bonding materials

MATERIALS USED FOR DIRECT BONDING AND ENAMEL

PREPARATION

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CONTENTS• INTRODUCTION• HISTORY• TERMINOLOGY• STRUCTURE OF ENAMEL• DIRECT BONDING MATERIAL• COMPOSITES• GLASS IONOMERS• BONDING PROCEDURES• ENAMEL PREPARATIONS• ACID ETCHING• CRYSTAL GROWTH• AIR MICROABRASION• LASER ETCH• SAND BLASTING• REVIEW OF LITERATURE• CONCLUSION.


INTRODUCTION

• Introduction of the acid-etch bonding technique has led to dramatic changes in the practice of orthodontics.

• Buonocore ‘ 1955: demonstrated increased adhesion by acid pretreatment using 85% H3 PO4.

• Newman : began to apply these findings to direct bonding of orthodontic attachments.


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INTRODUCTION

• Retief ‘ 1975 : also described an epoxy resin system designed to with stand orthodontic forces

• Smith’1968: introduced Zinc polyacrylate (Carboxylate) cement, and bracket bonding and this cement was reported by Migrahi and Smith in ‘ 1969 .


– Miura etal ‘ 71 : described an acrylic resin (orthomite) using a modified trialkyl borane catalyst, that proved to be particularly successful for bonding plastic brackets and for enhanced adhesion in the presence of moisture

– also diacrylate resins , as both sealant ( eg. Nuvaseal) and adhesives were introduced into orthodontics.


– The most widely used resin, commonly referred to as “Bowens resin” or bis GMA(bispenol a glycicly dimethacrylate), was designed to improve bond strength and dimethacrylate was designed to improve bond strength and increased dimensional stability by cross linking.


HISTORY OF ADHESIVE BONDING SYSTEMS

• In 1955 Michael Buonocore was the first to describe the acid etch technique for enamel bonding. He reported that the adhesion of acrylic resins to enamel could be improved by conditioning the enamel with a solution of 85% phosphoric acid.


– In 1956 R.L. Bowen did the initial work on bis-GMA resin systems (Known as Bowen’s formula).

– In 1969 Masuhara introduced an orthodontic adhesive called direct bonding system for enamel. It was one of the first dental adhesive commercially introduced after Buonocore proposed the concept of acid-etching enamel.


– In 1975, Silverstone demonstrated the variation in the pattern of acid etching of human dental enamel examined by scanning electron microscopy. The demonstrated three patterns.

– In 1979 Maijer R. and Smith D.C. introduced an alternative to acid etching. They described a new method of bonding that involves crystal growth on the enamel surface.


DEVELOPMENT OF AN ADHESIVE BONDING SYSTEM

– Rafael L.Bowen and W.A. marjenhoff have reviewed the development of an adhesion system for bonding dental composites to dentin and enamel.


• Dr. Michael Buonocore is one of the best know pioneers in adhesive bonding of resins to teeth. He found that lightly etching enamel created a microporous surface into which direct filling liquid resin could flow. Polymerise and create a micromechanical attachment (1955).


– Dr. George Newman, one of Dr. Buonocore’s contemporaries developed similar methods to bond orthodontic brackets directly to the enamel of teeth (Newman. Snyder and Wilson, 1968).


– Composites have some troublesome properties even with a maximum proportion of inorganic filler particles.

- They exhibit some polymerization shrinkage.- A stiffness lower than that of the tooth.

• A coefficient of thermal expansion higher than that of the tooth crown


– Most situations involving dental adhesion really involves adhesive joints. The adhesive joint is the result of interactions of a layer of intermediate material, i.e., the adhesive, with two surfaces (adherends), producing two adhesive interfaces.


Terminology

• Adhesion :

is attraction between atoms and molecules at the surfaces of different materials when these surfaces are brought into contact. Forces of adhesion vary in magnitude and are physical or chemical.


• Physical Forces of Adhesion:

are that, account for most adhesive behavior are essentially electrostatic, involving the attraction between positive and negative charges. They are commonly known as Van der Wall’s forces and are mediated through interaction between dipoles (Keesom forces), induced dipoles (Debye forces), and nonpolar dispersion forces related to the polarizability of molecules (London force).

•


• Chemical forces of Adhesion : are the strongest forces of molecular attraction and are represented largely by ionic and covalent bonds between atoms. Chemical bonds produced is strong attachment and are usually more resistant to disruption by water than physical bonds.


• Cohesion : Cohesion is the molecular attraction due to the same physical forces involved in adhesion, except that these forces exist between like molecules instead of different molecules and are responsible for holding a material together


• Adhesive : In the broadest sense, an adhesive is a material that unites, joins, or attaches to itself or other substances by adhesion.


• Adherend: The adherend is the surface to which an adhesive is bonded generally to a solid surface


• Bonding agent : In dentistry, the bonding agent is a thin film of adhesive applied over a surface. A bonding agent is best used as a low viscosity material that easily and readily fills in the microscopic irregularities in a surface.

• It joins one substance to the other substance.


• Wetting : Wetting is a manifestation of the molecular attractive forces between materials. When the attractive forces are strong, an adhesive is more likely to fill in the microscopic irregularities in an adherend than if the forces were weak, other things beings equal.


• . Maximal wetting may be described as a state in which all of the interfacial contacts possible between adhesive and adherend surface have been established. A rough or porous surface can provide significantly increased bonding areas when properly wetted. The contact angle is considered an observable manifestation of wetting.


• .CONTACT ANGLE A zero contact angle indicates that the molecules of an adhesive are attracted or pulled toward the surface of the adherend with equal or greater force than they are attracted to themselves.


• Viscosity : Viscosity is a property of a fluid material, which essentially defines its consistency and can influence the contact angle, wetting and spreading phenomena.


• Mechanical Retention : Is considered a form of attachment not dependent on molecular attraction but rather predicated on the presence of structural retentive mechanisms. Structural retention may be of the gross variety, such as by undercuts, screws and bolts, or may involve more subtle mechanisms


• Bonding : Bonding is a general term that is used to describe the joining, uniting, or attaching of adhesives to an adherend. It is due to the physical or chemical forces of adhesion, and mechanical retention in undercuts, pores capillaries, and crevices.


NATURE OF ENAMEL

• It is the hardest tissue in the human body.• It is the only clinically visible mineralized

tissue.• It does not have the regenerative capacity

that bone and dentin possess.


• Enamel consists of microscopic units called enamel prisms.

• They represent as key hole shaped or fish like appearance

• They consist of a head and a tail portion


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• Each prism contains small units called hydroxyapetite crystals

• The crystals run parallel to the long axis of the prism in the head region and gradually become perpendicular as they approach the tail.


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• The crystals dissolves faster if they are oriented in a perpendicular relationship to the tooth surface that will be etched(head region of the prism)


DIRECT BONDING MATERIALS


Composites :

• A Composite material may be defined as a compound of two or more distinctly different materials with properties that are superior or intermediate to those at individual constituents.


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Chemistry of synthetic resins :

Synthetic resins are often called plastics.

Therefore It is these synthetic resins which impart property of a plastic workability

to the composites.

Now, These synthetic resins are composed of very large molecules. The particular

form and morphology will determine whether the plastic is a fiber, hard rigid

resin, or a rubber like product depending on this structure (we will get the final

rigidity of the composite.


polymerization

• process in which there occur a series of chemical reactions by which a polymer is formed from the monomer is known as polymerization.


• curing time would also affect the degree of polymerization, which is important. Clinically because the higher the mol. wt. the greater the stiffness. This stiffness is an important. Clinical requirement. (according to PROFFIT.)


Polymerization

• .Condensation polymerization.• .Addition polymerization.

• Condensation polymerization:

Condensation reactions result in polymerization plus the production of low molecular weight by products.


Addition polymerization :

• there is no change in composition during additionpolymerization.These macromolecules are formed from smaller. Units, or monomers, without change in composition, because the monomer and the polymer have the same empirical formulas. The structure of the monomer is repeated many times in the polymer.


STAGES IN ADDITION POLYMERIZATION

• Induction :

To start addition polymerization process, free radicals must be present. Free radicals can be generated by activation of monomer molecules with U.V. Light, visible light, heat or energy transfer from another compound that acts a free radical


• This free radical is known as the initiator. Most commonly employed initiator is benzyl peroxide which decomposes into 2 free radicals.

• Another term is activator. This activator activates the initiator of in turn this initiator initiates the polymerization.


• Thus, the process of polymerization can be activated in 3 ways.

• - Heat which activates this initiator.• Chemical – most commonly used is tertiary

amines (self-cure) • 2 are separated, when mixed then

polymerization begins. • light activated - here photons (of energy)

activate the initiator.


• Thus systems developed with visible light activated materials having a wave length of 470mm.

• In this system the initiation are camphorquinone and dimethylaminoethylmethacrylate (DMAEM)

• In this light intensity (therefore check machine) and distance for light source are important (therefore keep gun as possible with out touching)are important.


Propagation.

• Ideally, chains reactions should continue until all of the monomer has been converted to a polymer. However, the polymerization reaction is never complete.


Termination :

• Can take place in 2 ways. – Direct couping– Exchange of hydrogen atoms


Inhibition of polymerization.

• Impurities in the monomer, as stated, inhibit polymerization this impurity can react with the activated initiator or a growing chain, causing the inhibition.

• Eg. Hydroquinone is often added as an inhibitor in the monomer, to prevent polymerization during storage.

• More importantly the presence of oxygen also retards the polymerization reaction because oxygen reacts with the free radicals.

• Therefore we say that air thinning of bonding resins should be avoided to optimise curing.


Copolymerization :

• To custom design the physical properties of a polymer ,two or more chemically different monomers, each with some desirable property can be combined. The polymer thus formed is called a copolymer. And its process formation known as copolymerization , thus the polymer that would be formed would have properties intermediate to those of the individual monomers, depending on each components concentration.


TYPES OF RESINS :

• Acrylic resins : These imbibe water, this water tends to separate

the chains and to cause general softening and loss of strength.

- Methyl methacrylate. -Supplied as a liquid monomer and a powder these

are mixed to form a dough and then cured like in fabrication of dentures in prosthodontics.

-However, a volume shrinkage of 21% accurs during the polymerization of the pure methyl methacrylate monomer. This is too high.


• Polymethyl methacrylate.

It is hard resin with a high tensile strength. It does not discolor, but has a tendency to absorb water by imbibition.


• Multifunctional methacrylate systems.

-These include the bis GMA, TEGDMA and UEDMA which are used in composites and will be discussed later.


composition

• Consists of following components. • Resin matrix • Inorganic filler • Coupling agent. • Activator - initiator system. • Inhibitor • Other additives • Those to improve color stability • Pigments


Resin matrix.

• Bis GMA • UEDMA (Urethane dimethacrylate)• TEGDMA (Triethylene glycol dimethacrylate)


• The bis GMA have a high mol. Wt., but are very viscous at room temperature, the use of diluent monomers is essential to attain high filler levels and to use pastes of clinically usable consistencies. Diluents are usually TEGDMA However, the addition Of TEGDMA increases polymerization shrinkage, a factor that limits the amount of TEGDMA that can be used in a composite. Also TEGDMA increases crosslinking, which makes in material more resistant to degradation.


Filler Particles

• Filler particles commonly used silicon particles of colloidal size ranging from 0.1 to 100 um. Composites are often classified on the average size of the major filler component.

• In addition to filler volume, level, the size, the size distribution index of retraction, radiopacity and hardness are important in determining the properties and clinical application of resultant composites to incorporate maximum amount of filler. It is obvious that if a single particle, since is used, even with close packing, a space will exsists between particles consider filling a box with marbles.


• But on important Aspect of composites used in orthodontics it its fluidity. It should be fluid enough. So as to provide adequate micro mechanical inter locking the fluidity of the composite depends upon the fluidity of the resin and amount of filler. As the filler surface area increase this fluidity decreases. If there is a large amount of small particle filler then the surface area of the filler particle increases therefore we use composites with slightly large filler particle size.


• In order to ensure acceptable esthetics of a composite resin, the translucency of the filler must be similar to that of tooth structure becoming increasingly important in orthodontics with the advent of transparent bracket systems.

• The radiopacity it provided by a number of glasses such as barium, strontium and zirconium(Barium may leach out in saliva ?)


Coupling agent:

• It is important that the filler particles are bonded to the resin matrix, these allow the more flexible resin matrix to transfer stresses to the stiffer filler particles.this bond is provided by the coupling agent.

• The coupling agent, therefore, improves physical and mechanical properties and provides hydrolytic stability by presenting water from penetrating along the filler resin interface. Organosilanes such as r– methocryloxypropyl trimethoxy slane.

• (MOPTM ) 1s used most commonly. zirconates may also be used.


Activator initiator system. :

• This would depend on the type of composite used,

-Chemically or self cured.

-Light cured.


Self cured.

• Here the initiator is benzyl peroxide. • While the activator is a teritiaryamine(N-N

dimethyl-P-toulidine)


Light activated:

• Initially the light activated systems used UV light .• however, exposure to light at the correct wavelength

(approx. 468nm) produces an excited state of the photo initiator and an interaction with the amine to form free radicals that initiate addition polymerization.

• The commonly use photo initiator is comphorginone (C-0 has an absorption range b/w 400-500 mm that is in the blue region of the visible light spectrum.


Inhibitors

• To minimize or prevent spontaneous polymerization of monomers, inhibitors are added to resin systems. A typical inhibitor is butylated hydroxytoluene.


Optical modifiers:

• To match the appearance of teeth dental composites must have visual coloration (shading) and translucency that can simulate tooth structure.This is of importance when using transparent bracket systems. Shading is achieved by adding different pigments. These pigments often consist of metal oxides that are added in minute amount.


• All Optical modifiers affect the light transmission ability of a composite, darker shades and opacifiers should be placed in thinner layers to optimize polymerization. It is not of much clinical significance in orthodontics because we use a very thin layer of composite. However, it must be remembered this property may affect the cure of a bonding agent covered with a composite layer.


Curing :

• The first composites were cured by a chemically activated polymerization process, called cold curing. Cold curing is initiated by mixing two pastes.

• This had 2 disadvantages;• The operator had no control of the working time. • During the mixing process, it is almost impossible to avoid

incorporating air bubbles into the mix. Oxygen present hampers the polymerization.

• However, to over come these problems,materials that required no mixing were developed the light cure composites, where light is used for the activation of the initiator system.


• Advantages : • Insertion and proper placement of bracket can be completed

before starting curing. • Takes only 40 seconds for curing while self-cure may take

longer. • Also, these are no so sensitive to oxygen inhibition during

polymerization. • Drawbacks : • Tendency to shrink to towards the light source, resulting in a

pull back in areas away for light source. • Complicating factors associated with a light source.


• Modern light sources are hand-held devices that contain the light source. The light source is usually a tungsten halogen bulb. White light generated by the bulb passes through a fitter that removes the infrared and visible spectrum for wavelengths greater than 500nm. There can be a significant difference in the output for various manufactured lights. For example, if the light intensity manufactured by a factor of four then 80-40 seconds may be required for a low intensity light to achieve the same results as that produced by 20 to 60 second exposure with a high intensity light.

• When attempting to polymerize resin through a ceramic bracket, the exposure time should be 2-3 times longer, to compensate for the reduction in light intensity.


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• Light sources also generate different light intensities over time, depending on the quality of age of the lamp presence of contamination such as composite material residue on the light tip, and the composite. Consequently, the light source should be checked regularly and the operator should always place the light tip as close as possible to the restorative material.


• Composites are now available that combine cold curing and visible light curing components in the same material. These are available as two pastes, one contains benzyl peroxide and the other a tertiary amine. When the Clinician mixes the two pastes, and exposes them to light, both cold curing and light curing are achieved with the same material. These materials are called dual – cure materials.


• Polymerization stress initially is relieved by composite until it reaches the co-called “gel point” before this point the resin-based composite is flexible and accommodates to relieve stress. After this gel point is reached, the composite changes to an un-yielding state in which shrinkage stress is transmitted to the tooth structure. It has been observed that the longer the pre-gel point time, the less the stress in the past-gel phase.


• Now a days, high intensity energy out put light sources such as plasm arc curing lights or laser curing lights allow a reduction in polymerization rate. This results in a decrease of the pre-gel point time and may increase the shrinkage stress. Another concern is that some of these light sources presents narrow band of light emission may not correspond to the absorption band of the photo initiators, resulting in an incompletely cured resin. The operator should be cautious other using these alternate sources of light to polymerize resin-based composites.


CLASSIFICATION OF COMPOSITE

based on the size of the filler particles.

On this basis we have• Traditional - 8-12 um• Small particle -1-5 um• Microfilled -0.04-04um• Hybrid - 0.6-1.0um


PROPERTIES OF DIRECT BONDING RESINS.

• In light cured resins, the working time is that chosen by the operator Setting and working times.

• The setting times for chemically activated composite resin ranges from 3-5 minutes. Now composites are available with setting times of 60 seconds. This short setting time has been accomplished by control of the concentration of the initiator and accelerator., and the materials harden rapidly once they are exposed to curing light.


• . As mentioned earlier the depth of the cure is limited and is dependent on several variables such as material, color, location of light source and the quality of the light source. The resin paste should not be dispensed until it is to be used. Exposure to operatory lights for any appreciable time can initiate polymerization of the material, because these lights emit radiation in the 400-500nm range. About 75% of the polymerization takes place during first 10 minutes. The curing reaction occurs till about 24 hrs, until when optimum physical properties are not achieved.


Polymerization shrinkage

• Polymerization shrinkage occurs due to higher density of the polymer formed.

• Due to this polymerization shrinkage creates tensile stresses at the interface between the resin and the tooth. These stresses severely strain the bond create with a low-viscosity unfilled resin bonding agents against acid etched enamel at cavity margins and can lead to marginal leakage and early failure


• . It has been shown that this stress can exceed the tensile resistance of the enamel and result in stress resistance of the enamel and result in stress cracking and enamel fractures along the bonded interfaces. This potential for polymerization shrinkage is even greater for microfilled resins.


Thermal properties

• Coefficient of thermal expansion which gives us the amount of expansion per unit increase in the temperature.

• • Thermal diffusivity: how fast the heat spreads

within the resin.


WATER SORPTION

• Water sorption is greatly reduced in composites as compared to acrylic resins due to the bis-GMA and lower amount of resin.


SOLUBILITY

• Water solubility of composites depends on the resinous matrix more than the filler. The acrylic resins had higher solubility than the current composites. This was because the amount of residual monomer remaining


MECHANICAL PROPERTIES

• Plaque accumulation• In conventional composites for example,

which the resinous matrix wears out, the large particles project above the surface. This causes a roughening and results in increased plaque accumulation.

• The smaller the particle size, the lesser would he the plaque accumulation.


• Colour stability• This has gained importance due to the advent

of transparent bracket systems. As mentioned color stability would not be as good due to incomplete polymerization, due to water sorption and solubility. Otherwise, resins have observable change only over a 3 year period, which is more than sufficient for orthodontic treatment.


PRESENTATIONS

• These are available as

light cured

self cured composites.


MATERIAL SELECTION.

• According to Proffit.• The requirements of a bonding material are:

Dimensional stability. Adequate fluidity . Strength. Easy to use clinically. Less plaque accumulation.


GLASS IONOMER CEMENTS

• Glass lonomer cements are adhesive tooth colored restorative materials which were orignially used for restorations of eroded areas. Now, it has been modified to allow its use in other areas.


• The name of the cement is glass ionomer because, the powder is glass and the setting reaction and adhesive bonding to tooth structure is due to ionic bond.


synonyms

• Poly (alkenoate )cement• GLC (galss lonomer cement)• ASPA ( alumino silicate polyacrylic acid).


APPLICATION

• Anterior esthetic restorative materials for class III cavities

• For eroded areas and class V restorations• As a luting agent• As liners and bases• For core build up.• To a limited extent as pit and fissure sealant.


CLASSIFICATION

• Type I – For luting• Type II – For restorations• Type III – Liners bases.• (Some authors include Type IV-fissure

sealant, Type V- ortho-dontic cemtns and Type VI-core build up as part of the classification).


COMMERCIAL NAMES

• Aquacem, Fugi I – Type I • Chem Fil - Type II• Ketac bond - Type III• Vitra bond - Light cure


AVAILABLE AS

• Power/liquid in bottles• Pre-proportioned power/quid in capsules• Light cure system• Powder/distilled water (water settable type)


composition

• POWDER

silica

alumina

Al flouride

Ca flouride

Na flouride

Al PO4


• LIQUID:

poly acrylic acid

tartaric acid

water


Setting reaction : :

• When the powder & liquid are mixed together, the acid liquid attacks the glass particles. Thus calcium, aluminium, sodium and flouride ions are leached into the aqueous medium, probably in the form of complexes.

• Calcium polysalts form first and later aluminium polysalts cross link the polynion chains.

• The salts hydrate to form a gel matrix, and the unreacted glass partcles are covered by a silica gel which arises from removal of cations from the surface of the particles.


• Adhesion : • GICs bonds chemically to tooth structure.

The bonding is due to the reaction between the carboxyl groups of the polyacids and the calcium in the enamel.


• Anticariogenic properties : • Glass ionomer releases flourides and

continue to do so over an extended period of time.

• In addition due to its adhesive effect they have the potential for reducing infiltration of oral fluids at the cement – tooth interface, thereby preventing secondary caries.


Resin modified glass ionomer:

• These are relatively new materials having various names like compomer, resin – inomers, RMGI, light cured GIC, dual cure GIC and tricure GIC.


Classification :

• Depending on which is the predominant component. These materials may be classified as (Mc Clean et al).

• Resin - modified glass ionomers cement (RMGI), e.g. Fuji II LC, Vitremer, Photac fil.

• Poly acid – modified composites (PMC), e.g. Dyract, Variglass VLC.


Composition :

• The powder contains. • Ion leachable glasses (silica, abumina)• Photointiators or chemical intiators or both• Polymerizable resin.


The liquid contains • Polyacrylic acid. • Water.• Methacrylate monomer • Hydroxyethyl methacrylate monomers.


Properties :

• Strength :

The compressive strength is slightly lower 105 Mpa when compared to conventional GIC. The diametral tensile strength is however, greater 20 Mpa because of the plastic nature of the resin component.


• Hardness:

The hardness 40 KHN is comparable to that of conventional GIC.


• Adhesion :

The bonding mechanism to tooth structure is similar to that of conventional GIC. Micromechanical retention also plays a role in the bonding process.


• Anticariogenecity :

These materials have a significant anticariogenic effect because of the fluoride release.


• Esthetics : They are less translucent because of the significant differences in the refractive index between the resin matrix and powder particles.


• GIC:- variety of compositions and changes in the evolution of glass ionomers materials.


1) Traditional GIC (lines, bases, cements)

Modified by adding comonomers to polyacrylic acid small powder particle size.

2) Metal modified glass ionomer Miracle mixtures (with Ag alloy admixed with cement)

Cement particle reinforced.


3) LC GIC (linen, bases)

HEMA added to liquid component;monomers in liquid modified with acrylic functional groups.

Other powder particles mixed with alumino-silicate glass


4) Hybrid (resin modified ) GIC

-Silicate glass of composite substituted for some of powder component.

-Polymer and other phones added to powder component .

-HEMA and other monomers added to liquid component.

-Pre cured GI blended into composites


6) Polyacid – modified resin composite (component)

cements, restorative filing materials, cores

-methacrylate monomers which multiply carboxylic groups; addition of ion leachable glass (as in a conventional glass ionomer).


Acid – Etching :

• Objectives :

1. To remove all debris and pellicle to increase adaptation of resin.

2.Dissolution of exposed ends of enamel rods.

3.Create surface irregularities that increase surface area for increased bond strength.


Mechanism :

1.Acid solution affects prismatic structure by preferential removal of either prism core / periphery .

• 2.Adsorption of highly polar phosphate groups oil the enamel surface, e the result strong polar bonding to the acrylic may result.

• 3.Removal of old, fully reacted and inert enamel surface exposing a fresh, reactive surface more favorable for adhesion.

• Tremendous increase in surface area / wettability.


EFFECTS OF ACID ETCHING ON SURFACE ENAMEL:

• Type 1 Etching pattern:

Prism core material is preferentially removed, leaving the prism peripheries relatively intact, resulting in a “honeycomb” appearance.


• Type 2 Etching Pattern

The peripheral regions of the prisms are dissolved preferentially, leaving the prism cores relatively intact resulting in a “cobblestone” appearance


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• Type 3 Etching Pattern : Surface loss occurs without exposing the

underlying enamel prisms. Gwinnett (1971) demonstrated that this etching pattern is usually observed at the cervical aspects of teeth where the enamel prisms do not extend to the surface.

-Denys and Retief (1982) showed however, that the type 3 etching pattern is not confined o the cervical regions but is also found on other aspects of an etched enamel surface.


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• Silverstone (1974) showed that etching enamel surfaces with phosphoric acid resulted in ;

• A superficial etched zone • Under lying qualitative and quantitative

porous zones.


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– The depth of the etched zone or the amount of the surface enamel removed during the etching procedure depends on ;

– The acid concentration– The duration of etching – The chemical composition of the surface enamel.


• The surface area of the enamel will increase upto 2000 times that of its original unetched surface area.

• 4. It creates valleys and depressions and makes the enamel surface irregular at an average depth of 25 microns.

• 5. Acid etching will expose proteinaceous organic matrix substance of enamel, which can add to the restorations retention if it becomes adequately embedded within the restorative material.


• . It has been verified that enamel treatment with phosphoric acid will add to the enamel surface a highly polar phosphate group, which will increase the adhesive ability of the enamel surface.

• Several acidic agents have been evaluated by various investigators like lactic acid, citric acid, pyruvic acid Alpha-keto acarboxylic acid other than the phosphoric acid.


• Brauer and Termini (1972) reported that lactic acid, a Monohydroxycarboxyic acid was an effective adhesion promoter.

• Cadwell and Johannessen (1971) investigated the possible use of citric acid as an etching agent. Citric acid solutions are now being used to condition tooth surfaces


• Pyruvic acid and a Alpha – Ketocarboxyolic lead to good bond strengths when used for etching the enamel surface.

• Rate of etching of enamel by pyruvic acid was significantly lower than that with 50% H3PO4.

• The concern about the stability of pyruvic acid solutions has limited the use of pyruvic acid as an enamel etchant.


Classification of Adhesion:

• Physical bonding • Chemical bonding• Mechanical bonding


REQUIREMENTS FOR ADHESION

• There must be good wetting in order to produce a good bonding.

• the surfaces being joined should to produce and maintain. Clean surfaces are at a high energy state and rapidly absorb contaminants such as the moisture or dust. If the contaminants are not excluded, the adhesive interface will be weak.


CLINICAL FACTORS AFFECTING ADHESION

• Salivary and/or blood contamination.• Moisture contamination from handpieces or

air-water syringes.• Oil contamination from handpieces or air-

water syringe.• Surface roughness of tooth surface• Fluoride content of teeth.• Presence of plaque, calculus, extrinsic stain

or debris


FACTORS AFFECTING ADHESION TO MINERALIZED TISSUE

• as given by Gwinnet (1990). • Physical and chemical properties of the

adhesive and the adherent. • Lack of homogeneity between them. • Manner of transmission of the applied loads

through the bonded joint. • Thickness of the interface. • Form of surface pretreatment or primer

chosen for the substrate


• Furthermore, the factors related to the oral environmental

• Moisture• Physical stresses • Changes in temperature • Changes in pH• Dietary components • Chewing habits.


Chemistry of Adhesive agent

• Chemical adhesion • Adhesion by coupling agents • Adhesion by grafting reaction


CRYSTAL GROWTH ON THE ENAMEL SURFACE

• An alternative to the conventional phosphoric and etch technique has been developed by R. Maijer and D.C. Smith.

• This system consists of a polyacrylic acid treatment, liquid containing a sulfate component that reacts with the calcium in the enamel surface to form a dense growth of small, needle – shaped crystals.


• These crystals grow in so called spherulitic habit

• The crystal buildup on the enamel serves as an additional retentive mechanism for the resin that bonds to the tooth surface. In this procedure the bond does not rely on extensive penetration into the enamel. This brings about “micromechanical interlocking” at the enamel surface.


MICRO AIR ABRASION

• An alternative to acid etch• In 1943 Dr. ROBERT BLACK began his studies

using micro abrassive.• In 1951 an air abrassive instrument was

introduced(Airdent)


• This technique used high speed stream of purified aluminium oxide (alpha alumina) particles propelled by air pressure.


BONDING PROCEDURES

• bonding of orthodontic attachment offers several advantages when compared to conventional banding.

• It is esthetically superior • Faster and simple.• Less discomfort for patient (no. bond seating

and separation


• Arch length not increased by band material • Allows more precise bracket placement

aberrant tooth shape does not result in difficult bonding and poor attachment position )

• Improve gingival condition is possible and there is better access for cleaning.


• Partially erupted tooth or and fractured tooth can be controlled.

• Mesiodistal enamel reduction is possible during • Interproximal areas are accessible for composite

buildups. • Caries risk under loose bonds is eliminated.

interproximal caries can be detected and treated. Dental invaginations on incisors can be controlled.


• No band spaces at the end of Rx to close• No large supply of bands is needed.


• Attachments may be bonded to fixed bridge work, particularly when the facial surfaces of the abutment teeth are not in metal.

• More hygienic. • Improved appearance • Discomfort to patient is decreased. • Ease of application for clinician.


Disadvantages :

• Bonded bracket has a weaker attachment than a cemented band. Thus there is more chance that a bracket will come off rather than a band become loosened.

• Some bonding adhesives are not sufficiently strong.

• Better access for cleaning does not necessarily guarantee better oral hygiene and improved gingival condition, especially if excess adhesive extends beyond the bracket base.


• Protect against interproximal caries of well contoured cemented bands is absent.

• Bonding is generally not indicates on teeth where lingual auxiliaries are required or where headgears are attached.

• Rebonding a loose bracket requires more preparation than rebanding or loose band.


• Debonding is more time consuming than debanding therefore removal of adhesive is more difficult than removal of cement.


Bonding procedure :

• Cleaning

• Enamel conditionong

• Sealing

• Bonding


SEALANT

• A CONTROVERSY


Bracket bonding procedure.

• TRANSFER

• POSITION

• FITTING

• REMOVAL OF EXESS


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Type of adhesives :

• ACRYLIC RESINS

• DIACRYLATE RESINS


• ACRYLIC RESINS • Eg; Orthomite , Directon, Bondeze, genie. • Based on self curing acrylics • MMC monomer + ultrafine powder


• DIACRYLATE RESINS• Based on acrylic modified epoxy resin

Bowen’s resin or BisGMA may be polymerized by cross linking in to 3-D network..

• Filled • Unfilled


• Buzzitha etal 82 found that a highly filled diacrylate resin with large filler particles gave the highest values of in vitro bond strength for metal brackets.


Two recent innovations

• No mix adhesive

Rely a Bond,Right On,System1

• Visible light-polymerized adhesives

Fotofil, Durafil


Key to good success in bonding

• . Develop a technique that ensure good moisture control .

• Fit the brackets closely to the teeth • Be sure that the setting of the adhesive is

undisturbed • Use a strong adhesive.


G.I.C Bonding

• Introduced by Wilson and Kent ‘’71• IN 1986 ‘ White described a method of

bonding ortho brackets to and surfaces of teeth with GIC.

• Cook ‘ 90 Compared in vivo bond strength of GIC with composite and concluded that bond strength of GIC was not nearly as good as that of resin


• Fajen etal ’90 evaluated bond strength of 3 GIC against composite in vitro and like look included that their bond strength was significantly less.

• Compton etal ’92 : • Compared bond strengths of GIC, stated

that they must not be contaminated by moisture during bonding procedures. In addition they suggested


• Fricker ‘ 94 : • Worked with fuji similar LC GIC and found

same rate of success as that of composite. He did mention however that a dentine conditioner was utilized for10sec, then rinsed followed by lightly drying the tooth surface before bonding the brackets with GIC.


• Kusy ‘ 94 : • Discussed the damage to the teeth when

debonding techniques are used for removing composite. He advocated the use of GIC for orthodontic bonding procedures. Because their cements do not need etching or cause damage during debonding.


Advantages :

• Saves a significant amount of chair time • Eliminates need for working in dry field. • Eliminate need “ etching and priming enamel

surface • Fluoride release protects teeth against

decalcification • Repairs are quick and easy.


• Patient operator comfort. • Reduced risk of caries. • Have capacity to absorb Fluoride from

fluoridated tooth paste, thus acting as a rechargeable sow release Fluoride device (long term Fluoride releasing agent.)


REVIEW OF LITERATURE

• Direct bonding of brackets using shorts etching times.

• Wolf gang castensen : 1986 JCO.• They concluded that the shorter etching time

of 15 seconds appears to be sufficient for the bracket bonding


• Russull Bert Forquhar – 1986 AMJO. • -Share bond for phosphoric acid was greater

than polacrylic acid group.


• . Dual Cement resin in bonding : • Smith and Shivapuja.• a dual cement, they can be used where the

depth of cure is essential.


• Oslenetal compaired the shear bond strength and surface structure between conventional acid etching and air – abrasion of human enamel. And concluded Air abrasion technique for enamel preparation has lower and clinically un acceptable shear bond strength and this technique for enamel preparation results in the irriversible removal of both the inorganic and organic component of enamel matrix and said that air abrasion of enamel surface orthodontic brackets is not advocated for routine clinical use at this time. AJO – 1997 – vol 112.


• Comparison of GIC a composite AJO 1995 May (485-487)

• Miguel, Almeida and Chapel. • They studied that composites showed a

statistically significant lover failure rate compared to the GIC.


• Roberts-Harry (1992) used a pulsed Nd:YAG laser to etch the enamel surfaces of teeth in vivo prior to the bonding of orthodontic brackets with composite resin and concluded that this laser produced a macroscopic etch pattern similar to that found with acid etching


• J.A. Vonfraunhofer et al (1993)

• Arcoria .C.J., Lippas M.G. and Vitasek B.A., (1993)


ADHESION BOOSTER

• Hypocalcifed • Fluorsed • Exessive chalky• Decidous enamel• The do not present ideal surface for bonding• ENHANCE ADHESION BOOSTER


THANK YOUFor more details please visit



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