 Hello everyone, welcome back to another session in dentistry and more Topic for today is dentine bonding agent on an undergraduate level. It is a confusing topic There's got around seven generations of bonding agents Some has a combination of etchant and primer some has a single bottle which consists of all the three components so all those are very confusing and the bonding with respect to dentine and enamel It differs. So there are techniques which is known as total etching and selective etching So I'll try to make it a simpler one So dentine bonding agent as we all know it is used in composites. So composites are preferred or amalgam in recent dentistry because of its properties the first thing is aesthetics it has got very good aesthetics and and comparatively strong Now we have so many Materials that is composite materials, which is as strong as amalgam and there is no mercury. That is the toxicity level is almost Minimal or zero we can say and it has got very good finish. So all these properties may composite very Patient-friendly and patient acceptance is very much is there mainly because of its aesthetics and would finish But what are the problems composite face? So composites though it has a chemical bonding with the two structure It is found that the failure rates are more than amalgam because of the bone failure or because of its low wear resistance and patients reports of post-operative sensitivity and Discoloration that is a marginal Discoloration mainly though it has some good properties. That is the chemical bonding its aesthetics and finishing the failure rate are More than amalgam. So the main problem is ultimately There is something known as Polymerization shrinkage So the material we use as a resin so resin is ultimately a Polymer so on Polymerization process the amount we use from the beginning and the amount we get as an output There is a difference that is the material shrinks so its size reduces So that causes the problem So there will be a gap between the restoration and the tooth because the material we apply in the beginning is not there at the end There is a polymerization shrinkage. So that problem is there. So many problems composites phase Ultimately the bonding system or the bonding mechanism should be perfect to have a longevity For the composites, so let's see what is a bonding system and what are the important factors which affects the bonding So as per definition bonding agents can be defined as Materials of law viscosity when applied on the tooth surface which forms thin layer or a thin film after sitting So this thin film strongly bonded to tooth surface on which the viscous composite Restorative resin is applied This sits forming an integrated resin So what are the ideal requirements of dentin bonding agent? So it should be biocompatible. It should not be toxic or irritant. It should have low film thickness and viscosity Then it should form permanent bond. It should have low thermal conductivity and good shelf life So basically we have three components in any system. The first one is itch and or Conditioner the second one is primer then the bonding agent or Adhesive so Dentin bonding agent has these three components So this is the actual agent these two we apply to get a good bonding with the tool structure But the problem with dentin is unlike enamel Dentin is a dynamic tissue Which is not having mineral content as much as enamel it shows changes due to aging, caries or restorative procedures and It has dentinol tubules which are filled with dentinol fluid which constantly flow outward from the pulp and As I said it has considerable amount of organic matter and water and it is close to the pulp So different chemical use for bonding or etching May irritate the pulp so We need to be very careful when we Do restorative procedures which is close to pulp that is in dentin So what are the common? etch and or conditioner or the primer and Adhesive or Sensor bonding agent. So the common etchants In organic acid section We have malic acid citric acid EDTA and tartaric acid And in polymeric acid we have polyacrylic acid then In organic acid section the most commonly used phosphoric acid and Nitric acid Whereas the primer we have ntg gma, pmdm, ppdm, Penta and Hema and The last one adhesives It is the most commonly used bis gma Udma in the diluent tech DMA and wetting agent Hema So the most challenging part in dentin bonding agent is to manage the layer which is known as Smear layer which is very commonly asked question. What is smear layer? So there is a presence of smear layer over dentin So the smear layer which can act as a hindrance to the bonding process So how does this form the smear layer is formed by the process of Cutting of tooth that is using a hand instrument or rotary instrument So it actually causes the small particles of the cut to surface to the tooth and it causes a layer which consists of microorganisms and organic content and water and this become a smear layer Which act as a barrier in the process of adhesion. Okay, so when we start applying composite It act as a barrier and there will not be any chemical locking between the or chemical bonding between the Resin and the tooth that is a hydroxyapatite So we need to remove the smear layer then only the proper bonding will happen. So the ultimate challenge of composite is to remove the smear layer So, how do we remove smear layer? So the smear layer it has got two phase that is a solid phase and There is a liquid phase. Okay So we need to remove the smear layer before that we need to learn something about this smear layer The solid phase which is made up of the cutting debris which is after this Tooth cutting process which consists of mainly the collagen that is denatured collagen and minerals and Whereas a liquid phase which is made up of the fluid fill channels around the cutting debris and there will be bacteria entrapped in the smear layer which can survive and Multiply beneath the restoration. So smear layer is a big challenge. We need to remove it So it can act as a barrier it lowers the dentine permeability It prevents a decrease in bond strength. It lowers the effect of pulpal pressure on bond strength So we need to understand the process of bonding We have tooth which is to get the bonding and ultimately the composite restoration In the beginning The tooth surface is normal. So we apply etchant. It is mostly phosphoric acid. So all happens is This is an acid Which can be a conditioner like 10 percentage Phosphoric acid it act as a conditioner that is a weak acid or it can be a 37 percentage phosphoric acid which is a strong acid which can Diminulize the tooth to a greater amount So anyway there will be a Micro porosities which is created on the surface of tooth and we are going to apply composite over here So this is going to be our composite. This is just a Representation not exact Tooth structure so tooth and composite So now we have everything ready that is the tooth with micro porosities which more surface energy and more surface area and Composite is ready to get attached to it. But the problem is The etchant is applied. Okay. So etchant is applied if we are applying 10 percentage of phosphoric acid that is a weak acid which is a weak acid What happens is sometimes the tooth Cavity will be in enamel and Dentane, okay, both places it will be there So this is a weak acid. Okay, so it cannot deminulize the portion of enamel But it can remove the smear layer. So this is basically known as conditioner dentine conditioner. Okay That is 10 percentage phosphoric acid But what happens if we apply 37 percentage phosphoric acid, which is a strong acid strong acid That causes deminulization of enamel, but it is almost Destroying the microstructure of dentine. So in both the cases The problem is there that is a composite will not bond to the tooth structure properly So in such case we need to use a different and the second problem is the dentine which is Hydrophilic that is which is having more water content and the composite resin is hydrophobic Okay, so this is hydrophilic and this is hydrophobic So getting a good bonding is very difficult. That is why we are applying a primer in between these two Suprimer is a resin, but it has low viscosity than the composite, but it can chemically bond with the composite Okay, so it is a material So we can say this is Primer Which has got two ends one and is hydrophilic Which will bond to dentine Okay And the second end is hydrophobic Which will bind to the composite So that is the function of primer which is a resin, but with low viscosity Because if it is not resin it cannot chemically want to composite because both are resins so it can chemically bond to this one So primer we apply in between The tooth and hydrophobic composite to make it happen. There is a bonding happen So dentine is hydrophilic. It has got lots of water content and this is hydrophobic and we apply primer And which which does the job of bonding? So the basic process is Etchant we apply first Then we apply primer then we apply bonding agent or Adhesive and over that we apply composite Okay, this is the process So while moving to the generations of bonding agent this three Process sometimes this will be combined sometimes this three will be combined Okay, so to make the dentist job easier So various generations are there. So that generations has improved the properties and Easier way to dispense a material. Sometimes we need to apply etchant first Then we need to wash it. We need to dry it. Then we apply the primer Then we cure it and we apply the bonding agent or adhesive Finally we apply the composite sometimes This two steps will be in a single bottle that is acidified primer So the primer is having the etchant within it So in that case what happens is we need to wait for a longer period because the etchant has to deminualize it Then the primer has to go in and create the bonding So we need to wait more time. Okay So in the beginning of this bonding agents first the concept was The total smear layer Removal so using a strong Acid the complete smear layer is removed. So even the smear plagues are removed smear plagues So smear plagues should not be removed. So once the total smear layer is removed the bonding has Substantially decreased because of the absence of smear plagues after that later it was believed that it is not the removal it is the Modification Modification of Smear layer completely. We are not removing the smear layer, but we are Modifying it leaving the smear plagues intact. So whenever we are applying Something on the dentine it should be a weak acid and on it Enamel it should be a strong acid. So that technique is known as selective etching Because first We apply the strong acid on the enamel so it will demonize it Then we apply the weak acid that is 10 percentage phosphoric acid on the dentine If it is just enamel, we just apply phosphoric acid. That is the process of etching. I'm talking about This process is known as selective etching. Okay, but the total etching process Total etching is there is no differentiation. We completely apply both enamel and dentine So that has this problem the first I talked about the problem the over etching will Collapse the in a dentine collage network and it will not properly demonize the Enamel because enamel has more mineral content. So this is the difference between selective etching and total etching So this is how it works. So there's three process that is a etchant. So after etchant it will be rinsing the micro power city is created then we apply primer which is a By and that is hydrophobic and hydrophilic ends Hydrophilic will join to the dentine and other one will composite because of this dentine and composite opposite Category hydrophilic and hydrophobic and all that we apply bonding agent. Okay, so this is the concept so we learned about what is smear layer how this process is happening and The selective edge and total edge concept So now we need to learn about the hybrid layer. So what is exactly hybrid layer? So hybrid layer so first We have etchant which created micro porosity suppose This is a truth. We are applying material here. This is dentine Okay, so we apply material So first we apply etchant. So etchant will create micro porosities After that we apply primer So primer will create a bonding between the truth and the upcoming bonding agent Next we are going to apply our adersi resin or bonding agent. So this adersi resin or bonding agent. So I'll apply this black color only So adersi resin and bonding agent which is going to Get attached to the primer and also to the inter tubular dentine. Okay inter tubular dentine. So this is known as hybrid layer Okay, so that is the zone where the adersi resin of dentine bonding agent micro mechanically interlocks Within the inter tubular dentine. Okay, this is a tubule and this is the inter tubular dentine So this resin that is adersi resin or bonding agent causes micro mechanical Interlocking within the inter tubular dentine and surrounding collagen fibers So first the etchant removes the smear layer and exposes the collagen fibers It also removes the hydroxyapatite within the inter tubular dentine Then the primer we apply which penetrates into the collagen network Finally, we apply the adersi resin along the primer Which form resin micro tax within the inter tubular dentine. So At the outermost we are applying The bonding agent or adersi resin. So which comes through the primer And it enters to the inter tubular dentine and forms micro So the hybrid layer, which is also known as resin dentine inter Penetration, okay And also known as inter diffusion zone That is a hybrid layer. So hybrid layer and smear layer. They are very very important in Exam that is in dentine bonding agent chapter So how the smear layer forms and what are the roles and how we can manage it and what exactly is hybrid layer So hybrid layer is the layer which forms After the etchant and primer application and the adersi resin which cause micro mechanical Bonding with the inter tubular dentine. So it is crossing the primer and it is Locking with the inter tubular dentine which was exposed or which was demonized with the help of etchant So that is Hybrid layer. So when a bonding agent is applied part of it penetrates into the collagen network Known as inter tubular penetration So this is the inter tubular penetration and the rest of it penetrates into the rentinal tubules cause the intra tubular penetration Okay, so the intra tubular penetration or the formation of resin tacks up to a limited depth of 10 to 20 microns So that is The concept of dentine bonding agent next we will be seeing what are the generations of dentine bonding agent? So this is a concept. So we need to understand the process first etchant primer and adersi and the differences of dentine and enamel and what is the total etching and the selective etching and what is the smear layer and its role and its management and the hybrid layer Now let's learn about various dentine bonding agent generations. So we have generation 1 to generation 7 On an academic point of view, we need to learn seven generations of dentine bonding agent In current scenario The dentists are using One of these three that is fifth sixth or seventh generation these four are outdated But still we need to learn The first two seven generations then only we'll understand how much improved the bonding system has in present scenario So the first generation It was based on NPG GMA So which was a surface active core monomer Which was first commercially available as a dentine bonding agent. So theoretically This NPG GMA was supposed to chelate with calcium in dentine to form a water resistant chemical bond to dentine So it was the first attempt to Bond to dentine that is by the process chelation using that calcium ions of dentine But the bond strength was very low around two to three mega pascal And clinically this agent did not successfully bond composites into dentine Whereas the second generation Where it was introduced in 1970s and attempted to bond chemically to either the inorganic or organic components of dentine But they produced only very limited bond strength, but it was comparatively better than the first It has got 5 to 6 mega pascal materials Tried where the halogen phosphoric acid esters of bis GMA NPG GMA or phenyl P And the examples are clear fill bond system F Scotch bond and bond light Whereas the third generation which is a three step method where the etchin has come into action We have primer and bonding agent So this is the first Where it started dealing with the smear layer and dentine fluid So they tried to Modify the smear layer to improve its property or by removing the smear layer without disturbing the smear plugs Which actually occludes dentinal tubules So the idea was to avoid aggressive etching of dentine because it caused pulpal irritation So they basically used 2% nitric acid or 2% malic acid with HEMA Or 10% citric acid with 3% ferric chloride or 10% phosphoric acid So example again Scotch bond gluma CNB metra bond Now we Are into the fourth generation. It is developed in 1990s. So it has got multiple bonds bottles Again So first we'll start with the etching using a phosphoric acid then we'll rinse the tooth Then we start applying the Material adders-erosin So the etchin commonly used are phosphoric acid citric acid or oxalic acid And the primers are NTG GMA HEMA or GPDM or 4 meta and adhesives are bis GMA or TEG MA And solvent what they used is acetone ethanol or water So all bond 2 Panavia 21 are the examples of 4th generation Whereas in the 5th generation what happens is The primer and bonding agent are become in a single bottle Okay, this is a syringe where we apply etchant in a gel form And primer and bonding agent are in Single bottle and this technique is known as total etch because it etch both enamel and denting. There is no selective etching Total etch technique smear layer is remote But the problem with this technique This etch both enamel and denting The advantage of 5th generation is we don't need to apply the primer separate First we need to etch then rinse then we can directly apply it and cure it Then we go for the composite filling But the strength of 5th generation is inferior to the 4th generation. It is a bond strength Now we are into 6th generation 6th generation where the etching and primer Are into a single bottle that is a Ascetic primer there is no separate etching or rinsing so that um saves a dentist time A lot because we don't need to etch then rinse the tooth then wait for uh, then we need to Try the tooth then applying primer But the only thing is we need to Do this for a longer period because first we need to etch the tooth then the deminolization happens Then the primer should enter and cause the Mechanical or the chemical locking so Manipulation is easy it shows bond strength good bond strength to denting but to enamel it has less bond strength So solvent is water basically And acidic primer is methacrylate for sweets so 7th generation where the entire system or the etching primer and bonding agent are in a one single bottle So it is the easiest technique. We don't need to etch the tooth rinse the tooth dry the tooth then apply primer then uh, bonding agent. We just need to apply the one bottle solution that includes etchant primer and bonding agent So 6th and 7th generation where the smear layer is Modified in 5th generation that is a total etch technique where the smear layer is Removed here it is modified So that is the generations of denting bonding agent So that was all about denting bonding agent. So we discussed about smear layer hybrid layer and the mechanism And various generations And the total etch technique and the selective etch technique So that's all about denting bonding agent. The only confusing part of denting bonding agent is this generations Of denting bonding agent. I hope I made it very clear And the smear layer and hybrid layer and how the things are different in denting and enamel So I'll come up with a new topic in dentistry and more. Thank you