bonding and adhesives (1)

7/31/2019 Bonding and Adhesives (1)

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Principles of bonding andadhesives in dentistry

DENTAL MATERIAL II

DONE BY: EYAD MASSALHA


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What is adhesion?The force that binds two dissimilar materials together when they are brought

into intimate contact. In dentistry, bonding refers to the process of attaching arestorative material to tooth structure (enamel and dentine) by adhesion.

Basic principles in the bonding processSurface preparation to remove plaque & debris, we need some sorts of

preparation to the tooth surface to make bonding process, and the surface of thecavity should be clean from any remnant of tooth structure. Some principle

preparation should be done to remove any plaque and debris any contaminanton the surface.

Acid etching with phosphoric acid IN CASE OF COMPOSITE, to removemineral of the tooth structure, create porosity, enhance wettability.Wettability should be good enough to ensure good results. It will cover a larger

surface area between the surface and the filling, we will have better bondingforce.

Wettability is the ability of a liquid to maintain contact witha solid surface, resulting from intermolecular interactions when thetwo are brought together. The degree of wettability is determined by a

force balance between adhesive and cohesive forces.

Phosphoric acid will create pores and roughness of the surface and increase the

wettability, so anything you place on the top it, will flow much better. After that

when the bonding agent is on the surface, the composite will stick with it withthe tooth structure.

Bonding agent applied and flows to fill the porosities and create resin

tags (micromechanical retention). We dont need the material to be tooviscose otherwise it will not flow well, and the morphology of the tooth structureis important, a rough surface provide better adhesion than the smooth surface.

THE ROUGHNESS CREATED BY PHOSPHORIC ACID.Will remove part of the minerals in the enamel and dentin and also it will removepart of the mineral in the dentinal tubules open them create the micro -pores.

Without the roughness there will be no good bonding.

Resin applied and bonds chemically to underlying bonding agent

(primary bonding).
http://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Surfacehttp://en.wikipedia.org/wiki/Intermolecularhttp://en.wikipedia.org/wiki/Adhesionhttp://en.wikipedia.org/wiki/Cohesion_(chemistry)http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Cohesion_(chemistry)http://en.wikipedia.org/wiki/Adhesionhttp://en.wikipedia.org/wiki/Intermolecularhttp://en.wikipedia.org/wiki/Surfacehttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Liquid


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AdhesionFor proper adhesion to occur, intimate contact between the adhesive

and the substrate is needed. This intimate contact is affected by: Wettability of the substrate surface, should be good enough The viscosity of adhesive should be low viscosity to flow and cover

much surface as possible. The morphology or surface roughness, as you know a rough surface

provide better adhesion.

Factors affecting adhesion

This factors affecting the bonding between the restorative material andthe tooth structure. We need to look about factors related to the toothstructure and the adhesive material itself (combination of factors) to

make a bonding process.

Wettability and surface energySurface energy: the attraction of atoms to a surface (directedinward). In liquids, it is called surface tension. So its related to

surface tension of the liquid (adhesive) and surface energy of the solid(tooth structure), when apply acid etching will modify the surface energy(enamel and dentin) making them good wetted. For good results, should

be high surface energy and low surface tension.When the wettability isboor, the liquid form droplet and high contact angel. But when thewettability is good, the liquid flows better and able to wet the surfacemore and low contact angel.

Viscosity of bonding agent Interpenetration (formation of hybrid zone), how the bonding agent

penetrate inside the tooth structure.

Micromechanical interlocking Chemical bonding

Clinical application

ISOLATIN, ETCHING, BONDING.After a cavity preparation we need good isolation to the tooth from asurrounding environment like blood, saliva and any contamination.

Following by etching to enhance the cavity surface by acidic material.


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In amalgam corrosion products may seal any spaces between cavityand restoration, some elements of corrosion products can accumulate between

the tooth structure and amalgam and close the gap, prevent the microleakage tooccur. Corrosion means part of the amalgam will start to break down ordissolve.

In GIC the release of fluoride provides protection, and also the GIC bindto the tooth structure chemically so no gap between the tooth and GIC and no

microleakage.

But in composite, good bonding is essential, while the composite sitting,shrinkage will occur then microleakage, so good bonding isvery important forcomposite.

Liquid or gel (the gel is made by adding colloidal silica to the acid)phosphoric acid 30 - 50% (usually 37%). How did they come up with this

percentage? they tried different percentages, they examined the bond strengthof the material with the enamel & dentine, and see which is better, which onegives you the better bond strength.

Procedure

Acid etch is applied using a brush or, if acid is supplied in disposablesyringes, the acid maybe applied directly out of the syringe tip. The acidetching, blue or green in color, a gel is provided, a liquid also can be available,

but the gel is better because it will not flow everywhere and it's easier to control

it.

Etchant is applied for 15 seconds, or longer as mentioned previously.

Rinsing is done with water for 20 seconds then dried well, to ensure thatyou have removed all the acid. We use the water to rinse, but also we need touse some force to make sure that the surface is clean so we use water with air.

It should have a frosty white appearance.

Enamel should be kept clean and contaminant frees (saliva, blood, etc).

If contamination occurs enamel should be re-etched for 10 seconds.


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Enamel bondingIn the past, etching and bonding involved only enamel. Currently, total

etch technique is done, and bonding agents are applied to both enameland dentine. Today bonding agents are applied to both enamel and dentine sowill provide a strong bonding with the restorative material.

Bonding agents used for enamel bonding were made from resincombined with diluents to lower viscosity, (Bis-GMA & TEGDMA). The

lower viscosity to ensure flow the material very well.

Dentine etching and bondingWhat makes dentine a challenge when it comes to adhesive bonding?

Dentine is a living tissue (50% Hydroxylapatite, 30% collagen,20% fluid).

Tubular nature of dentine (dentinal fluid). Branching patterns in tubules, may enhance retention, the tubules

form a pathway to the pulp. Smear layer presence. Possible side effects on the pulp.

Dentin is different from enamel, and it contains minerals, collagen, dentinaltubules, fluids, nerves extended into the pulp. So you need to be careful whenyou etch it or deal with it, and need special treatment.

1979 etching was done for dentine as well as enamel using 37%

phosphoric acid. Research proved enhanced bonding (total etchtechnique). Total etch technique mean, the etching include both enamel anddentine.

Over etching will remove more mineral than needed and open uptubules, and expose more collagen, making dentine more difficult tocoat with bonding agent.

Over etching dentine leads to weaker bond and sensitivity. When we

come to etch the dentine, we should avoid over etching time, because we willremove more minerals and open the tubules more and more lead to irritation totubular fluid by action of the acid, then will stimulate the nerve ending and causesensitivity to the pulp and pain. So dont etch the dentine more than 15 sec.


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Over drying should be avoided to prevent collapse of collagen andoccluding tubules. Making dentine more difficult to coat with bonding agent.

To prevent over drying, after we finishing from etching, clean the surface thendehydrate it from any excess of water, then take small cotton put water on itand place it on the cavity surface to prevent collagen collapse.

Over etching and over drying will weaken the bond and causesensitivity to the patient.

Another study showed how resin tags from bonding agents in dentine

infiltrated a surface layer of collagen in demineralized dentine to formthe HYBRID LAYER. This layer as intermediate layer thats bond composite toenamel and dentine. The hybrid layer should be covering all cavity surfaces to

ensure a good bonding. So the hybrid layer attached to composite at one endand the tooth structure at another end. Its sticks to the tooth micromechanicallyand the composite attached to the hybrid layer chemically since both of them are

made of resin.

Bonding agentsSeveral years ago, it was believed that bonding to dentine can beachieved by chemical bonding between resin and either collagen or

mineral content of dentine.

Molecules designed for these purposes had the following presentation

MRX.

M is a methacrylate group (hydrophobic and can attach itself to the resin).

Ris a spacer such as hydrocarbon chain (ensure mobility of M group when X isimmobilized).

Xis a functional group that can bond to calcium in hydroxyapatite (usually anacidic group) which is hydrophilic.

Earlier bonding agents based on silane coupling agents, as in composite wetalked about something we called filler and matrix, it's called silane couplingagents, it has hydrophilic end that capture the filler and hydrophobic end that

capture the resin matrix and we called it to the resin. Same thing in composite

applied to bonding agents, so we want something to have an end orrepresentation by X for example that will capture mineral content from

hydroxyapatite and another end or another type of molecule that hold oncollagen or organic component in dentine, so it can place both on enamel anddentine hold on to them then composite can be added and it can be chemically

added.


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Generations of bonding agentsFirst generation (1950s): based on silane coupling agent model. Based

on M-R-X model, success rate was low, due to high polymerizationshrinkage and high CTE in unfilled resins used in those times. The CTEshould be similar to enamel and dentine to prevent shrinkage or expand the

material. The first generation is not good because this material shrink a lot whenpolymerize, high rate of CTE, so contraction and expansion is in high rate andthe bonding is not good.

Second generation (late 60s early 70s): similar concept to first

generation agents low success rate. Attempts were made to deal withthe smear layer

Third generation agents: same as the previous generation, howeverattempts were made to modify or remove the smear layer.

The smear layer is a layer ofmicrocrystalline and organic particledebris that is found spread on root canal walls and the cavity surfacesafter root canal instrumentation or cavity preparation. It is weakly

bonded to dentine and if we use acid etching properly will be removed.Consist of:

Dentine particles. Bacteria. Salivary constituents.

We said the hybrid layer is good layer, it's made from bonding agent that attach

to enamel and dentine and composite together, another layer is smear layer, itcan flow up dentinal tubule and prevent good bonding, so smear layer is not

good and hybrid layer is good, that's why when place the phosphoric acid, it isattendance to remove smear layer, open up dentinal tubule and clean thesurface, so we want to clear smear layer.

Before, they did not try to remove smear layer so the bonding was not good,now in second generation bonding agent they attempt to deal with smear layerand try to remove it.

Procedure in 3rdgeneration, similar to previous generation, but tries toremove smear layer and modify it.

Application of dentine conditioner (HEMA, or 2% nitric acid, ormaleic acid)

Application of primer (dentine bonding agent based on MRX), theprimer like a bridge bond to tooth structure and to bonding agent.

Application of adhesive (unfilled resin) Placement of resin composite
http://en.wikipedia.org/wiki/Microcrystallinehttp://en.wikipedia.org/wiki/Root_canalhttp://en.wikipedia.org/wiki/Root_canalhttp://en.wikipedia.org/wiki/Microcrystalline


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So firstly generations were similar, bonding agent was not good enough, andthey started improving the bonding between enamel and dentine and composite

during fourth generation.

Fourth generation procedure

Total etch technique for enamel and dentine. Rinsing with waterfollows, then gentle drying without desiccating dentine toprevent collapse 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 ensure drying of toothsurface).

Apply adhesive (bonding resin) then cure. Composite applied and cured.

As you see here we have extra step which is the primer, by this will make longer

time to work, more chance for errors to occur and more chance forcontamination.During fourth generation we start using what we talk about it last time the total

etch technique for enamel and dentine, in previous application, they only want tomake etching for enamel and this will not provide good bonding between a toothand composite.

Now they apply a material called the primer then followed by bonding agent andthen composite, now the primer is hydrophilic, it can be flow over a surface andin the same time it has hydrophobic end that capture a bonding agent, nowadayswe use only one bottle so we don't use a primer and bonding agent, the primeris added to bonding agent in one bottle.


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

Penetration into partially opened dentinal tubules. Formation of hybrid layer (hydrophilic monomer penetrate and

polymerize to form interpenetrating network with collagen

fibrils.

In fifth generation, fewer steps so better result because there is little chance oferrors. They used similar material as in fourth generation but the primer was

added to bonding agent in one bottle so they removed one step. So they tried topenetrate dentinal tubule, hybrid layer will be formed and potential wasimproving.

Fifth generation bonding agents: Etching is achieved using phosphoric acid. Priming and bonding is combined in one step.

Self etching primers, primer is added or incorporated with acid etching. 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.

Sometimes the primer is added or incorporated with acid etching, so it's anotherway for fewer steps, so again for fewer steps primer will be incorporated either

in adhesive or with phosphoric acid.

When the primer is added to acid and we applied it to the surface, there is noneed for rinsing, so this is for example one advantage of self etching primer sowe don't need for rinsing and drying, and there will be less dangerous of dryingor over drying the tubule.


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MicroleakageOccurs when the restoration does not completely seal the surrounding

margins of the cavity preparation. Because of polymerization, shrinkage ofthe composite make it a serious problem.

Possible outcomes of microleakage? Staining, sensitivity, andrecurrent.

What contributes to microleakage? If you don't cure bonding agentproperly, or don't provide isolation from contamination and saliva during

acid etching.

This picture about microleakage, They have the tooth, they present thecomposite properly in one side, and they also present composite to other side

but there was contamination, they contaminate the tooth during procedure andthen place it in solution contain dye to see if the dye can penetrate between the

tooth and filling. And then they look it under microscope, they noticed in sidethat there was no contamination the composite dens properly, there was no dyearound it, no microleakage, and where the filling was not made it properly for

example the composite not cure properly, there will be penetration of dye, canyou see the black area around composite, so there will be microleakage aroundfilling and you may see bacteria and saliva around it, It's very common to see ablack line around composite filling, and this represent staining due tomicroleakage.


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Factors that prevent good bonding

ZOE remnants factor, because of the eugenol prevent proper setting ofcomposite, if we have remnants from temporary filling, and we don't remove itor clean the surface properly, it will prevent good setting of composite and lead

to microleakage.

The most important factor is: moisture control Follow the instruction with regard to the time that should cure

both bonding agent and composite.

If we follow these steps with regard to acid etching, drying, bonding agentcuring, composite layering, incremental and curing, you will minimize the chanceof microleakage and minimize shrinkage.


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Measurements of bond strengthTests used:

Shear bond strength Tensile bond strength

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

Microtensile and microshear bond strength less variability. Eithershear strength or microshear strength or tensile strength is applied toknow the bond strength between composite or glass inomer cement andtooth surface.

Tensile strength is stress that stretches the material, shear mean sliding thematerial from each other.

So they use force to try and separate composite from tooth structure and tomeasure amount of force that need to separate them, the higher the force thebetter bonding strength.

Amalgam bonding

Older amalgam restorations leak less due to corrosion products. We tryto use a bonding agent between amalgam and tooth structure to minimizemicroleakage, but this way is not acceptable because it will not make different. Itis not commonly used because it will take a lot of time.

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 bondingPorcelain bonding and repair involves:

Sandblasting Special 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 applied Composite applied


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Crown and bridge which is made of porcelain, sometimes a small piece of it canbe fracture because it's brittle material, now when small piece of it fracture, you

don't have to replace the whole crown because it is very expensive, one way tosolve this problem is repairing it by composite and correct the defect.Underneath porcelain there is a metal, so if part of porcelain is broken, the metal

will be shown that's not esthetic, so to solve this problem you can usecomposite, so you need to use slightly different material, you need to etch themetal and remnants part of porcelain, but acid that we used here is different, it's

not phosphoric acid, in case of porcelain repair they used hydrofluoric acid.

Pit and fissure sealants 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 on top. Filled and unfilled resins, resin based pit and fissure sealant, it has

good strength and very successful, it's very strong material so it canhandle occlucal force.

GICSome of pit and fissure based on GIC, and some of them based on resin, similar

to composite resin but a little amount of filler in order to be able to flow.

PRR (preventive resin restoration) we need to use hand piece to open pit andfissure making very shallow cavity 1mm, then it filled with composite, on

composite we can applied pit and fissure sealant.If you think the pit and fissure is not cleaned, or might have caries, so you can

open it with hand piece, then filled with resin, and in the top we put the pit andfissure sealant, this procedure is called PRR.

Glass ionomer cements bonding1- Cavity preparation.2- Conditioner, made from polyacrylic acid.3- Rinse and dry.4- GIC is placed.5-Varnish on top of GIC.

D O N E B Y : E Y A D M A S S A L H A

bonding and adhesives (1)

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