevention to PREVENTION OF EXTENSION

Introduction

The principles of adhesive dentistry dates back to 1955 when buonocore after observing industrial use of phosphoric acid to improve adhesion of paints and resin coatings to metal surfaces applied acid to the teeth to lsquorender the tooth surface more receptive to adhesionrsquo

Michael Buonocore

The traditional ldquodrill and fillrdquo approach is fading now because of numerous advancements taking place in restorative dentistry

ADHESIVE DENTISTRY

Adhesion The state in which two surfaces are held together by interfacial forces

which may consists of valence forces or interlocking forces or both (The American Society for Testing and Materials specification D 907)

Adherend The surface or substrate that is adhered

Adhesiveadherent A material that can join substances together resist separation and transmit loads across the bond

Adhesive failure The bond that fails at the interface between the two substrates

Cohesive failure The bond fails within one of the substrates but not at the interface

PRINCIPLES OF ADHESION

Adherend 1 Adherend 2

Adhesive Systemor Luting Cement

Interface 2Interface 1

DENTALJOINT

ENAMEL DENTIN gtLiner Base Cement gt

Post and Core gtDental Amalgam gt

Implant gt

lt Composite Amalgamlt Cast Inlay Onlay or Crownlt All-Ceramic Inlay Onlay or Crownlt Veneers Maryland Bridgeslt Orthodontic Brackets

AdhesiveInterface 1 DENTALADHESION

>

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The fundamental objective of all restorations since centuries has been to create adhesion between two dissimilar surfaces mineralized tooth structure and the restorative materials

The invention of dentin bonding agent is like a - dream come true for dentistry which led to the beginning of new era of adhesive dentistry

The concept of dentistry with the introduction of adhesives has changed from - Extension for Prevention to PREVENTION OF EXTENSION

Introduction

The principles of adhesive dentistry dates back to 1955 when buonocore after observing industrial use of phosphoric acid to improve adhesion of paints and resin coatings to metal surfaces applied acid to the teeth to lsquorender the tooth surface more receptive to adhesionrsquo

Michael Buonocore

The traditional ldquodrill and fillrdquo approach is fading now because of numerous advancements taking place in restorative dentistry

ADHESIVE DENTISTRY

Adhesion The state in which two surfaces are held together by interfacial forces

which may consists of valence forces or interlocking forces or both (The American Society for Testing and Materials specification D 907)

Adherend The surface or substrate that is adhered

Adhesiveadherent A material that can join substances together resist separation and transmit loads across the bond

Adhesive failure The bond that fails at the interface between the two substrates

Cohesive failure The bond fails within one of the substrates but not at the interface

PRINCIPLES OF ADHESION

Adherend 1 Adherend 2

Adhesive Systemor Luting Cement

Interface 2Interface 1

DENTALJOINT

ENAMEL DENTIN gtLiner Base Cement gt

Post and Core gtDental Amalgam gt

Implant gt

lt Composite Amalgamlt Cast Inlay Onlay or Crownlt All-Ceramic Inlay Onlay or Crownlt Veneers Maryland Bridgeslt Orthodontic Brackets

AdhesiveInterface 1 DENTALADHESION

>

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The principles of adhesive dentistry dates back to 1955 when buonocore after observing industrial use of phosphoric acid to improve adhesion of paints and resin coatings to metal surfaces applied acid to the teeth to lsquorender the tooth surface more receptive to adhesionrsquo

Michael Buonocore

The traditional ldquodrill and fillrdquo approach is fading now because of numerous advancements taking place in restorative dentistry

ADHESIVE DENTISTRY

Adhesion The state in which two surfaces are held together by interfacial forces

which may consists of valence forces or interlocking forces or both (The American Society for Testing and Materials specification D 907)

Adherend The surface or substrate that is adhered

Adhesiveadherent A material that can join substances together resist separation and transmit loads across the bond

Adhesive failure The bond that fails at the interface between the two substrates

Cohesive failure The bond fails within one of the substrates but not at the interface

PRINCIPLES OF ADHESION

Adherend 1 Adherend 2

Adhesive Systemor Luting Cement

Interface 2Interface 1

DENTALJOINT

ENAMEL DENTIN gtLiner Base Cement gt

Post and Core gtDental Amalgam gt

Implant gt

lt Composite Amalgamlt Cast Inlay Onlay or Crownlt All-Ceramic Inlay Onlay or Crownlt Veneers Maryland Bridgeslt Orthodontic Brackets

AdhesiveInterface 1 DENTALADHESION

>

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The traditional ldquodrill and fillrdquo approach is fading now because of numerous advancements taking place in restorative dentistry

ADHESIVE DENTISTRY

Adhesion The state in which two surfaces are held together by interfacial forces

which may consists of valence forces or interlocking forces or both (The American Society for Testing and Materials specification D 907)

Adherend The surface or substrate that is adhered

Adhesiveadherent A material that can join substances together resist separation and transmit loads across the bond

Adhesive failure The bond that fails at the interface between the two substrates

Cohesive failure The bond fails within one of the substrates but not at the interface

PRINCIPLES OF ADHESION

Adherend 1 Adherend 2

Adhesive Systemor Luting Cement

Interface 2Interface 1

DENTALJOINT

ENAMEL DENTIN gtLiner Base Cement gt

Post and Core gtDental Amalgam gt

Implant gt

lt Composite Amalgamlt Cast Inlay Onlay or Crownlt All-Ceramic Inlay Onlay or Crownlt Veneers Maryland Bridgeslt Orthodontic Brackets

AdhesiveInterface 1 DENTALADHESION

>

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

ADHESIVE DENTISTRY

Adhesion The state in which two surfaces are held together by interfacial forces

which may consists of valence forces or interlocking forces or both (The American Society for Testing and Materials specification D 907)

Adherend The surface or substrate that is adhered

Adhesiveadherent A material that can join substances together resist separation and transmit loads across the bond

Adhesive failure The bond that fails at the interface between the two substrates

Cohesive failure The bond fails within one of the substrates but not at the interface

PRINCIPLES OF ADHESION

Adherend 1 Adherend 2

Adhesive Systemor Luting Cement

Interface 2Interface 1

DENTALJOINT

ENAMEL DENTIN gtLiner Base Cement gt

Post and Core gtDental Amalgam gt

Implant gt

lt Composite Amalgamlt Cast Inlay Onlay or Crownlt All-Ceramic Inlay Onlay or Crownlt Veneers Maryland Bridgeslt Orthodontic Brackets

AdhesiveInterface 1 DENTALADHESION

>

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Adhesion The state in which two surfaces are held together by interfacial forces

which may consists of valence forces or interlocking forces or both (The American Society for Testing and Materials specification D 907)

Adherend The surface or substrate that is adhered

Adhesiveadherent A material that can join substances together resist separation and transmit loads across the bond

Adhesive failure The bond that fails at the interface between the two substrates

Cohesive failure The bond fails within one of the substrates but not at the interface

PRINCIPLES OF ADHESION

Adherend 1 Adherend 2

Adhesive Systemor Luting Cement

Interface 2Interface 1

DENTALJOINT

ENAMEL DENTIN gtLiner Base Cement gt

Post and Core gtDental Amalgam gt

Implant gt

lt Composite Amalgamlt Cast Inlay Onlay or Crownlt All-Ceramic Inlay Onlay or Crownlt Veneers Maryland Bridgeslt Orthodontic Brackets

AdhesiveInterface 1 DENTALADHESION

>

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Adherend 1 Adherend 2

Adhesive Systemor Luting Cement

Interface 2Interface 1

DENTALJOINT

ENAMEL DENTIN gtLiner Base Cement gt

Post and Core gtDental Amalgam gt

Implant gt

lt Composite Amalgamlt Cast Inlay Onlay or Crownlt All-Ceramic Inlay Onlay or Crownlt Veneers Maryland Bridgeslt Orthodontic Brackets

AdhesiveInterface 1 DENTALADHESION

>

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Diagrammatic representation of dental adhesive system where Adherend 1 is

enamel dentin or both Adhesive is bonding agent

Adherend 2 is composite resin

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

ADHESIVE DENTISTRY

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Indications of Bonding Techniques

Adhesive restorative techniques are currently used to accomplish the following

1 Restore Class I II III IV V and VI carious or traumatic defects 2 Change the shape and the color of anterior teeth 3 Improve retention for metallic crowns or for porcelain-fused-to-

metal crowns 4 Bond all-ceramic restorations 5 Bond indirect resin-based restorations 6 Seal pits and fissures 7 Bond orthodontic brackets 8 Bond periodontal splints and conservative tooth replacement

prostheses

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

9 Repair existing restorations (composite amalgam ceramic or ceramometal)

10 Provide foundations for crowns 11 Desensitize exposed root surfaces 12 Seal beneath or bond amalgam restorations to tooth structure 13 Impregnate dentin that has been exposed to the oral fluids making it

less susceptible to caries 14 Bond fractured fragments of anterior teeth 15 Bond prefabricated and cast posts 16 Reinforce fragile roots internally 17 Seal apical restorations placed during endodontic surgery

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Four different mechanisms of adhesion has been described

Mechanical adhesion ndash interlocking of the adhesive with irregularities in the surface of the substrate or adherend

Adsorption adhesion ndash chemical bonding between the adhesive and the adherend The forces involved may be primary (ionic or covalent) or secondary (hydrogen bonds dipole interaction or van der Waals) valence forces

Diffusion adhesion ndash interlocking between the mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across an interface

Electrostatic adhesion ndash an electric double layer at the interface of a metal with a polymer that is part of the total bonding mechanism

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Wetting is the ability of the liquid to flow easily over the entire surface and adhere to the solid

If the adhesive does not wet the surface of the adherend adhesion between the adhesive and adherend will be negligible or nonexistent

Wetting is principally influenced by

ndash Cleanliness of the adherend Cleaner surface greater adhesion ndash Surface energy of the adherend More surface energy greater

adhesion

FACTORS AFFECTING ADHESION

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The extent to which an adhesive wets the surface of the adherend may be determined by measuring the contact angle which is the angle formed by the adhesive with the adherend at their interface

The stronger the attraction of the adhesive for the adherend the smaller will be the contact angle

The zero contact angle is the best to obtain wetting

Contact angle

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Surface Energy

The surface tension of the liquid and the surface energy of the adherend ultimately determine the degree of wetting that occurs

Generally the harder the surface the higher the surface energy will be which means that adhesive properties of the material will be higher

Factors Affecting Adhesion

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Surface Contamination

The substrate surface should be clean as contamination prevents the adhesion

Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact

Factors Affecting Adhesion

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Water

The higher the water content the poorer is the adhesion

Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion

Factors Affecting Adhesion

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Steps in Forming Good Adhesion

(1) Clean adherend

(2) Good wetting

(3) Intimate adaptation

(4) Bonding

(5) Good curing

physicalbonding

chemicalbonding

mechanicalbonding

+ndash

>

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

ENAMEL BONDINGbull To bond to enamel it is very important to focus on the mineral

component (hydroxyapatite) of enamel

bull Buonocore 1955 ndash was the first to reveal the adhesion of acrylic resin to acid

etched enamel ndash used 85 percent phosphoric acid for etching

bull Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion to the enamel

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

ENAMEL BONDING

If the concentration is greater than 50 percent Monocalcium phosphate monohydrate may get

precipitated

Concentrations lower than 30 percent Dicalcium phosphate monohydrate is precipitated which

interferes with adhesion

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

ENAMEL BONDING Percentage of etchants used

35 to 40

Use of lower concentrations of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentin

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Acid application time ideally 10 seconds

studies show that enamel should not be etched for more than 15 to 20 seconds

Scanning electron micrograph of enamel etched with 35 phosphoric acid (3M ESPE St Paul Minn) for 15 seconds

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Enamel acid etching ndash removes 10 micron of enamel

Creates microporous layer 5 to50 microns deep

Smooth surface ndash irregular surface with high surface energy 72dynescm

Unfilled liquid acrylic resin (enamel bonding agent)

Wets the surface

Enters into microporosities by capillary action

Two types of resin tags are formed

Macrotags microtags (form between enamel prisms peripheries ) (form at the core of

enamel prisms )

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Removes residual pellicle exposure to the inorganic crystallite component of enamel

Creates a porous layer with the depth of the pores ranging from 5-10 microm

Increases as the wettublity and surface area of the enamel substrate

Raises the surface energy of enamel with creation of reactive polar sites

EFFECTS OF ETCHING ON ENAMEL

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Silverstone et al (1975) studied the morphological changes in SEM produced on the acid etched enamel surface

Exposure of human enamel to conditioning solutions produces 3 basic etching patterns

PATTERN OF ETCHING

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Type I (Preferential prism center etching) Dissolution of prism cores without dissolution

of prism peripheries resulting in a honey comb appearance The average diameter of the hollowed prism core is measured as about 3microm This is the most commonest type of etching pattern

Type II Dissolution of peripheral enamel without dissolution of prism cores resulting in a cobblestone appearance

Type III Mixed pattern Etching pattern is less distinct and includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears unrelated to prism morphologyThis type of etching in general is associated with the presence of prism less enamel and appears as a generalized surface roughening

ETCHING PATTERNS

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Clinically a uniform dull appearance is an indication that the tooth surface has been adequately etched

Silverstone in 1974 showed that etched enamel surface under polarized light resulted in 3 zones

1 Etched Zone2 Qualitative Zone3 Quantitative Zone

MICROSCOPIC APPEARANCE OF ETCHED ENAMEL

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

1 Etched ZoneThis is the narrow zone of enamel at about 10microm in depth that is removed by etching The fully reacted mineral crystals are removed resulting in the exposure of more reactive surface This increased surface area and a reduced surface tension allows resin to wet in the etched surface more readily

2 Qualitative ZoneThis zone is about 20microm in depth and it is rendered porous during acid etching of the enamel when identified qualitatively using polarized light

3 Quantitative ZoneThis third zone is almost up to 20microm depth It is qualitatively indistinguishable from adjacent enamel and can be detected with quantitative polarized light In human enamel the pores may be spherical elongated or sometimes as large chamber that are connected to smaller channels called ink bottle systems

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The effect of acid etching on enamel depends on

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Steps for Enamel Bonding Clean and wash the teeth with

water

Isolate to prevent any contamination from saliva or gingival crevicular fluid

Apply acid etchant in the form of liquid or gel for10 to 15 seconds

Deciduous teeth require longer time for etching than permanent teeth because of the presence of aprismatic enamel in deciduous teeth

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Steps for Enamel Bonding

bull Now apply bonding agent and low viscosity monomers over the etched enamel surface

bull Generally enamel bonding agents contain Bis-GMA or UDMA with TEGDMA added to lower the viscosity of the bonding agent

bull The bonding agents due to their low viscosity rapidly wet and penetrate the clean dried conditioned enamel into the microspaces forming resin tags

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Fluorosed teeth have an altered structure composition and appearance

With the increase in severity of fluorosis enamel becomes more porous and sub-surface lesion extends towards the inner enamel

Several studies have shown that composites can be bonded successfully to fluorosed enamel depending on the degree of fluorosis

It is always recommended to grind the enamel before bonding as it is seen that bond strength of composites to ground enamel of teeth with moderate fluorosis is similar to that of normal teeth

Acid etching is good for enamel bonding but not for dentin bonding in fluorosed teeth As a consequence a good choice of adhesive it would be a two-step self etch adhesive with an additional acid etching step for the enamel

Bonding to fluorosed teeth

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Dentin Bonding

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Dentin Bonding Adhesion of restorative materials to enamel has become a

routine and reliable aspect of modern restorative dentistry

But adhesion to dentin has proved to be more difficult and less predictable

Much of the difficulty in bonding to dentin is the result of the complex microstructure and variable composition of dentin in different areas of the tooth

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Thus the composition of dentin is much different than that of enamel and one would expect it to behave differently when etched with acid

The presence of water and organic components lower the surface energy of dentin and make bonding with hydrophobic resins essentially impossible

Enamel vs Dentin

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ)

A cuff of hypermineralized dentin called peritubular dentin lines the tubules

The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding

The intertubular dentin is penetrated by submicron channels which allow the passage of tubular liquid and fibers between neighboring tubules forming intertubular anastomoses

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Dentin is an intrinsically hydrated tissue penetrated by a maze of 1- to 025-μm-diameter fluid-filled dentin tubules

Movement of fluid from the pulp to the DEJ is a result of a slight but constant pulpal pressure

Pulpal pressure has a magnitude of 25 to 30 mm Hg or 34 to 40 cm H2O

Dentinal tubules enclose cellular extensions from the odontoblasts and are in direct communication with the pulp

Inside the tubule lumen other fibrous organic structures are present such as the lamina limitans which substantially decreases the functional radius of the tubule

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Relative number of dentin tubules and tubule volume at different dentin levels as measured at different distances from the dentinoenamel Junction Adapted from Heymann 1995

Distribution of tubules in dentinDentin close to the pulp shows a

higher tubule density than indentin remote from the pulpThe higher the tubule densitythe lower the bond strength

values of the dentin adhesives tothe dentin

The relative area occupied by dentin tubules decreases with increasing distance from the pulp

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Created whenever dentin is cut or ground with hand or rotary dental instruments and is about 1 to 5 μm thick (Brannstrom 1982)

It consists of debris that presumably reflects the composition of the underlying dentin

Thus the composition of superficial versus deep smear layers would be expected to be quite different

It has a uniform amorphous structure which appears to completely occlude the orifices of all dentinal tubules

Smear plugs are projections of the smear layer that extend to variable distances into dentinal tubules when the smear layer is created

Smear layer

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The smear layer has both advantages and disadvantages in the bonding process (Yap et al 1994)

Advantages include

Reduction of dentin permeability to toxins and oral fluids Reduction of diffusion (usually inwards) and convection of fluids

(outwards by hydrostatic pressure or inwards for example while restorations are cemented)

Reduction of wetness of cut dentin surfaces and Prevention of bacterial penetration of dentinal tubules

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Wetness and the harboring of bacteria or their products

It reduces the surface energy which compromises surface wetting

Prevents the intimate surface contact between the adhesive and dentin substrate and

Prevents resin penetration into dentinal tubules (Gwinnett 1984 Rees and Jacobsen 1990)

It acts like a separating agent since it is an intrinsically weak structure (5 to 6 MPa cohesive strength) that bond weakly to the underlying dentin (Tao and Pashley 1988)

Further the mineral component of the smear layer may dissolve slowly under a leaking restoration or may be removed by acid produced by bacteria to leave a gap which in turn increases marginal leakage and possibly secondary caries

Disadvantages include

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Factors such as

radius and length of the tubules the viscosity of dentin fluid the pressure gradient the molecular size of the substances dissolved in the

tubular fluid and the rate of removal of substances by the blood vessels in

the pulp affect permeability

All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding

Several additional factors affect dentin permeability

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The factors important in understanding the over all lsquobonding equationrsquo is

Dentin factors Tooth factors Patient factors Material factors Clinical factors

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Quality of dentin Higher bond strength is achieved for younger teeth

compared to the dentin of elderly patients

Altered dentin (sclertic or carious)

Variation in density of the tubules

Location of dentin (whether peripheral or close to pulp)

Etching of dentin (too long etching results in impeded hybrid layer formation and produces a weaker bond strength

The dentin should not be desiccated it must be kept moist during the entire procedure If it dries up the collagen structure collapses

Dentin factors

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Tooth factors The tooth factors include

Lesion size and shapeEnamel and dentin structureTooth flexureTooth locationFluoride content Surface roughness

Patient factorsPatient factors associated with dentin adhesion arebullThe degree of occlusal stressbullPatientrsquos age

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Saliva andor blood contamination Moisture contamination from handpieces or air-water

syringes Oil contamination from handpieces or air-water syringes Surface roughness of tooth surface Mechanical undercuts in tooth preparation Fluoride content of teeth Presence of plaque calculus extrinsic stains or debris Presence of bases and liners on the prepared teeth

Clinical factors

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Conditioner (Cleanser Etchant)

Conditioner is usually a weak organic acid (eg maleic acid) a low concentration of a stronger inorganic acid (eg phosphoric or nitric acid) or a chelating agent (eg EDTA)

Main Actions Heavily alters or removes the smear layer Demineralizes peritubular and intertubular surface dentin and

thereby exposes collagen fibrils Demineralizes up to a depth of 75 microns Depth of demineralization depends on type of acid its

concentration and etching time More mineralized peritubular dentin is etched more deeply

than the intertubular dentin Increases dentin permeability by 4 to 9 times

DENTIN BONDING SYSTEM

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Primer is usually a bifunctional monomer in a volatile solvent such as acetone or alcohol a bifunctional monomer is one that has a hydrophilic end (ie one with an affinity for water) and a hydrophobic end (one lacking an affinity for water)

Examples of bifunctional monomers include HEMA (hydroxyethyl methacrylate) NMSA (N-methacryloyl-5- aminosalicylic acid) NPG (N-phenylglycine) PMDM (pyromellitic diethylmethacrylate) and 4-META (4- methacryloxyethyl trimellitate anhydride)

Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Monomer Hydrophilic Monomer)

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Links the hydrophilic dentin to the hydrophobic adhesive resin is able to do this because of its bifunctional nature (ie primers hydrophilic end bonds to the wet dentin and its hydrophobic end bonds to the adhesive resin)

Promotes infiltration of demineralized peritubular and intertubular dentin by its own monomers and those of the adhesive resin

Increases wettability of the conditioned dentin surface and increases contact between the dentin and resin

Main Actions

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Adhesive is an unfilled or partially filled resin may

contain some component of the primer (eg HEMA) in an attempt to promote increased bond strength

Main Actions

Combines with the primerrsquos monomers to form a resin-reinforced hybrid layer (resin-dentin interdiffusion zone) from 1 to 5 microns thick

Forms resin tags to seal the dentin tubules provides methacrylate groups to bond with the subsequently placed resin composite

Adhesive (Bonding Resin Sealing Resin)

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

One of the first products that used this method for enamel and dentin treatment was Scotchbond Multi-Purpose Adhesive which used 10 to 12 maleic acid

Scotchbond MPA and most other current-generation products now use the same acid for etching dentin that they use for etching enamel (ie concentrations of phosphoric acid that range from 32 to 40)

This method of etching dentin with a 32 to 40 concentration of phosphoric acid is called the total-etch technique and was first discussed by Fusayama in 1977

Combining Enamel and Dentin Conditioners

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Acid washing rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules Rehydration priming

Swells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Mechanism of Bonding Ideally a dentin bonding agent should have both

hydrophilic and hydrophobic ends The hydrophilic end displaces the dentinal fluid to wet the surface The hydrophobic end bonds to the composite resin

bull Mechanism of BondingM R X

bull Where M is the double bond of methacrylate which copolymerizes with composite resin

bull R is the spacer which makes the molecule largebull X is a functional group for bonding which bonds to

inorganic or organic portion of dentin

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Mechanism of Bonding

Bonding to the inorganic part of dentin involves ionic interaction among the negatively charged group on X for example phosphates amino acids and amino

alcohols or dicarboxylates) and the positively charged calcium ions

Commonly used bonding systems employ use of phosphates

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Mechanism of Bonding

bull Bonding to the organic part of dentin ndash Interaction with

bull Amino (ndashNH) bull Hydroxyl (ndashOH) bull Carboxylate (ndashCOOH) bull Amide (ndashCONH) groups

bull Dentin bonding agents have ndash isocyanates ndash aldehydes ndash carboxylic acid ndash anhydrides and ndash carboxylic acid chlorides

which extract hydrogen from the above mentioned groups

and bond chemically

present in dentinal collagen

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

EVOLUTION OF DENTIN BONDING SYSTEM

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Developed in 1960s

Relied on adhesion to smear layer

No of steps involved were two etching of enamel + application of adhesive

Did not recommend dentin etch

Bowen formulated Cervident containing N-phenylglycine glycidyl methacrylate (NPG-GMA)

NPG-GMA is a surface-active comonomer that theoretically could mediate water- resistant chemical bonds of resin to dentinal calcium

First generation

Adhesive resin

Smear layer

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

This means that one end of this molecule bonds to dentin while the other polymerizes with composite resin

bond strengths - 2 to 3 MPa

The clinical results with these systems were poor

No improvement in marginal leakage when compared to conventional unfilled enamel bonding resins (Barkmeier and Cooley 1991)

Based on Carbon-13 NMR analysis it appears that no ionic bonding actually develops between NPG-GMA and hydroxyapatite (Jorge Perdigao Edward Swift)

First generation

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

In the late 1970s the second-generation systems were introduced

Incorporated halophosphorus esters of unfilled resins such as bisphenol-A glycidyl methacrylate (Bis-GMA) or hydroxyethyl methacrylate (HEMA) which substituted methacrylate

Mechanism by which they bond to dentin was postulated to be through an ionic bond to calcium by chlorophosphate groups

The clinical performance of these bonding agents was relatively poor

Shear dentinal bond strengths of only 2 to 6 MPa were reported

SECOND GENERATION

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

A major reason for the poor performance of these bonding agents is the fact that they bond to the smear layer rather than to the underlying dentin hence

Their bond strength is limited by the cohesive strength of the smear layer or the adhesion of the smear layer to the dentin below (Tao et al 1988)

These bond strengths were not great enough to counteract contraction stress generated by shrinking composites which is estimated to exceed 20 MPa in some cavities

Furthermore some studies indicate that bonds between phosphate esters and dentin may also be hydrolyzed by immersion in water

Therefore composite resin tends to separate from dentin forming gaps at restoration margins and increasing the microleakage at margins in dentin or cementum

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Etched tubule dentin bonding agents Representative brand Dentin Bonding System (Den-Mat) Phosphate ester dentin bonding agents

Representative brands Bondlite (SDSKerr) Creation Bond (Den-Mat) Prisma Universal Bond (Caulk) and Scotchbond (3M)

Polyurethane dentin bonding agents Representative brand Dentin-Adhesit (Ivoclar Vivadent)

There were three types of second-generation products

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

In third generation the smear layer was partially removed or modified rather than complete removal

In most of the systems the phosphate primer modifies the smear layer by softening it after penetration it cures forming a hard surface

The adhesive is then applied attaching the cured primer to the composite resin

Bonding to smear layer-covered dentin was not very successful before 1990 however because the resins did not penetrate through the smear layer bond was weak approached 10-12 MPa (Leinfelder 1993)

THIRD GENERATION

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The basis of third generation systems was laid in 1979 when the Japanese philosophy of acid-etching the dentin to remove the smear layer gained acceptance

The acid opens dentinal tubules partially and increases their permeability to form micromechanical attachment

Based on this total-etch concept Clearfil New bond was introduced in 1984 which contains HEMA and 10-methacryloyoxy-decyl-dihydrogen phosphate (10-MDP) which had long hydrophobic and short hydrophilic components as active components

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

3rd generation

1st step -Total etchingLeaving free minerals on surface-Rinse surface-Total drying of surface

2nd step adding primer

3rd stepAdding adhesive resinThen adding Composite

Smear layer Residual water Primer Adhesive

3rd generation

Composite

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Fourth generation bonding agents-etch and rinse adhesives-three step adhesives-total etch adhesives

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Fourth-generation dentin adhesives were introduced for use on acid etched dentin

Because the clinical technique involves simultaneous application of an acid to enamel and dentin this method is commonly known as the total-etch technique

Also called the etch and rinse technique it was the most common strategy for dentin bonding during the 1990s and remains popular today

Application of acid results in partial or total removal of smear layer and demineralization of underlying dentine up to depth of 75 microns

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Application of acid to dentin partial or total removal of the smear layer and demineralization of intertubular and peritubular dentin

open dentin tubules and exposed collagen fibers increased microporosity of the intertubular dentin

Dentin is demineralized by up to 75 μm depending on the type of acid application time and concentration

The primer in a three-step system is designed to increase the critical surface tension of dentin

When primer and bonding resins are applied to etched dentin they penetrate the intertubular dentin forming a resin-dentin interdiffusion zone or hybrid layer

They also penetrate and polymerize in the open dentinal tubules forming resin tags

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

In the three-bottle total etch bonding technique acid is used to remove the smear layer and smear plugs from the dentin and to remove peritubular dentin increasing the

diameter of the tubules thereby (Fig A) that will form stronger resin tags The etched surface is then primed with dilute methacrylates (red) in a volatile solvent (Fig B) to insure that the matrix is expanded and precoated with methacrylates Then a solvent-

free adhesive (green) is applied that diffuses into the primed surface and down into the tubules where it polymerizes with the primer (Fig C)

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Fourth-generation adhesives such as All-Bond 2 OptiBond FL and Scotchbond Multipurpose are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol acetone andor water

An unfilled or filled fluid boding agent-hydrophobic monomer such as Bis-GMA combined with hydrophilic HEMA

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

All-Bond 2 and Scotchbond Multipurpose are two of the first fourth-generation adhesive systems which rely on the hydration of dentin as a critical parameter for effective bonding

All-Bond 2 uses a phosphoric acid enameldentin conditioning step to be followed by the application of hydrophilic primers containing N-tolyglycine-glycidyl methacrylate (NTG-GMA) and biphenyl methacrylate (BPDM) in acetone

This priming layer is followed by an unfilled resin containing Bis-GMA and HEMA

The original Scotchbond Multipurpose conditioned dentin with 10 maleic acid solution followed by a primer consisting of an aqueous layer of HEMA and Vitrebond copolymer

The adhesive resin system is also a Bis-GMA resin containing HEMA Later maleic acid was replaced by phosphoric acid to generate more consistent results

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Other fourth-generation adhesive systems include

Imperiva Bond (acid treatment ndash primer containing HEMA amp 4-acryloxyethyltrimeric acid - Triethylene glycol dimethacrylate (TEGDMA) dimethylamino ethylmethacrylate and butylated hydroxytolune (BHT)

Permaquik (acid conditioning- ethanol based primer (naturally occurring elastic resin+ Canada balsam+HEMA)- adhesive resin (Bis-GMA+glass filler)

Optibond and Solidbond employs partially filled adhesive resins use of fillers in the adhesive resin exhibits less shrinkage in the bonding layer

It is hypothesized that generating less residual shrinkage stress in the adhesive reduces bond failures

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

ProBOND is unique in that it does not require dentin conditioning

It consists of an acetoneethanol primer with a phosphate adhesion promoter PENTA and an adhesive containing a urethane dimethacrylate resin (UDMA) PENTA and glutaraldehyde

Liner Bond 2 introduced the concept of a no-rinse self-etching primer

The primer consisted of pheny-P HEMA and N-methacryloyl 5-aminosalicyclic acid (5-NMSA) and

a bonding resin containing 10-methacryloyldecyl dihydrogen phosphate (MDP) Bis-GMA and colloidal silica

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

An additional feature of fourth-generation systems is the claim for their utility in multipurpose applications

In addition to dentin and enamel adhesion bond strength claims were made for cast alloys amalgam and porcelain

Mean shear bond strength of the fourth-generation systems are reported to range from 17MPa to great than 34MPa

If the clinician carefully adhered to the specific recommendations made regarding the methods and times required for application of the bonding agent the results were highly effective

Shear bond strengths to both enamel and dentin routinely approximated 25 MPa

Such a process has permitted forms of esthetic and functional treatment not previously conceived

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

4th generation

1st step -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step adding primer

3rd stepAdding adhesive resin amp then composite

4th generation

Composite

Smear layer Residual water Primer Adhesive resin

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The etch-and-rinse adhesives were categorized according to their respective solvent

Ethanol-based adhesivesEg OptiBond Solo (and later OptiBond Solo Plus)

Acetone-based adhesives All- bond 2 and One-Step (BISCO)

Water-based adhesives Scotchbond MP and ScotchBond 1

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

These also are called the ldquoone bottlerdquo systems because they combine the primer and bonding agent into a single solution

A separate etching step still is required

The first of these products was LD Caulkrsquos Prime amp Bond When originally introduced it was to be used only when placing direct composite resin restorations

Recently it underwent two changes and has been renamed Prime amp Bond 21

The changes were addition of fluoride and inclusion of an elastomeric monomer to reduce the DBAlsquos rigidity

Fifth generation

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Other fifth-generation products include OptiBond Solo (SDSKerr) Single Bond (3M ESPE) PQ1 (Ultradent) and Gluma One Bond (Heraeus Kulzer)

In general these products have limitations

Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multisubstrate bonding

It also appears important to apply multiple coats of these agents so that there is an adequately thick resin layer on top of the hybrid layer

This helps protect the DBA from early failure when the resin composite shrinks during polymerization

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Recently have been marketed

Contains extremely small filler particles

Include the products Prime amp Bond NT (DentsplyCaulk) and Excite (Ivoclar Vivadent)

Prime amp Bond NT contains 7 nanometer fillers has a greater concentration of resin and a smaller molecular weight resin

These changes are said to make the DBA tougher stronger and able to cover adequately with a single coat

it is also claimed to penetrate dentin better provide improved marginal integrity and have a low film thickness

Ivoclar Vivadentrsquos Excite contains 12-nanometer fillers and is packaged in a single-use capsule It is very fast to apply covers dentin in one coat and comes with a graphics-only instruction card

Nanofilled

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Sixth Generation Dentin Bonding Agents Introduced in the late 1990s and early 2000s

Self-etching primer and adhesive Available in two bottles

Primer Adhesive

Primer is applied prior to the adhesive Water is the solvent in these systemsSelf etching adhesive Available in two bottles

Primer Adhesive

A drop from each bottle is taken mixed and applied to the tooth surface for example Prompt L-pop

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Sixth Generation Dentin Bonding Agents

Mechanism of bonding In these agents as soon as the decalcification process starts infiltration of the empty spaces by the dentin bonding agent is initiated

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Advantages of Self Etching Primers

Comparable adhesion and bond strengths to enamel and dentin

Reduces postoperative sensitivity because they etch and prime simultaneously

They etch the dentin less aggressively than total etch products

The demineralized dentin is infiltrated by resin during the etching process

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Advantages of Self Etching Primers

Since they do not remove the smear layer the tubules remain sealed resulting in less sensitivity

They form a relatively thinner hybrid layer than traditional product which results in complete infiltration of the demineralized dentin by the resin monomers This results in increased bond strength

Much faster and simpler technique

Less technique sensitive as fewer number of steps are involved for the self etch system

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Xeno III

Clearfil se bond

prompt l pop

Examples

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Seventh Generation Bonding Agents

They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component single bottle one-step self-etch adhesive thus avoiding any mistakes in mixing

Developed in late 2000s All in one concept ie components available as single component Uses self etch primer Good bond strength No postoperative sensitivity Also have disinfecting and desensitizing properties They have attained consistently lower bond strengths than the

fourth and fifth-generation adhesives

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Laboratory studies show that bond strengths and margin sealing to be equal to the sixth-generation systems

iBondTM is a seventh-generation single-component no-mix one-step application dental adhesive with an etchant adhesive desensitizer and photoinitiator

Laboratory testing confirms that iBondTM has physical characteristics similar to other self-etching adhesives and may be used in all clinical situations where dental adhesives are required

Seventh-generation

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

GC has also introduced one component self-etching light-cured adhesive under trade name of G-BOND

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

STEP 4TH GEERATION 5TH GENERATION

6TH GENERATION

6TH GEN(MIXING REQUIRED)

7TH GEN

SELF ETCHING ADHESIVE

SELF ETCHING ADHESIVE

Etching of enamel dentine

Etchant Etchant Self etching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Priming of dentin

Primer Self-priming resinsealer

Self ndashetching primer

Self-etching self-priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Sealing of enamel and dentine

Resinsealer Self-priming resinsealer

Resinsealer Self etching self priming resinsealer

Self-etching self-priming resinsealer desensitizer disinfectant

Comparison of the Classification and Components of Dental Adhesive Systems

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

A new category of composite resin restorative materials which include what could be referred to as an ldquoeighth-generationrdquo bonding system has just become available for use

This new technology features a bonding agent which is contained within the composite resin restorative material

A self-etching self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures

Utilizing previous adhesive technology (found in the OptiBond system [Kerr]) this new self-etching self-bonding flowable composite resin system (Vertise Flow [Kerr]) simplifies the placement of direct composite restorations

Eighth-generation self-etching self-bonding

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Since fifth- sixth- and seventh-generation systems are incompatible with self-cure materials and dual-cure materials that cannot be effectively light-cured

Futura bond DC dual cured It is dual-cured and works with all light- self- or dual-cured

resins It takes only 35 sec from start to finish It needs only one coat Futurabond DC cures without any light in the self-cured

mode This is a big advantage for root canal cementation Futurabond DC eliminates the problem of the ldquopooling

effectrdquo with moisture

Eighth-generation

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

A new system would be developed that had the best attributes of the fourth generation and the ease of the sixth-generation bonding systems and that system is Surpassreg from Apex

Surpass is an eighth-generation material because it is very different from other generations

It consists of three bottles an etchantconditioner a primer and a separate hydrophobic bonding resin

In that regard it resembles fourth-generation materials but the etchantconditioner is not rinsed from the tooth

Thus Surpass also has characteristics of the sixth generationmdashthe ease of a no-rinse system but the performance of a fourth-generation system

Eighth-generation

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Surpass 1 is applied to the dentin and enamel for about 10 seconds agitating gently

Three brushfuls of Surpass 2 are then applied right onto the wet preparation

Once the three brushfuls have been applied the preparation is dried thoroughly for 10 seconds It cannot be overdried and the drier the tooth is following application of Surpass 2 the better the result

Then a layer of Surpass 3 is applied to the preparation and light-cured for 10 seconds

This is the only technique for Surpass no matter what kind of procedure is being performed

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Surpass may be used with any resin materialsmdashdual-cure self-cure and light-curemdashand no catalysts are required

For use with indirect restorations Surpass is simply made very thin prior to light-curing

For direct restorations the bonding resin can be made to the desired thickness although a thin uniform layer is recommended

Surpass dentin bond strengths have been demonstrated to be in the mid-50 MPa range

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

HYBRID LAYER AND HYBRIDIZATION

A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer

When a bonding agent is applied part of it penetrates into the collagen network known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration

In intertubular penetration it polymerises with primer monomers forming a hybrid layerresin reinforced layer

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Hybridization (Given by Nakabayachi in 1982)

Hybridization is the process of formation of a hybrid layer The hybrid layer is the phenomenon of formation of a resin

interlocking in the demineralized dentin surface The hybrid layer is responsible for micromechanical bonding between tooth and resin

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Hybridization (Given by Nakabayachi in 1982)

When dentin is treated with a conditioner it exposes the collagen fibril network with interfibrillar microporosities

These spaces are filled with low viscosity monomers when primer is applied

This layer formed by demineralization of dentin and infilteration of monomer and subsequent polymerization is called the hybrid layer

Hybridoid layer is that area of demineralized dentin into which resin fail to penetrate

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Zones of the Hybrid Layer

1 Top layer Consists of loosely arranged collagen fibrils and interfibrillar spaces filled with resin

2 Middle layer Consists of interfibrillar spaces in which hydroxyapatite crystals have been replaced by resin monomer because of the hybridization process

3 Bottom layer Consists of almost unaffected dentin with a partly demineralized zone of dentin

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

The hybrid layer promotes good bond strength

Behaves like an impermeable membrane that can prevent noxious stimuli from invading pulpal tissue through dentinal tubules

Hybridized dentin reduces the risk of microleakage incidence of secondary caries and post-operative sensitivity

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Diagrammatic presentation of different zones of hybrid layer

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

OVER-ETCHING

Concerns have been raised that aggressive etching of the dentin may cause demineralization to a depth that might be inaccessible to complete resin impregnation

If this occurred a collagenous band at the base of the hybrid not impregnated by resin would dramatically weaken the resin-dentin bond and consequently the durability of bond

Incomplete resin penetration has been described as causing a microporous dentinal zone at the base of hybrid layer (Sano et al 1994) which is thought to be a pathway for nanoleakage of fluids causing hydrolysis of collagen and a reduction in longevity of bond

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Moist vs Dry Dentinbull By etching dentin the smear layer and minerals from it are removed exposing

the collagen fibers

bull Areas from where minerals are removed are filled with water

bull This water acts as a plasticizer for collagen keeping it in an expanded soft state

bull Thus spaces for resin infiltration are also preserved But these collagen fibers collapse when dry and if the organic matrix is denatured

bull This obstructs the resin from reaching the dentin surface and forming a hybrid layer

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Moist vs Dry Dentinbull The desired effect of acid etching which is increased permeability

bull For this reason presence of moistwet dentin is needed to achieve successful dentin bonding

bull When primer is applied to wetmoist dentin water diffuses from the primer to the organic solvent and the solvent diffuses along with the polymers into the demineralized dentinal matrix and tubules

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Schematic (on the left) and transmission electron micrograph on the right of the ldquoover-wetrdquo phenomenon In the total-etch wet bonding technique there is the danger that some regions in complex cavity preparations (such as proximal boxes) may be too wet When single bottle primeradhesives are applied the solvent may diffuse into the water forcing adhesive monomers to undergo phase changes forming blisters resin globules etc Note that although the etched intertubular dentin has taken up resin to form hybrid layers (red zone on left) the adhesive (blue) did not form resin tags but left the tubules in communication with microblisters filled with water (light blue)

These blisters may compress when the restoration is under occlusal function forcing dentinal fluid toward the pulp and causing post-operative sensitivity This is one of the possible complications of this technique-sensitive

bonding method

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Transmission electron micrographs of dentin bonded with an all-in-one adhesive then placed in 37ordmC water for 24 hrs prior to soaking in silver nitrate to demonstrate the presence of water-filled (now silver-filled) channels called ldquowater treesrdquo (finger-pointers) extending from the hybrid layer (H) and passing through the cured adhesive layer The black silver deposits indicate where there

were water-filled channels Such water trees do not form in self-etching primer adhesives

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Modern dentin adhesives systems are classified as

Group one Modify the smear layer and incorporate in the bonding process They are further classified in one step and two step smear layer modifying system

Group two Complete removal of the smear layer Again they are

further classified in two and three step removing systems depending on a combined or a separate application of a primer and adhesive resin

Group three Dissolve the smear layer

Other classification systems

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Simple classification scheme for dentin bonding systems using a formula method first proposed by John Kanca (2004)

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

3-COMPONENT SYSTEMS (E + nP + B)

Scotchbond Multipurpose Plus (3M) Permaquick (Ultradent) Bond-It (Jeneric Pentron) All-Bond 2 (BISCO) Tenure ABS (Denmat) ProBond (Dentsply)

2-COMPONENT SYSTEMS (nEP + B)

Clearfil SE Bond amp LinerBond 2v (Kuraray) Tyrian SPE (Bisco) Optibond Solo SE Plus (Kerr) Fluoro Bond (Shofu) UniFil Bond (GC) Mac Bond II (Tokuyama) NanoBond (Pentron)

2-COMPONENT SYSTEMS (E + nPB)

Syntac Single Component (Ivoclar) Ecusit PrimerMono (DMG Hamburg) One Coat Bond (Coltene Whaledent) Bond-1 (Jeneric Pentron) Tenure Quik with Fluoride (Denmat) Solid Bond (Hereaus-Kulzer) Imperva Bond (Shofu) EG Bond (Sun Chemical) PQ1 (Ultradent) Easy Bond (Parkell) Paama 2 and Stae (SDI) PrimeampBond NT (Dentsply) Single-Bond (3M) Optibond Solo and Solo Plus (Kerr) One-Step (BISCO) Excite (IvoclarVivadent) OSB Bonding System (ESPE) IntegraBond (Premier)

1-COMPONENT SYSTEMS (nEPB) AQBond (Sun Medical) or Touch-and-Bond (Parkell) Adper Prompt or LP3 (3M-ESPE) Solist (One-bottle-bond) (DMG Hamburg) iBond (Hereaus-Kulzer) Xeno III (Dentsply)

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Modern adhesives can also be classified as (Van Meerbeek et al 2001 2003)

ETCH AND RINSE SELF ETCH ADHESIVES RESIN MODIFIED GLASS ADHESIVES IONOMER

Classification of bonding agents based on their shear bond strength (Eick et al1991)

Besides the use of dentin bonding agent as a normal part of resin bonding they have other clinical applications like

Metal-Resin bonding of indirect resin-bonded inlay onlay crown or veneer

As amalgam bonding agent Prevention and treatment of hypersensitivity In establishing apical and coronal seal of the root along with resin Pulp capping agent As a protective coat for glass ionomer restorations

OTHER USES OF DENTIN BONDING AGENT

Amalgam BondingA technique to bond amalgam to the cavity

Aims Behind lsquoBonded Amalgamsrsquo

Conserve more tooth structure by reducing the need to remove sound tooth tissue for mechanical retention

Increased Amalgam retention

Reduce marginal leakage

Reduce the need for dentine pins

Potentially reduce sensitivity

Improve fracture resistance

Improved amalgam margins

Materials for Amalgam Bonding Resin Cements ( Panavia)

Adhesive Bonding Agents-initially designed for composites-OptiBond solo-Amalgambond-Scotchbond multipurpose

OptiBond solo

How do they work

Etching dentine opens up dentinal tubules enabling adhesive resin to flow into dentine and is retained micromechanically

Adhesive resin adheres to amalgam roughness micromechanically and by 4-META adhesive

Claimed Advantages of Amalgam Bonding Techniques

Decreased microleakage YES

Increased amalgam retention YES if cavity lacks mechanical retention

Avoids risk of using pins YES 20 of pins perforate 80oC rise

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used Panavia weakens amalgam

at margins Technique may reduce incidence of ditching

Tooth reinforcement YES if large cavity NO if small cavity

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Besides the use of dentin bonding agent as a normal part of resin bonding they have other clinical applications like

Metal-Resin bonding of indirect resin-bonded inlay onlay crown or veneer

As amalgam bonding agent Prevention and treatment of hypersensitivity In establishing apical and coronal seal of the root along with resin Pulp capping agent As a protective coat for glass ionomer restorations

OTHER USES OF DENTIN BONDING AGENT

Amalgam BondingA technique to bond amalgam to the cavity

Aims Behind lsquoBonded Amalgamsrsquo

Conserve more tooth structure by reducing the need to remove sound tooth tissue for mechanical retention

Increased Amalgam retention

Reduce marginal leakage

Reduce the need for dentine pins

Potentially reduce sensitivity

Improve fracture resistance

Improved amalgam margins

Materials for Amalgam Bonding Resin Cements ( Panavia)

Adhesive Bonding Agents-initially designed for composites-OptiBond solo-Amalgambond-Scotchbond multipurpose

OptiBond solo

How do they work

Etching dentine opens up dentinal tubules enabling adhesive resin to flow into dentine and is retained micromechanically

Adhesive resin adheres to amalgam roughness micromechanically and by 4-META adhesive

Claimed Advantages of Amalgam Bonding Techniques

Decreased microleakage YES

Increased amalgam retention YES if cavity lacks mechanical retention

Avoids risk of using pins YES 20 of pins perforate 80oC rise

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used Panavia weakens amalgam

at margins Technique may reduce incidence of ditching

Tooth reinforcement YES if large cavity NO if small cavity

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Amalgam BondingA technique to bond amalgam to the cavity

Aims Behind lsquoBonded Amalgamsrsquo

Conserve more tooth structure by reducing the need to remove sound tooth tissue for mechanical retention

Increased Amalgam retention

Reduce marginal leakage

Reduce the need for dentine pins

Potentially reduce sensitivity

Improve fracture resistance

Improved amalgam margins

Materials for Amalgam Bonding Resin Cements ( Panavia)

Adhesive Bonding Agents-initially designed for composites-OptiBond solo-Amalgambond-Scotchbond multipurpose

OptiBond solo

How do they work

Etching dentine opens up dentinal tubules enabling adhesive resin to flow into dentine and is retained micromechanically

Adhesive resin adheres to amalgam roughness micromechanically and by 4-META adhesive

Claimed Advantages of Amalgam Bonding Techniques

Decreased microleakage YES

Increased amalgam retention YES if cavity lacks mechanical retention

Avoids risk of using pins YES 20 of pins perforate 80oC rise

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used Panavia weakens amalgam

at margins Technique may reduce incidence of ditching

Tooth reinforcement YES if large cavity NO if small cavity

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Aims Behind lsquoBonded Amalgamsrsquo

Conserve more tooth structure by reducing the need to remove sound tooth tissue for mechanical retention

Increased Amalgam retention

Reduce marginal leakage

Reduce the need for dentine pins

Potentially reduce sensitivity

Improve fracture resistance

Improved amalgam margins

Materials for Amalgam Bonding Resin Cements ( Panavia)

Adhesive Bonding Agents-initially designed for composites-OptiBond solo-Amalgambond-Scotchbond multipurpose

OptiBond solo

How do they work

Etching dentine opens up dentinal tubules enabling adhesive resin to flow into dentine and is retained micromechanically

Adhesive resin adheres to amalgam roughness micromechanically and by 4-META adhesive

Claimed Advantages of Amalgam Bonding Techniques

Decreased microleakage YES

Increased amalgam retention YES if cavity lacks mechanical retention

Avoids risk of using pins YES 20 of pins perforate 80oC rise

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used Panavia weakens amalgam

at margins Technique may reduce incidence of ditching

Tooth reinforcement YES if large cavity NO if small cavity

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Materials for Amalgam Bonding Resin Cements ( Panavia)

Adhesive Bonding Agents-initially designed for composites-OptiBond solo-Amalgambond-Scotchbond multipurpose

OptiBond solo

How do they work

Etching dentine opens up dentinal tubules enabling adhesive resin to flow into dentine and is retained micromechanically

Adhesive resin adheres to amalgam roughness micromechanically and by 4-META adhesive

Claimed Advantages of Amalgam Bonding Techniques

Decreased microleakage YES

Increased amalgam retention YES if cavity lacks mechanical retention

Avoids risk of using pins YES 20 of pins perforate 80oC rise

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used Panavia weakens amalgam

at margins Technique may reduce incidence of ditching

Tooth reinforcement YES if large cavity NO if small cavity

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

OptiBond solo

How do they work

Etching dentine opens up dentinal tubules enabling adhesive resin to flow into dentine and is retained micromechanically

Adhesive resin adheres to amalgam roughness micromechanically and by 4-META adhesive

Claimed Advantages of Amalgam Bonding Techniques

Decreased microleakage YES

Increased amalgam retention YES if cavity lacks mechanical retention

Avoids risk of using pins YES 20 of pins perforate 80oC rise

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used Panavia weakens amalgam

at margins Technique may reduce incidence of ditching

Tooth reinforcement YES if large cavity NO if small cavity

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

How do they work

Etching dentine opens up dentinal tubules enabling adhesive resin to flow into dentine and is retained micromechanically

Adhesive resin adheres to amalgam roughness micromechanically and by 4-META adhesive

Claimed Advantages of Amalgam Bonding Techniques

Decreased microleakage YES

Increased amalgam retention YES if cavity lacks mechanical retention

Avoids risk of using pins YES 20 of pins perforate 80oC rise

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used Panavia weakens amalgam

at margins Technique may reduce incidence of ditching

Tooth reinforcement YES if large cavity NO if small cavity

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Claimed Advantages of Amalgam Bonding Techniques

Decreased microleakage YES

Increased amalgam retention YES if cavity lacks mechanical retention

Avoids risk of using pins YES 20 of pins perforate 80oC rise

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used Panavia weakens amalgam

at margins Technique may reduce incidence of ditching

Tooth reinforcement YES if large cavity NO if small cavity

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used Panavia weakens amalgam

at margins Technique may reduce incidence of ditching

Tooth reinforcement YES if large cavity NO if small cavity

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Clinical Indications Not recommended for routine amalgam cavities with

sufficient mechanical retention and undercuts No evidence of increased benefit to balance increased costs

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs

Some easier to use than others

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Bonding Agents Technique

Place matrix band ( lightly vaselined) Etch 10 phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Limitations of Technique Increased cost of restoration Technique sensitive Not in use long enough to permit adequate evaluation of

clinical performance Adhesion may breakdown over time

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Amalgam Bonding Summary

Amalgam is an excellent core build-up material for posterior teeth

Excellent interim restoration for posterior teeth

Adhesives can be used to improve retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

The choice may be ConfusingIt is easy for the clinician to believe that a new system is better over the old ones but this may not always be true

SOChemistry is more important than the companyTechnique is more important than the material

What we have to choose

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146

Thank you

• Slide 1
• Dentin bonding agents
• Contents
• Slide 5
• Introduction
• (2)
• Slide 8
• Slide 9
• PRINCIPLES OF ADHESION
• Slide 11
• Slide 12
• Slide 13
• Indications of Bonding Techniques
• (3)
• Slide 16
• FACTORS AFFECTING ADHESION
• Contact angle
• Slide 19
• Factors Affecting Adhesion
• Factors Affecting Adhesion (2)
• Factors Affecting Adhesion (3)
• Slide 23
• ENAMEL BONDING
• ENAMEL BONDING (2)
• ENAMEL BONDING (3)
• (4)
• Slide 28
• (5)
• (6)
• EFFECTS OF ETCHING ON ENAMEL
• PATTERN OF ETCHING
• ETCHING PATTERNS
• MICROSCOPIC APPEARANCE OF ETCHED ENAMEL
• Slide 35
• The effect of acid etching on enamel depends on
• Steps for Enamel Bonding
• Steps for Enamel Bonding (2)
• Bonding to fluorosed teeth
• Slide 40
• Dentin Bonding
• Dentin Bonding (2)
• Enamel vs Dentin
• (7)
• (8)
• Slide 46
• Slide 47
• Smear layer
• Slide 49
• (9)
• Disadvantages include
• Several additional factors affect dentin permeability
• (10)
• Dentin factors
• Slide 55
• Clinical factors
• DENTIN BONDING SYSTEM
• Primer (Adhesion Promoter Adhesion Enhancer Bifunctional Mono
• Main Actions
• Adhesive (Bonding Resin Sealing Resin)
• Combining Enamel and Dentin Conditioners
• Slide 62
• Slide 63
• Mechanism of Bonding
• Mechanism of Bonding
• Mechanism of Bonding (2)
• EVOLUTION OF DENTIN BONDING SYSTEM
• Slide 68
• First generation
• First generation (2)
• Slide 71
• SECOND GENERATION
• (11)
• There were three types of second-generation products
• THIRD GENERATION
• (12)
• Slide 77
• Fourth generation bonding agents -etch and rinse adhesives -thr
• (13)
• (14)
• Slide 81
• Slide 82
• (15)
• (16)
• (17)
• (18)
• Slide 87
• Slide 88
• Slide 89
• The etch-and-rinse adhesives were categorized according to thei
• Fifth generation
• Slide 92
• (19)
• Nanofilled
• Sixth Generation Dentin Bonding Agents
• Sixth Generation Dentin Bonding Agents (2)
• Slide 97
• Advantages of Self Etching Primers
• Advantages of Self Etching Primers (2)
• Slide 100
• Slide 101
• Seventh Generation Bonding Agents
• Seventh-generation
• Comparison of the Classification and Components of Dental Adhes
• Eighth-generation self-etching self-bonding
• Eighth-generation
• Eighth-generation (2)
• (20)
• Slide 110
• Slide 111
• HYBRID LAYER AND HYBRIDIZATION
• Hybridization (Given by Nakabayachi in 1982)
• Hybridization (Given by Nakabayachi in 1982) (2)
• Zones of the Hybrid Layer
• Slide 116
• Slide 117
• OVER-ETCHING
• Moist vs Dry Dentin
• Slide 120
• Moist vs Dry Dentin
• Slide 122
• Slide 123
• Slide 124
• Slide 125
• Other classification systems
• Simple classification scheme for dentin bonding systems using a
• Slide 128
• Modern adhesives can also be classified as (Van Meerbeek et al
• Classification of bonding agents based on their shear bond stre
• OTHER USES OF DENTIN BONDING AGENT
• Slide 132
• Aims Behind lsquoBonded Amalgamsrsquo
• Materials for Amalgam Bonding
• OptiBond solo
• How do they work
• Claimed Advantages of Amalgam Bonding Techniques
• Claimed Advantages of Amalgam Bonding Techniques (2)
• Clinical Indications
• Bonding Agents
• Limitations of Technique
• Slide 142
• Slide 143
• Amalgam Bonding
• Slide 145
• Slide 146