lecture 8, bonding and adhesives ii (script)

8/3/2019 Lecture 8, Bonding and Adhesives II (Script)

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Bonding agents

This lecture starts from slide 23

Slide 23

Now we continue with bonding agent, currently the bonding agentdevelop several times, each generation is better from previous one,the purpose of this development is to make steps that will be madeless, so the time and percentage of fault will be less.

So basically the idea of bonding agents is to use material that able tobond both to enamel and dentine and in the same time bond tocomposite resin that place on top.

Earlier bonding agents based on silane coupling agents , did youremember in composite we talked about something we called fillerand matrix together it's called silane coupling agents, it hashydrophilic end that capture the filler and hydrophobic end or arm thatcapture the resin matrix and we called it to the resin.

Same thing in composite applied to bonding agents, so we wantsomething to have an end or representation by (x) for example thatwill capture mineral content from hydroxyapatite and another end oranother type of molecule that hold on collagen or organic componentin dentine, so it can place both on enamel and dentine hold on tothem then composite can be added and it can be chemically added.

So this is basis of bonding agents it will bond to enamel, dentine, andthen composite on top.

Let's start with generations

Slide 24

The first generation is distributed in 1950,it's based as we said onsilane coupling agent, if you don't remember what is the silane

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coupling agent you should go back to composite resin lecture, it's theagent that hold filler and matrix together.

This generation is representation by M-R-X model.

M: methacrylate group (hydrophobic and can attach itself to collagenand organic material in dentine)

R:hydrocarbon group

X: glycerolphosphoric acid dimethacrylate (it holds hydroxyapatitewhich is hydrophilic)

So the first generation is not good because: this material shrink a lot when polymerize high rate of CTE (coefficient thermal expansion), so contraction

and expansion is in high rate and the bonding is not good andmicroleakage will be very common, it's not good choice.

Slide 25, 26

Second generation appear in (late 60s early 70s), again similar

concept to first generation, they try to deal with what we called smearlayer.

Now, we will introduced to hybrid layer, we said that hybrid layer isgood layer, it's made from bonding agent that attach to enamel anddentine and composite together, so hybrid layer is good properly,another layer is called smear layer, smear layer is a layer thatcontain degree from enamel, dentine, food remnants, bacteria, it canflow up bone and dentinal tubule and prevent good bonding, so smear

layer is not good and hybrid layer is good, that's why when place theacid (phosphoric acid), it is attendance to remove smear layer, openup dentinal tubule and clean the surface, so we want to clear smearlayer .Before, they did not try to remove smear layer so the bonding was notgood, Now in second generation bonding agent they attempt to deal

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with smear layer and try remove it, again same type of bonding agentto first generation, no improvement .

Third generation, again similar to previous generation, but try toremove smear layer and modify it.

So firstly generations were similar, bonding agent was not goodenough, they started improving the bonding between enamel anddentine and composite during fourth generation.

Now we said that smear layer is made of dentine particle or enamelparticle and after cavity preparation it made of bacteria and somecomponent of saliva.

Procedure in third generation agents:

During third generation, they try to modify the smear layer or removeit by adding conditioner or acid or what we called a primer, severaltype of acid can be used, the purpose of all this acid is to remove asmear layer and to make a surface open and clean, after removal asmear layer they applying bonding agent then resin composite.

So maybe this generation is better a little bit than first and secondgeneration because a smear layer was removed.

Slide 27

This is representation of smear layer, it composed of saliva andbacteria, and this is dentinal tubule, so we can see how the smearlayer flows on dentinal tubule and prevent any bonding agent orcomposite from going on, so the bond is not good between filling and

smooth surface.

So , first generation based on silane coupling agent , secondgeneration and third generation is the same, but the problem is thesmear layer, they try to remove it by several acid ,and now we aremoving to talk about fourth generation where we start usingphosphoric acid.

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Slide 28

During fourth generation we start using what we talk about it last timethe total etch technique forenamel and dentine, in previous

application, they only want to make etching for enamel and this willnot provide good bonding between a tooth and composite.

So now in fourth generation at that time, they said that they want to tryetching both enamel and dentine, dentine has mineral content thatcan etch and dentinal tubule that you can open it and the bonding

agent will go in (in beginning, they start to etch enamel only , but infourth generation they try to etch both enamel and dentine to showhow the bond strength is , and they found that when etching bothenamel and dentine the mineral in dentine will go out by acid andbonding agent will go in dentinal tubule , so the composite will be hold

better to tooth)..

So etching will be done both to enamel and dentine , and you shouldmake sure not to have over etched dentine , after etching it should berinse and the surface should lightly dried , you should not to havedehydrated surface , and if you think that you have over dried dentineyou can wet it by small piece of cotton before you applying bondingagent.

Now they apply a material called the primer then followed by bondingagent and then composite, now the primer is hydrophilic, it can beflow over a surface and in the same time it has hydrophobic end thatcapture a bonding agent, nowadays we use only one bottle so wedon't use a primer and bonding agent, the primer is added to bondingagent in one bottle.

So in the past (the way that did the fourth generation): we made etching

added primer

added bonding agent

and finally added compositeSo it was foursteps

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Nowadays we make etching and wash and dry

added bonding agent

and finally added compositeWhere does the primer go? It will be incorporate in bonding agent sotwo in one.So it will be three steps

When we reduced steps the time of work and percentage of fault willbe less.

As a summary, bonding agents pass in several development, in thefirst three generation they used component or material similar to

silane coupling agent so one was hydrophilic and one washydrophobic to hold to the tooth and composite, then in fourthgeneration they started using phosphoric acid to remove smear layerbetween the surface, followed by a little amount of primer which ishydrophilic because the tooth surface is hydrophilic, so we wantsomething that able to flow and catch the tooth surface and bondingagent together, after the primer there will be another liquid which is abonding agent then followed by composite, this is for four generation.

Slide 29

Now in fifth generation, fewer steps so better result because there islittle chance of error(as we said when we increase the number ofsteps the time of work increase so the chance of error andcontamination also increase), so what they did?

They used similar material but the primer was added to bonding agentin one bottle so they removed one step from whole procedure, so theytried to penetrate dentinal tubule, hybrid layer will be formed and

potential was improving.

Slide 30

This is (picture) the fifth generation material, this is a bonding agentthat will be used in the lab and in the clinic, it's from 3M American

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company and it's called single bond adhesive because we used onlyone bottle that contain both a primer and bonding agent , and thismean that this liquid has both a hydrophilic and hydrophobic property,hydrophilic it can wet the surface of the tooth, hydrophobic it will bondto composite layer that will be added ( so we have compound thatable the material to spread on the surface of the tooth because it ishydrophilic and also we have compound that can hold compositelayer that will be added )

Slide 31, 32

Sometimes the primer is added or incorporated with acid etching (withphosphoric acid), so it's another way for fewer steps, so again forfewer steps primer will be incorporated either in adhesive or with

phosphoric acid, commonly we use single bond adhesive where theprimer is added to bonding agent, so this is the fifth generation .

When the primer is added to acid and we applied it to the surface,there is no need for rinsing, so this is for example one advantage ofself-etching primer so we don't need for rinsing and drying, and therewill be less dangerous of drying or over drying the tubule.

So the primer and acid put together in one bottle, and in the same

time or after many seconds we added the bonded agent, or in othersystem we add the acid etch and wash and dry then we add thebonding agent , again fewer steps and less chance to error.

This is (picture in slide 32) just example of different color available inmarket either bonding agent with primer or acid etch with primer inone bottle.

Slide 33

So this is just example of etched enamel or pores in enamel wherethe bonding agent is able to applied and flow in these pores to providemicromechanical retention

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Slide 34

To make acid etch tooth we want to dry it to apply the bonding agenton all the surface of the cavity, then we may use light curing in it and it

will be set because it is light cure material, usually we make lightcuring for twenty seconds, then it will be hard and set and it will flow inpores and dentinal tubule and set.

Slide 35

Microleakage is common problem in composite because ofpolymerization shrinkage, now we said several outcomes ofmicroleakage (staining, sensitivity, and recurrent caries).

Now what will increase the chance of microleakage aroundcomposite? If you don't cure bonding agent properly, or don't provideisolation from contamination during acid etching, all of these factor willincrease the chance of microleakage, so the more adhere or followthe steps actually then better chance of good adhesion between thetooth surface and composite

Slide 36

This picture represent microleakage so what did they do?They have the tooth ,they present the composite properly in oneside ,and they also present composite to other side but there wascontamination , they contaminate the tooth during procedure and thenplace it in solution contain dye to see if the dye can penetratebetween the tooth and filling..

And then they look it under microscope, they noticed in side that therewas no contamination the composite dens properly, there was no dye

around it ,no microleakage, and where the filling was not made itproperly for example the composite not cure properly , there will bepenetration of dye, can you see the black area around composite, sothere will be microleakage around filling and you may see bacteriaand saliva around it, It's very common to see a black line aroundcomposite filling, and this represent staining due to microleakage.

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Slide 37

This is table in your book contains factors that prevent good bonding,we talk about some of them, we talk about some of them like

contamination with blood or saliva or oil, oil can expel from hand pieceonto tooth structure, it can prevent acid etching and bonding agentfrom contacting between enamel ad dentine, because it will formseparated layer.

Another factor is present of ZOE remnants, because we said thateugenol prevent proper setting of composite, so if we have remnantsfrom temporary filling, and we don't remove it or clean the surfaceproperly, it will prevent good setting of composite and lead tomicroleakage.

There have many example of thing that prevents good bondingbetween composite and tooth surface, so we should know them, wetalk about most of them in the lecture.

But the most important factor is:

moisture control Follow the instruction with regard to the time that should cure

both bonding agent and composite.

So if we follow these steps with regard to acid etching, drying,bonding agent curing, composite layering, incremental and curing,you will minimize the chance of microleakage and minimizeshrinkage.

Slide 38Now we said that there is many ways of testing bond strengthbetween material, you need to go back to shear strength mean andtensile strength mean.

We said that tensile strength is stress that stretch the material,shearmean sliding the material from each other.

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So they use director of force to try and separate composite fromenamel and dentine ,and to measure amount of force that need toseparate them, the higher the force the better bonding strength.Now when we need examine material regard bonding to the tooth,what we will do?we put material (filling) on tooth surface, then we applied force eithertensile or shear strength on it and try to separate the filling fromenamel and dentine, the higher force we need to separate them thehigher bonding strength (proportional relationship).

So either shear strength or microshear strength or tensile strength isapplied to know the bond strength between composite or glass inomercement and tooth surface.

Slide 39

We talk about amalgam bonding in amalgam lecture where we try touse a bonding agent and composite between amalgam and toothsurface to minimize microleakage, but we said that this way is notacceptable because it will not make different.

So they try to use bonding agent under amalgam to improve bondstrength between amalgam and tooth surface, but in research they

found that this way will not make different, and not increase bondstrength, so it is not commonly use because it will take a lot of time,so just use amalgam from normal use, because your amalgam now ifyou adapt well to cavity, it will shrink to very small amount and notcause to microleakage.

Slide 40

Last coupling pages of your the chapter talk about how we can usebonding agent and composite to correct practice of porcelain oncrown and bridge, the only that you should know not the procedure,

just you should know the material.

Now in case of crown and bridge which is made of porcelain (made ofceramic, it's esthetic and very strong material, it's the material that we

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use in making of crown), sometimes a small piece of it can be fracturebecause it's brittle material, now when small piece of it fracture, youdon't have to replace the whole crown again because it is veryexpensive, one way to solve this problem is repairing it by compositeand correct the defect.

So some patient have crown, the outer part of it is made fromporcelain that make it very good and esthetic, sometimes a smallpiece of it fracture because it is brittle, so we don't need to replace thewhole crown it will cost (150-200) JD that's very expensive, so wecan use composite to replace the fracture part .

So underneath porcelain there is a metal, so if part of porcelain isbroken, the metal will be shown that's not esthetic, so to solve this

problem you can use composite, so you need to use slightly differentmaterial, you need to etch the metal and remnants part of porcelain,but acid that we used here is different, it's not phosphoric acid(phosphoric acid use in enamel and dentine), in case of porcelainrepair they used hydrofluoric acid.

So I need you to know the acid that you we use in porcelain repairingor etching is hydrofluoric acid, then silane or bonding agent is applied,then composite is added, so similar step but slightly different material( the acid we used in etching ).

Slide 41

We talk about fissure and pit sealant when we talk about glass inomercement, we said that some of pit and fissure based on GIC, ad someof them based on resin, similar to composite resin but a little amountof filler, they don't have a lot of filler in order to be able to flow

So these material can be successful, it's used properly, they need it to

be able to flow and wet the surface properly, so there can flow over pitand fissure and close them up.

They have usually resin based pit and fissure sealant, it has goodstrength and very successful, it's very strong material so it can handleocclucal force.

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There also can be used in other procedure, one of them we called itPRR (preventive resin restoration), which mean we need to use yourhand piece to open pit and fissure (very shallow cavity 1mm), then itfilled with composite, on composite we can applied pit and fissuresealant.

So there will be very shallow cavity, if you think the pit and fissure isnot cleaned, or might have caries, so you can open it with hand piecepair, then filled with resin, and in the top we put the pit and fissuresealant , this procedure is called PRR .

So if we want to use fissure and sealant alone, no need for use handpiece pair, and fissure should be clean, no carious, no staining, soimmediately applied fissure and pit sealant.

So these two ways are different from each other, when we dont havecaries or staining we make acid etching then applied pit and fissuresealant immediately on surface, but in PRR we make shallow cavityby hand piece pair then we add resin and in the top we add pit andfissure sealant .

Slide 42

We talked about glass inomer cement bonding, we said that aftercavity preparation, you need to apply the conditioner, which is madefrom polyacrylic acid, so we apply it for few second, and then we rinseand dry and GIC is placed, on top of GIC we need to apply varnish orbonding agent to protect it from contamination or dehydration, and thebond is chemical between GIC and tooth surface.

THE END

Done by: Manar Malkawi

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lecture 8, bonding and adhesives ii (script)

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