Using Chemical-Cure Dentin Bonding Systems for Endodontically Treated Teeth

Popular during the early years of adhesive dentistry, chemical-cure dentin bonding systems have since become less common with the rise of light-curing, but they still serve a purpose when restoring the pulp chambers of endodontically treated teeth. In this episode Dr. David Alleman discusses the polymerization dynamics of chemical-cure and light-cure adhesives and how that impacts their effectiveness in different aspects of a successful adhesive restoration.

Article referenced in this episode:

• Toshifumi Kuroe, Kana Tachibana, Yukinori Tanino, Noriyuki Satoh, Noboru Ohata, Hidehiko Sano, Nobuo Inoue, Angelo A Caputo, Contraction stress of composite resin build-up procedures for pulpless molars. J Adhes Dent. 2003 Spring;5(1):71-7.
• S Deliperi, D Alleman, D Rudo. Stress-reduced Direct Composites for the Restoration of Structurally Compromised Teeth: Fiber Design According to the "Wallpapering". Oper Dent. 2017 May/Jun;42(3):233-243. doi: 10.2341/15-289-T. Technique

At 12:35 Dr. Alleman creates illustrations to demonstrate air inhibition. To view this video, watch the episode on YouTube https://youtu.be/Y1xHishKlOo or search for Six Lessons Approach Podcast.

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Transcript

0:33

Hi, it's David Alleman. In this episode, I draw a few diagrams of the oxygen inhibited layer to see the visual. Watch this episode on my YouTube channel. Search six Lessons Approach podcast or find the episode link in the show notes. Welcome to season three, episode seven of the Six Lessons podcast. Today we'll be talking about, an important evolution in adhesive dentistry. That happened in the mid 80s. That's before most of you were born. I understand that, but, remember that if you don't learn history, you're going to have some problems with this history in adhesive dentistry. I, who was a participant in. I had to figure these things out, because the best people who were doing the research, it was hard to get that research into practicing dentists, operatories But, once I understood that the research needed to be amplified, synthesized, interpreted, and I started to do that for myself, then this difference between the chemical cure materials that were what I had in dental school and the light cure materials, which started to come on the market when I was first in practice, become very important. But it became very confusing in the six lessons approach, we have a framework. And when I had that framework first introduced to me by my second mentor, Gary Unterbrink it helped to crystallize my thinking onto how to make adhesive dentistry the most effective in most situations. And that was the first paragraph of his paper that he wrote in 1999 with Bill Liebenberg. And it said, you can think of adhesive dentistry as an equation between bonds and stresses. If you have bonds that withstand stresses, then the adhesion will withstand any, invasion. It won't be open to invasion from bacteria or to fractures. Those are all concepts that, became clear in my mind as I developed the six lessons. But in the six lessons approach, we have three lessons that talk about increasing bond strength. Lesson one, three, and five. Then we have three lessons to talk about decreasing stresses, lessons two, four and six. In the six lessons approach we differentiate between vital teeth and non vital teeth. Because a non vital tooth now, because of its nature and lack of hydration, becomes 300% more brittle, becomes 300% more likely to have a catastrophic failure. And so root canal treatment has always been a major goal for prevention in the six lessons approach. In my own practice, almost all of my catastrophic failures, perhaps I could say all of my catastrophic failures. I have seen two catastrophic failures in my lifetime. On vital teeth. These are patients that have come into my practice, and a natural tooth without a restoration had fractured in half, and the fracture went into the pulp into the root. The tooth was lost. And I can remember those very clearly in 44 years. if a patient comes in and they're due to split in half, you know that that's, that's a tooth that's not going to survive. the catastrophic failures that I helped to create were always related to root canal treatments and full coverage crowns. And as I started to document them and then I started to understand adhesive dentistry is a possible remedy and or even a prevention of these cases. Then, it became very important that I mastered the science of these new materials and develop new techniques. And so the six lessons for vital Teeth. But after you get trained in the six lessons, we give another lesson that's called lesson seven. And that's on anatomically treated teeth. How to restore a tooth is highly, prone to fracture. But the fractures that are catastrophic are in the roots. Those cannot be, eliminated totally with the six lessons approach, but the fractures in the coronal portion of the tooth can be totally, eliminated. But that's when we start to use a chemical cure approach. And that was the original approach that I always used on in the directly treated molars, where we had a pulp chamber and then part of the two structure that the missing dentin a pulp chamber would be about five millimeters in depth. And then the dentin on top of the pulp chamber would usually be another 5mm or 6mm and then two millimeters of enamel. So an endodontically treated restoration if we want to create the replacement of the dentin, which we refer to as the bio base, we understood that if we went into the pulp chambers, we would seal the portion that is most at risk of reinfection, which is the roots, and that the dental literature from anatomic literature showed that most failures of endo was not from an inadequate endodontic treatment, but from a reinfection, from an inadequate sealing of the coronal portion of the tooth, and so the sealing of the pulp chamber became very important, but it was large. The dimensions were usually five by five by five millimeters. And then on top of that you may have four by 4x4, dentin replacements. And so a bulk fill strategy in those areas, particularly the pulp chamber, became a little more, easy to achieve in the pulp chamber. We weren't really worrying about getting 50 Mega Pascals bonds strength or even 30. We just wanted a sealing of the orifices of the root canals. And so that sealing if it was 15 mega pascals, 20 mega mega pascals, that's a seal that, will withstand as long as the overlying surrounding tooth structure is bonded in that biomimetic number, which a natural tooth is connected to itself at around 30 mega pascals. And so the idea of buildup for pulpless molars, a very important paper, was published in 2003 by an all star team from two continents. Three continents. Actually, we have researchers, from the United States. We a researcher from Japan, we had a researcher from Italy. But this research team compared, light cure materials versus chemical cure materials, and it was always shown that chemical cure materials were less stressful to a bond. But there was a downside. And that downside was that the bonds for a dual cure compatible dentin bonding system had an initiation of their free radicals that was slower and less, energetic and less effective. So the bond strengths of these dual cure bonding systems were always, not as strong as the light cure systems. we have two systems that we teach in six lessons approach for restoring endodontically treated teeth. One is a total light cure technique with Ribbond fiber, which is called the wallpapering technique. And the paper that Simone Deliperi and I, published in 2017, is kind of the landmark article for that. Others have, tested these things and there are other fibers, but the Ribbond fiber, is the foundation to stress relief of the most important seal, which is the dentin's seal. Inside the tooth. If you want to have fracture resistance, different composites have different fracture resistance. And Ribbond does increase the fracture resistance in certain parts of the restoration. And that was shown by Willem Fennis in 2004, 2005, 2006. But there was a combination of placing fiber onlaying cusps and different materials light cure or chemical cure that needed to be tested. And this, paper by Kuroe the main author, Angelo Caputo, is the director of the research out of UCLA. Hidehiko Sano from Hokkaido University is also, part of the, team that does the investigation and what it said, that chemical cure still creates stresses, but they're less stressful than light cure. Now, the six lessons approach we've talked about shows how the Alleman Deliperi evolution. They stress reduced direct composite, particularly with fiber is the solution. If you want to have a light cure approach. And again, the paper that was published in Operative Dentistry, There were actually three articles that led up to the 2017 publication. The first was, of course, Simone’s classic paper on the Stress Reduced Technique, published in 2002, in the Journal of American Dental Association. And we followed up in 2009 with an article in PPAD that showed a very nice, vital tooth that was restored directly with the stress reduced technique, and then the final, the, summa of the research incorporated the wallpapering technique with Ribbond And those are the three papers that we made, our definitive approach to, restoring non vital teeth. But this paper, when it talked about that you still have a stress reduce reduction in chemical cure that was recognized in Fusayama's two books in 1980 and 1993. And Fusayama never was reconciled to the ability of a light cure restorative technique to be as good as a chemical cure technique. So all of the chemical cure dental the thesis that Fusayama, promoted in his research with Kuraray they all had a chemical cure, approach. And those systems that were first brought out that were called Clearfil F1, Clearfil F2, and Clearfil F3 were all chemical cure dental bonding systems. The next evolution in 1984, six years after the first three Clearfil systems that were only chemical cure were on the market in 1984 a new because this mid 1980s is when the change in bonding systems from chemical cure to like your happened. So they answered this how are we going to deal with doctors who want to go with these faster like cure materials because they were sold as faster and Fukuyama knew that polymerization dynamics said that that was bad for the bond. And it was proven in 1984 that it was bad for the bond out of Carel Davidson's, research in Amsterdam. in 1984, this new bond, which is a total chemical cure, advance, was the first bonding system that had ten MDP as the polymerization monomer. the ten MDP monomer, it wasn't known how superior this monomer was until years later, with more research. But now ten MDP is known worldwide. And of course this is only 40 years later, but 40 years later, ten MDP still is the best monomer ever developed as soon as the patent expired, of course, ten MDP was used by many companies. But this idea of using a chemical cure still was Kuraray And Fusayama and TMDU’s was main approach and it worked great if you had all the walls of a tooth intact. When I recognized this limitation, through the research, it was very important because quite often you have fractures where the walls are missing, or you have a deep box where you have sub gingival missing to structure or a crack dissection that we were doing regularly. And, since the, 2000s often had deep boxes, you had to replace a wall. And how do you replace the wall with a chemical cure? You can, but you have to matrix it in a very sophisticated way, which obviously is a good idea, needs to be done. But all of these overlapping questions, when do you oddly, a thin cusp, do you use a chemically or light cure in 1989, already came up with the material? That was a dual bond dentinal bonding system, and that dual bond dentinal bonding system was called photo bond. it was the first bonding system that I learned about from my first mentor, Robert Bertolotti in 1995. There was a huge problem with photo bond. Because photo bond is a great system from bonding to enamel. It's a terrible bonding system for bonding to dentin. And the reason is, is called air inhibition. So let me I've got a few pieces of blank paper. Let's see if I can put my artistic skills. okay. So here we have dentin Okay. On the bottom. And now we're going to put a dentin bonding system on top of the dentin. so we have dentin. We have the dentin bonding system. So that's the DBS. And so as we place, the dentin bonding system here, we had a underneath this, surface was prepared. Now you would etch and that etching would be five microns. And that's going to be called the hybrid layer. Let's see if that shows up. Hybrid layer. So here you have etched dentin. And then you have the hybrid layer which is infiltrated with your priming molecules. And then on top of this you have an adhesive layer. And so you have priming at five micron. And then your adhesive layer has a thickness And so the thickness of the adhesive layer is the critical mistake that was made with the photo bond system. They made a layer that instead of being 40 to 80 microns, which all gold standards have 40 to 80. Microns. That's the symbol for micron. So you want to have 40 to 80 micron. Why is that critical. And the reason it's critical is because on a vital tooth the Denton is pumping up fluid from the pulp continually with every heartbeat. What does that do to this priming area. So this is etched dentin with the photo bond system. So that means you have five microns of collagen that gives no bond ability. You can't bond to collagen And that was a theory Nakabayashi that proved to be not true. But this area here this is called transmutation coming from the bottom. So transudation puts fluid into this primed, etched dentin So the area here is becoming diluted. The monomers are becoming diluted by pulp of fluid. But then on top of this this layer is polymerize. But a polymerized resin that's using camphor quinone for its initiator the camphor quinone is quenched by oxygen. So this layer. Of the dentinal bonding system right here. If this is too thin at ten microns, that means this whole layer of your adhesive that when you put the light on it, if this layer is only ten microns, the whole layer does not polymerize. So you're priming and you're bonding. But if this layer is too thin when you put the light on it, this does not polymerize because oxygen has quenched all of the camphor quinone molecules. And so the transudation keeps coming up into this area. And you have, just a gooey mess that doesn't polymerize. And the only time this ten microns will polymerize is when another layer, at least another 10 or 15 microns is placed, but usually it's a layer of restorative composite, which would be 500 microns of global or 2000 microns if you put two millimeters of a composite on top of it. But you have this trapped, unplymerized fluid filled, pulpal fluid filled layer that if you start building on this restoration and now that goes back into the pulp, it hurts. You can't bite on it. This is the experience that I had with Photo Bond. But there was a solution that Ray Bertolotti did introduce me to, and it was a little bit disingenuous because he had a company that made a flowable composite and that flowable composite, if it was placed immediately and polymerized, then you limited this transudation And the next layer of flowable now starts to polymerize. And when it polymerizes all of the polymerization goes in this direction. So this is called a diffusion polymerization. And now you're polymerize in this layer of oxygen inhibited monomers. And they start polymerization getting hard. And this shuts off the pulpal tubule transudation is coming up. But this diffusion polymerization like that is something that happens with light cure. But it has to have a flowable composite component. Now the problem that was a little bit this ingenious from the Danville products is that the flowable composite had been made and put into the original photo bond system. The system was actually had a name and it was called Liner Bond one, and now came to market United States in before I was, trained in 1995. But the original liner bond one system, it knew that this inhibition of this thin photo bond adhesive, was a problem. So the solution to the problem was to put this global composite, immediately after you had, place you dentin bonding system. But this had a major problem to this flowable composite. The first global composite ever made in the world was Radiolucent. every country has really smart people, smart chemists. But every time you try to do something, problems will come up. And they're unintended, but still problems come up. And what's the problem of having a half millimeter layer of radiolucent material? It's sealing the tooth but it looks like there's a gap. It looks like you don't have a bond. And so the diagnosis of a next, dentist for treatment might say there's a gap here. We have some recurrent decay here, and then they would remove that. I mean, all of these stories are like, trigger my, you know, my worst nightmares because I had to live through all these things and deal with them. But the other problem, these dentinal bonding systems, the original dentinal bonding systems of the Clearfield F1, F2 and the new bond system F3, they initiated the polymerization reaction with an initiator that is called peroxide. Quaternary amine reactions. And so the composites that almost everybody uses around the world, the polymerization are not light cured, but they are reactions that are initiated with these Ammonium quaternary ammonium and peroxide reactions. And so that starts to polymerization to get from a gooey substance to a hard substance. But those chemical reactions are very slow compared to the chemical reaction that is initiate when you use camphor quinone, which all of the light cure materials. This was the breakthrough you had. This quinone molecule is very unstable. When light hit it it would generate free radicals immediately. And so many free radicals would be generated that it would be fast. And so a normal chemical cure reaction would get hard at about 3 to 5 minutes. light cure reaction would get hard in five to 10s. Well, if you're American, faster is better, right? Blah blah blah. Unfortunately, it would break the bonds. And this was documented in, in, University of Amsterdam and the bonding systems that depend on chemical pure bonding systems that would be called dual cure bonding systems. They all peaked out at about 20 Mega Pascals. And the reason why is because he did not have this interaction of the molecules in the the mineralized dentin and so all of these reactions down here in this gooey, flexible mess, just took too long and so the pulp of fluid continued to contaminate and to make the hybrid layers, weaker. And so all of the chemical cure, dental bonding systems always lost about 30% of their bond strength. And so if you were trying to get a bond strength, the 30, maybe you get 20. If you're trying to get a bond streak of 15, maybe you get five. And in different, you know, what we call the hierarchy of bond abilities, different substances were were bonding to particularly decayed areas that you were bonding to try to, allow the pulp to heal and prevent exposure. These areas, did not have sufficient bond strength, particularly in these deep box areas where the root, dentin was, less mineralized. All of these became recipes for, for failures. And I had many failures using the early techniques that I was taught. And I'm sure my mentors were doing the best they could, but it wasn't good enough. And so when we talk about using a light cure versus a chemical cure in reconstructing, we treated teeth, there is a step that we have to engage because we have to make these, interactions with the different materials on top, compatible with the materials on the bottom. And so if we wanted to use for example, a light cure material on top of a chemical cure material, that works fine because the light cure material on top, very energetic, is diffusing these monomers that are polymerized that we call oligomers. They're diffusing oligomers into the oxygen inhibited layer of the chemical cure material. And so that chemical cure material does polymerize from the diffusion of the photo activation through camphor quinone on the overlying lighter material. The opposite doesn't work at all. Meaning if you had a light cure material on the bottom, let's say your dental bonding system is light cured. You still have air inhibition. And so that layer of uncured monomers has to be polymerized again through diffusion. Because we now have this layer, this polymerize with the layer, this oxy inhibited. That's just a gooey mess of really soft molecules. But it has to be polymerized from the top through the diffusion, because all of the polymerization from the initial, like your it's done. But if you put a chemical cure on top of the oxygen inhibited layer of light cure, there's no help from the bottom. And so we have to have, these slow polymerization molecules diffusing, and they only diffuse about half and polymerize about half of the, light cured oxygen inhibited layer. And so if you're going to put a chemical cure on top of a like your surface, you have to change this like your air inhibition layer into a dual cured layer. So that dual cured layer now is starting to polymerize from radicals that don't need light to initiate, because you're overlaying them with this mass of composite. The light can't get through it. And so you have to have coating this air inhibited layer, a chemical reaction that is going to happen in the dark. And that's what chemical cure initiation happens. You have all of the molecules in this layer now are chemically reacting. So you have a a peroxide amine reaction that now this is polymerized in this layer. And any diffusion that you get from the overlay in is amplified by this, polymerization of this new, layer that you, you have. So what does that mean? If you're going to start to treat a tooth and you make your initial bond to deaden with light the depth of the cavity in the shadowing the cavity might mean that there is, an attenuation or a decrease of your ability to get a high bond strength. And that's what we see. And so you would have a 30% reduction in your bond strength, let's say, if you tried to have a nine millimeter prep and you have your your light here, you might get a 30% reduction in the activation of the camphor quinones. So that's been documented. But that's about the same that you're going to get with the chemical cure reaction also. And so you're you're not going to be able to make either of these situations in the pulp chamber ideal. As far as a biomimetic number of 30 or greater. But all you need again in the pulp chamber is a seal. All the strength of the tooth is coming from surrounding to structure and overlaying to structure that we call the compression dome. So the side to side bonding is coming from the outside of the root and outside of the tooth, like in a natural tooth inside the pulp chamber. You just need a seal so you're not relying on functional strength. From this, connection or this polymerization inside the pulp chamber. I mean, you might have to listen to this a few times if you give us some feedback. know, we can, do another, broadcast on it. But again, these are things that are facts of chemical reactions, and the chemical reactions have to be considered their chemistry. And the chemistry, again, also relates to the time and the reason why the chemical cure materials are less stressful is because they have less cross-linking during that 3 to 5 minutes, and the 3 to 5 minutes is the ultimate slippery rule of waiting before you stress your hybrid layer to dentin with overlapping layers of composite. But the wallpapering technique, I believe, is the superior technique, because you can take any wall that's missing and create that quickly with low stress, because you're creating a wall that has a very low ratio of bonded, unbound surfaces. The key factor on a wall that's resting on a peripheral seal zone, two millimeters in the bottom, five millimeters on both sides. The ratio of bonded unbounded surfaces is always going to be less than one when you're building this. And so when somebody figured it out, I figured out it was about the same time about, 1998, 2000. Simone was at Tufts University, and I was just in my practice trying to figure out how to fix teeth without damaging them more the way that I had done the first 17 years of my of my, of my practice. Anyway. So, you know, we want to invite you to get trained in this science Kuroe and Nakajima and, Nikaido Sano AA Caputo. I don't think we've mentioned that name before. That's the name that should be mentioned. Doctor Caputo wrote a book in 1986, which again, was a very fundamental book. Out of print, of course, now, but, it gave some very important ideas about stress reduction using chemical cure. But the stress reduction versus by modifying the Prep, which is a key factor reduction that also needs to be considered. And all of these things come together in the six lessons approach. So we encourage you to get trained. And we have many trainers around the world that are teaching pretty much every month, someplace in the world of Six Lessons is being taught. So we, we invite you to get trained by us or some of our masters, some of our ambassadors that are trained around the world. Until next time, get bonded, stay bonded.