Lecture 7 & 8- Bonding and Adhesives (Slides)

8/3/2019 Lecture 7 & 8- Bonding and Adhesives (Slides)

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Principles of bonding and

adhesives in dentistry

Dental materials


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What is adhesion?

The force that binds two dissimilar materials

together when they are brought into intimatecontact

In dentistry, bonding refers to the process of

attaching a restorative material to tooth

structure by adhesion


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Basic principles in the bonding

process

Surface preparation to remove plaque & debris

Acid etching with phosphoric acid, to remove

mineral, create porosity, wettability Bonding 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)


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Adhesion

For proper adhesion to occur, intimate

contact between the adhesive and the

substrate is needed. This intimate contact isaffected by:

Wettability of the substrate surface The viscosity of adhesive

The morphology or surface roughness,


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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

liquid

solid solid

liquid


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Continue,

2. Viscosity of bonding agent

3. Interpenetration (formation of hybrid zone)

4. Micromechanical interlocking

5. Chemical bonding


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Isolation


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Enamel etching

Introduced by Michael Buonocore in 1950s

Etching time: 10-30 seconds (around 15seconds)

Primary teeth and fluoride treated teeth

require more time Etched enamel looks frosty white when dried

Etching produces a rough surface (pits) intowhich resin flows and forms resin tags =micromechanical retention


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Enamel etching

Resin tags may penetrate to a depth of 10-20

microns in etched enamel The depth of penetration depends on:

Etching time

Rinsing time

These two actors determine how effective

etching was, and how well debris wereremoved from enamel surface


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Enamel etching

Without etching, bonding is weakened and

this leads to microleakage

In amalgam corrosion products may seal anyspaces between cavity and restoration, in

GIC the release of fluoride provides

protection but in composite, good bonding isessential.


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Enamel etching

Liquid or gel (the gel is

made by adding

colloidal silica to the

acid) phosphoric acid

30-50% (usually 37%).


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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 tip

Etchant is applied for15 seconds, or longer is

mentioned previously


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Before etching

Acid etching gel

After etching


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Procedure continue,

Rinsing is done with water for 20 seconds

then dried well. It should have a frosty whiteappearance

Enamel should be kept clean and

contaminant free (saliva, blood, etc)

If contamination occurs enamel should be re-

etched for 10 seconds


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Enamel bonding

In the past, etching and bonding involved

only enamel. Currently, total etch technique isdone, 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)


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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

retention

Smear layer presence

Possible side effects on the pulp


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Dentine etching

1979 etching was done for dentine as well asenamel using 37% phosphoric acid. Researchproved enhanced bonding (total etch technique)

Over etching will remove more mineral than neededand open up tubules, and expose more collagen,making dentine more difficult to coat with bondingagent

Over etching dentine leads to weaker bond andsensitivity

Over drying should be avoided to prevent collapseof collagen and occluding tubules


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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


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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)


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Generations of bonding agents

First generation (1950s): based on silane

coupling agents model. Based on M-R-Xmodel:

M=methacrylate group

R= hydrocarbon group

X= glycerolphosphoric acid dimethacrylate

Success rate was low, due to highpolymerization shrinkage and high CTE in

unfilled resins used in those time


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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 layer

Third generation agents: same as theprevious generation, however attempts were

made to modify or remove the smear layerwhich consists of:


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Bonding agents

Smear layer: it is weakly bonded t dentine

Dentine particles

Bacteria

Salivary 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


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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 preventcollapse of collagen fibers

Rinse to remove etchant and demineralized debris

Dry to ensure enamel is etched Slightly moisten dentine

Absorb excess water with cotton

Apply hydrophilic primer (contains resin that polymerizes

within collagen and a solvent that evaporates to ensuredrying of tooth surface).

Apply adhesive (bonding resin) then cure

Composite applied and cured

B di


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Bonding agents

Fifth generation agents: fewer steps, better

results. Rely on micromechanical retentioninvolving:

Penetration into partially opened dentinal tubules

Formation of hybrid layer (hydrophilic monomerpenetrate and polymerize to form interpenetrating

network with collagen fibrils

G i f b di


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Generations of bonding agents

Fifth generationbonding agents:

Etching is achieved

using phosphoric acid.

Priming and bonding is

combined in one step.

C i


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Continue,

Self-etching primers

Acidic groups are added to etch tooth surface No need for rinsing and drying

May not be effective on unprepared enamel

Self priming adhesive: most commonly used

now

C i


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Continue,

Fifth generation agents:

Self etching primers

applied then dried

Followed by bonding

agent application

UniFil bond from GC Corp.

Adper SE scotchbond adhesive(self etch primer and adhesive


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B di


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Bonding

Bonding agentCuring

Mi l k


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Microleakage

Occurs when the restoration does not

completely seal the surrounding margins ofthe cavity preparation

Possible outcomes of microleakage?

What contributes to microleakage?


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Factors that prevent good bonding


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Factors that prevent good bonding

Measurements of bond strength


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Measurements of bond strength

Tests used:

Shear bond strength Tensile bond strength

Data were variable due to variability of tooth

surface, and different testing methods

Microtensile and microshear bond strength: less

variability.

Amalgam bonding


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Amalgam bonding

Older amalgam restorations leak less due to

corrosion products Technique:

Cavity preparation then isolation

Etching of enamel and dentine to remove smear

layer

Primer applied and cured Self-cure bonding resin applied then amalgam is

applied

Clinical applications of bonding


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Clinical applications of bonding

Porcelain bonding and repair involves:

Sandblasting Special etchant (hydrofluoric acid)

Silane applied for 30 seconds then dried to

evaporate solvent (leaving a layer of vinyl thatbonds resin to adhesive)

Bonding agent applied

Composite applied

Pit and fissure sealants


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Pit and fissure sealants

Filled and unfilled resins

GIC Success 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 ontop.

Glass ionomer cements bonding


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Glass ionomer cements bonding

31 2

4 5


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Thank youReference,

Philips science of dental materials,

Chapter 14

Dental materials, clinical application fordental assistants and dental hygienists,pages: 44 (dentine etching),48-50

(microleakage, factors that prevent goodbonding, porcelain, amalgam bonding)

Chapter 5

Lecture 7 & 8- Bonding and Adhesives (Slides)

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