1

Principles of bonding and adhesives in dentistry

Dental materials

2

What is adhesion?

The force that binds two dissimilar materials together when they are brought into intimate contactIn dentistry, bonding refers to the process of attaching a restorative material to tooth structure by adhesion

3

Basic principles in the bonding process

Surface preparation to remove plaque & debrisAcid etching with phosphoric acid, to remove mineral, create porosity, wettabilityBonding agent applied and flows to fill the porosities and create resin tags (micromechanical retention)Resin applied and bonds chemically to underlying bonding agent (primary bonding)

4

Adhesion

For proper adhesion to occur, intimate contact between the adhesive and the substrate is needed. This intimate contact is affected by:Wettability of the substrate surfaceThe viscosity of adhesiveThe morphology or surface roughness,

5

Factors affecting adhesion

1. Wettability and surface energy

High surface energy low surface energy (solid)

Surface energy: the attraction of atoms to a surface (directed inward). In liquids, it is called surface tension

liquidθ

solid solid

liquidθ

6

Continue,

2. Viscosity of bonding agent

3. Interpenetration (formation of hybrid zone)

4. Micromechanical interlocking

5. Chemical bonding

7

8

9

Isolation

10

Enamel etching

Introduced by Michael Buonocore in 1950sEtching time: 10-30 seconds (around 15 seconds)Primary teeth and fluoride treated teeth require more timeEtched enamel looks frosty white when driedEtching produces a rough surface (pits) into which resin flows and forms resin tags = micromechanical retention

11

Enamel etching

Resin tags may penetrate to a depth of 10-20 microns in etched enamelThe depth of penetration depends on:

Etching timeRinsing time

These two actors determine how effective etching was, and how well debris were removed from enamel surface

12

Enamel etching

Without etching, bonding is weakened and this leads to microleakage

In amalgam corrosion products may seal any spaces between cavity and restoration, in GIC the release of fluoride provides protection but in composite, good bonding is essential.

13

Enamel etching

Liquid or gel (the gel is made by adding colloidal silica to the acid) phosphoric acid 30-50% (usually 37%).

14

Procedure

Acid etch is applied using a brush or, if acid is supplied in disposable syringes, the acid maybe applied directly out of the syringe tipEtchant is applied for 15 seconds, or longer is mentioned previously

15

Before etching

Acid etching gel

After etching

16

Procedure continue,

Rinsing is done with water for 20 seconds then dried well. It should have a frosty white appearanceEnamel should be kept clean and contaminant free (saliva, blood, etc)If contamination occurs enamel should be re-etched for 10 seconds

17

Enamel bonding

In the past, etching and bonding involved only enamel. Currently, total etch technique is done, and bonding agents are applied to both enamel and dentine.Bonding agents used for enamel bonding were made from resin combined with diluents to lower viscosity. (Bis-GMA + TEGDMA)

18

Dentine etching and bonding

What makes dentine a challenge when it comes to adhesive bonding:

Dentine is a living tissue (50% HA, 30% collagen, 20% fluid)Tubular nature of dentine (dentinal fluid)Branching patterns in tubules, may enhance retentionSmear layer presencePossible side effects on the pulp

19

Dentine etching

1979 etching was done for dentine as well as enamel using 37% phosphoric acid. Research proved enhanced bonding (total etch technique)Over etching will remove more mineral than needed and open up tubules, and expose more collagen, making dentine more difficult to coat with bonding agentOver etching dentine leads to weaker bond and sensitivityOver drying should be avoided to prevent collapse of collagen and occluding tubules

20

Continue,

Another study showed how resin tags from bonding agents in dentine infiltrated a surface layer of collagen in demineralized dentine to form the HYBRID LAYER

21

22

23

Bonding agents

Several years ago, it was believed that bonding to dentine can be achieved by chemical bonding between resin and either collagen or mineral content of dentine. Molecules designed for these purposes had the following presentation: M-R-X: M is a methacrylate group, R is a spacer such as hydrocarbon chain (ensure mobility of M group when X is immobilized), an X is a functional group that can bond to calcium in HA (usually an acidic group)

24

Generations of bonding agents

First generation (1950s): based on silane coupling agents model. Based on M-R-X model:

M=methacrylate groupR= hydrocarbon groupX= glycerolphosphoric acid dimethacrylate

Success rate was low, due to high polymerization shrinkage and high CTE in unfilled resins used in those time

25

Bonding agents

Second generation ( late 60s early 70s): similar concept to first generation agents. Low success rate. Attempts were made to deal with the smear layerThird generation agents: same as the previous generation, however attempts were made to modify or remove the smear layer which consists of:

26

Bonding agents

Smear layer: it is weakly bonded t dentineDentine particlesBacteriaSalivary constituents.

Procedure in 3rd generation agents:Application of dentine conditioner (HEMA, or 2% nitric acid, or maleic acid)Application of primer (dentine bonding agent based on M-R-X)Application of adhesive (unfilled resin)Placement of resin composite

27

28

Bonding agents

Fourth generation: procedure, Total etch technique for enamel and dentine, dentine conditioned for 15 seconds. Rinsing with water follows, then gentle drying without desiccating dentine to prevent collapse of collagen fibersRinse to remove etchant and demineralized debrisDry to ensure enamel is etchedSlightly moisten dentineAbsorb excess water with cottonApply hydrophilic primer (contains resin that polymerizes within collagen and a solvent that evaporates to ensure drying of tooth surface). Apply adhesive (bonding resin) then cureComposite applied and cured

29

Bonding agents

Fifth generation agents: fewer steps, better results. Rely on micromechanical retention involving:

Penetration into partially opened dentinal tubulesFormation of hybrid layer (hydrophilic monomer penetrate and polymerize to form interpenetrating network with collagen fibrils

30

Generations of bonding agents

Fifth generation bonding agents:

Etching is achieved using phosphoric acid.Priming and bonding is combined in one step.

31

Continue,

Self-etching primers Acidic groups are added to etch tooth surfaceNo need for rinsing and dryingMay not be effective on unprepared enamel

Self priming adhesive: most commonly used now

32

Continue,

Fifth generation agents:Self etching primers applied then driedFollowed by bonding agent application

UniFil bond from GC Corp.

Adper SE scotchbond adhesive (self etch primer and adhesive

33

34

Bonding

Bonding agentCuring

35

Microleakage

Occurs when the restoration does not completely seal the surrounding margins of the cavity preparation

Possible outcomes of microleakage?

What contributes to microleakage?

36

37

Factors that prevent good bonding

38

Measurements of bond strength

Tests used:Shear bond strengthTensile bond strength

Data were variable due to variability of tooth surface, and different testing methods

Microtensile and microshear bond strength: less variability.

39

Amalgam bonding

Older amalgam restorations leak less due to corrosion productsTechnique:

Cavity preparation then isolationEtching of enamel and dentine to remove smear layerPrimer applied and curedSelf-cure bonding resin applied then amalgam is applied

40

Clinical applications of bonding

Porcelain bonding and repair involves:SandblastingSpecial etchant (hydrofluoric acid)Silane applied for 30 seconds then dried to evaporate solvent (leaving a layer of vinyl that bonds resin to adhesive)Bonding agent appliedComposite applied

41

Pit and fissure sealants

Filled and unfilled resinsGICSuccess depends on good wetting, intimate contact through etching which will also ensure longevity of the sealant.PRR: minimal cavity preparation, resin composite placement, sealant placement on top.

42

Glass ionomer cements bonding

31 2

4 5

43

Thank youReference,

Philips science of dental materials, Chapter 14Dental materials, clinical application for dental assistants and dental hygienists, pages: 44 (dentine etching),48-50 (microleakage, factors that prevent good bonding, porcelain, amalgam bonding)Chapter 5