Dental Concepts that Shaped a New Adhesive Dentistry: Biomimetic Dentistry

With the invention of new materials for restorative dentistry, new techniques for application were needed. Research in bonding to dentin showed bond strengths that approached the cohesive strength of a tooth, but getting this research into the hands of practicing dentists was another process entirely. 

As Dr. David Alleman was learning and researching new protocols in adhesive dentistry, his questions about why debonds occurred in select areas of the tooth led to his formulation of the concepts of the hierarchy of bondability and decoupling with time, all while creating his Six Lessons Approach to Biomimetic Restorative Dentistry. These new concepts that built on a foundation of dental research from the past four decades gave dentists anywhere the ability to bond predictably to deep dentin and restore the tooth in a way that mimicked the form and function of a natural tooth: biomimetic dentistry. 

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Transcript

0:40

Welcome to season three, episode 12 of the Six Lessons podcast. I'm your host, doctor David Alleman today we would like to talk about new concepts. What is a new concept? Well, it's something that you didn't know before. New concepts may be new to you and old to someone else, but if it's new to you, then it's exciting. If it helps, your life as a restorative dentist be better. What could be better than learning new concepts? There was a paper written 25 years ago by the team out of Tokyo Medical and Dental University, and, it said that because adhesive bonds, shrinks have been tested consistently at around 40 mega pascals, that we have something that's close to the cohesive strength of the natural tooth. Therefore, new concepts should be established. When I read that in 2000, I had already established several new concepts and no one else had ever thought about. Talk a little bit about that. And this episode, but what they were saying is that the old concepts were mechanically retained dentistry so mechanically retain crowns, mechanics retained fillings, required cutting of tooth structure so that you could make a shape that would hold in the filling, or a shape that could have a retention of a crown just with the friction of the surfaces that are touching each other. But adhesive dentistry now had the ability to have new principles, because we didn't have to have retention forms and resistance forms. Now, in 2000, there was actually a concept that I developed that went beyond what the Japanese had, and that was the hierarchy of bond ability. Now, the new concept of the hierarchy bond ability came to me as I was studying literature published in the 80s. In the 90s, and the literature from the 80s and 90s centered around a research team at Amsterdam University led by a physicist named Carel Davidson. And Carel Davidson trained in physics and engineering in England, went to Holland and stayed in Amsterdam, and trained dentists in the dental school on some of the concepts that physics and engineering teaches and uses every day to build bridges, to build roads, to build airplanes, to build cars. A very practical application of science. And the dentist, who were trained under Carel Davidson, had to again create new concepts. And as I read their papers, they were usually very short papers for pages, but very dense in their data collection and very innovative in the machines that they had to create to test these concepts. Now, if you're going to have a machine and you learn how to use it, that's one thing. The most common machine used in in basic, in vitro testing is called an instrument machine, which is able to create forces and test materials for their strength and their modulus of elasticity. And that's also used in testing bond strength. But it had the disadvantage of it was having a tensile force applied to these materials or a compressive force, but never a tensile force that would test the interface. So they had to create a device that would actually be able to pull composite that was bonded to dentin And then the dentin down here and the composite up here had this interface that was bonded with the bonding systems. And when they pulled, they were able to see when it gave way what the strength was. And this is measured in the engineering designation of Mega pascals named after Blaise Pascal, a great mathematician But Blaise Pascal, as a mathematician, was disciplined in his, ability to think about things and numbers, particularly, and he was, a father of both mathematics and engineering concepts. when the team out of Amsterdam measured the strength they had, also the, Disadvantage of being in this measuring of the strings during a large transition in the number of bonding systems and the different composite bits that were bonded to the bonding systems are bonded to dentin This transition happened in the mid 80s. It went from a chemical cure approach, which was the force first composites that were made, with what's called bowen’s resin, from three GM and the first dentist that ever got a batch of bowens resin that was a tooth colored material, was Paul Belvedere and this, this material, he had, in his office, of course, no FDA approval. It was totally, done the way the old science was done on your own dime. But Paul Belvedere was able to see how these light year materials were different than the chemical cure materials. And the chemical cure materials were based on an epoxy formula. And the epoxy resins were invented in 1936 by Kasten. And the epoxies always had an initiator that was camphor quinone and peroxide. It was a slow initiation of free radicals. It took about five minutes to get a real, what we call a gel point, where the materials would get hard. So they start out with two pastes. You mix the paste together, the chemical reaction for the initiation from the cancer quinone and the peroxide starts to polymerization of these methacrylate monomers. And then that was, making these dental restorative materials in the 50s when it first came out. Now those kind of reactions were known actually. Prior to that, in the, in the production of denture bases and the denture base evolution over 100 years, it went from a rubber base to a plastic base. And and so that was also something in the 30s and 40s that was coming into dentistry, but in removable frosted denture creations. Anyway, all these, transitions, they had to figure out why when they measured this stresses was accumulating in the composite that was bonded to the dentin. Why it wasn't greater because they calculated mathematically what the shrinkage should be and the shrinkage calculations, they came true, but they were measured after these composites had already polymerized. And this is the thing that they had to deal with that if you have a polymerize material versus an polymerized material and you measure the shrinkage, then you have to say, why is there more shrinkage on these materials that were testing. And the reason why is because the polymerize materials that they tested had already polymerize. And that had gone through the reaction, which is time based. It's a function of time. When you learned organic chemistry and in organic chemistry, every reaction has a beginning and an end. And so those rates of reaction are very important in different types of chemical reactions. They've been studied and many Nobel Prizes have been given on those types of, determinations. Of course, all these determinations are less than the human eye can see. And so the the shrinkage, percentage wise has to be appreciated with very careful measurements. And that's what physics is. And engineers are very, very good at measuring things on a very, very small scale. And so the new concept that came out of Amsterdam, was called flow. And so what they said is that when they mixed up these chemical cure materials and had it in a little mold here and it finally it polymerize, it shrank back. But there was a time about five minutes, that there was no stress that was measured on this machine that is attached to the end strong machine that measures the pull of these two components that were attached to the composite and the tooth. And so this idea of flow was instituting meaning. This was the theory. The molecules are developed in. And as they're developing they don't cross link immediately. They have linkages. And these long chains that we call oligomers or small polymers and eventually large polymers. But the large polymers start crosslinking these oligomers and small polymers. So all of a sudden they said, well, we've got this bonded surface here and some of the polymers are going towards that dentin bonding system that they had. But other the monomers are becoming oligomers independent of any connection. And so the mass of composite is polymerized in on top in this mold that is not bonded to the composite. They start having centers of polymerization attraction. And they start competing with the polymerization attraction or the polymers, the oligomers that are going towards the dentin bonded surface. These up here are independent for about three minutes because the monomers are moving in two different direction, the ligaments are moving in two different directions. The small polymers are moving in two different directions. And so these collections of molecules are moving past each other without being inhibited by a cross linkage, which would call cause a tension between the direction. Of the movement, which is called the dynamic movement or the polymerization dynamics. that flow that they said was the reason why more stress wasn't happening earlier in these reactions, that they're measuring. they estimated that in a chemical cure, you had maybe 90% of the stress reduction during that first three, five minutes. Wow. That's good. Stress reduction means that the hybrid is going to be developing during that time. Strengthened during that time in these experiments, they did not say what the time difference between the application to the surface of the chemical cure dental bonding system. They didn't say when they put it on, how long they let it sit. They just said that they put the dental bonding system on the dentin and then they mixed up the composite and then put it in the mold that was going to be touching and connecting to the dental and bonding system. That takes some time to do that, particularly the machine they had to hold with, some cellophane or plastic. Sides to, to do that. And when you read that, you know, I have all kinds of questions. Tell me exactly how long it took to mix the composite, to tell me exactly how long it took to place the composite into the mold. Tell me exactly how long it took to make sure you didn't have too much or too little composite. They didn't talk about that. But I was thinking that because I knew from my chemical background as a minor in chemistry, major in microbiology, that time was an element that always had to be considered in any organic chemistry reaction. Anyway, what they found out is that if they had a chemical cure composite in an unbounded mold, that they would have high bond strengths. Because this flow allowed all of the molecules to move in one direction, because it wasn't bonded to the mold, it was only mechanically held. But the mechanical holding is so huge compared to the chemical reactions it's having inside of this mechanical mold that you had all this flow moving in multiple directions, but basically finally in one direction, because there was no bond to the metal mold that was holding the chemical to or composite. When I finally understood what was happening there, I gave this a new name. I called this one Dimensional Flow. So one dimensional flow means you don't have any competing bonded areas, and all of a sudden you can get high bond strength because basically all of the polymerization first in the oligomers formation and then finally in the polymer small polymer cross linkage. Eventually they all went in one direction. So there was no stress on the hybird layer. Now, three years later. When now the like you're all the rage. The 84 1984 test that had the flow concept, that new concept when it tried to do a experiment in a cavity that they were able to make on an extracted tooth that had 4 or 5 sides, a deep class five preparation, basically on a bovine tooth. Then they put the bond on, and then they bulk filled the composite. They didn't have a way that that time to make that into their mold, because the composite mold wasn't filling a cavity, it was just being held on top of the bond to then. But once I got a class five cavity and then they had this reaction go through, they finally, at a certain period of time saw a separation at the bottom of the preparation. And so that was the deduction that they lost the bond strength there. And so the bond strength that they were able to measure on the instruction machine, they weren't able to measure on a cavity because they didn't have the way to hold on to the composite. Hold on to the tooth, and then test that, that test that was needed to understand what the bond strengths were inside an actual cavity that was shaped like a normal, dental cavity. That test wasn't developed until ten years later in 1994 by Hidehiko Sano So the new concepts testing had to be parallel with new materials and devices and techniques for the tests. And that's an engineering challenge. That's a challenge for a dentist trained by engineers. And Sano did that. He had some input from Nakabayashi but once they had that test, which is called the micro tensile test, they were able to test bottoms of cavities, sides of cavities. Obviously, flat surfaces were easy to do, like that initial instrument tests from Carel Davidson's group in Amsterdam. But the concept that I developed came from a question. My question is 1984. This competition between the bond and the polymerization stress. There was framed so nicely by Davidson. My question is why does it always fail on the bottom and not on the sides? Well, knowing that molecules move and they move according to laws of chemistry and the laws of physics, if you're going to have something bonded, then you have to have a certain strength to resist the polymerization that was established in the 84. And this was the question, The separation of the bottom part of the preparation was, in my mind, able to be connected with the micro tad anatomy, which I had been studying from. Hubert Schroeder. So Hubert Schroeder, who was the is the ultimate dental anatomist that's ever written a book. Which is called oral structural biology. He made it clear that any idea of what dentin's made out of, which in all the books, like Nakabayashi and Pashley’s book, But the diagrams are unbelievably detailed as all Swiss, productions are. If you want a Swiss watch, you have to have small details. Very well understood and drawn, but Schroeder made it clear that deep dentin is very different than superficial did. So instead of just saying dentin is dentin, he said there's basically four types of then you've got superficial, then intermediate dentin, deep dentin around the pulp and then root dentin. And so how was he able to determine this by analysis of the actual chemical contents? Mostly collagen, mostly hydroxyapatite. But the percentage of collagen, the percent of hydroxyapatite changed in the different parts of the tooth. So the tooth became stiffer on the top, close to the enamel, and more flexible in the root were the stresses of chewing were being absorbed, and so this difference of enamel, which is also another topic very rarely talked about by dentists. I've only known one dentist who's used the word deca, sated. That was my second mentor, Gary Unterbrink. He taught me that Alan Boyd, a non dentist engineer in London, had made some remarkable discoveries about the, enamel characteristics. And then Schroeder wrote about how it was formed. And the perikymata that you learn about in dental school is actually a manifestation of the odontoblasts and the ameloblasts that are dancing in basically circles. So most dentists think that all the enamel rods are straight. It turns out that none of them are straight. They're all dancing around each cusp. Eventually get to a tip. And that's why sometimes you little defect. Because right at the end of the dance, the tooth erupts and then the ameloblasts. Or are dead at that time. But this miraculous formation of enamel when you start going to dentin is just as miraculous. All of a sudden, we have these, odontoblasts that start, in the center of the tooth, which Pascal Magne very nicely summarized that the DEJ is the center of the tooth is not the pulp. In other words, in the development of a tooth, neonatal development of a tooth, everything starts its mineralization at the DEJ And then these ameloblasts keep going, make enamel. odontoblasts have to go twice as far, making the dentin the maybe six millimeters instead of only 2 or 3mm. But the odontoblast as they are doing this have a characteristic of more mineralization. The further away you are from the cell body. And so the cell bodies are in the pulp, in a vital tooth at birth. And those cell bodies stay there unless they're disrupted and have to be replaced through some type of trauma or some type of, infection, like dental decay. But these odontoblasts, are very productive for their whole life of regenerating new cells. And they have a connection with the dentin for hydration, through, pulpal fluid that is allowed after the it's produced to, hydrate the, the dentin But if you have a general deduction like in patchouli not Kobashi that you've got in dentin 50% hydroxyapatite and you have 30% collagen and 20% water, you have to realize that the concentrations differ, whether it's one of these four types of dentin superficial, intermediate, deep or root. And then you have to understand that these failed bonds that were first, actually demonstrated by Martin Brannstrom in 1982, the Japanese were were claiming that you could bond to dentin They bonded only on flat surfaces. Martin Brannstrom put the bonds into cavities in animals and then examined the teeth and then he found out that the bonds next to the pulp were always failing of these early bonding systems from Japan. So Martin Brannstrom publishes his book. In 1982, Fusayama published his book in 1980. Brannstrom was able to prove Fusayama was wrong, Fusayama publishes a lot of papers. Before he wrote a book, Brannstrom published a lot of papers before he wrote a book. But 1980 bonding is introduced and is totally disproved in 1982 by the Swedish, expert. And so that's when the Dutch get in to play 1984 the Dutch are going, okay, you guys, Japanese don't have it. The Swedes don't have. And we're going to show you the way. We're going to get down to basic science, chemistry. But then the chemistry has to interact with the biology. And that's where Schroeder and Doctor Dave Alleman come with these questions. You know, it's like the old TV detective Columbo. You know, he kind of rubs his hat and his hair's a little messy in the hat. And he's like, ma’am it sounds good. I just have one more question. To my question was, why does the bond always fail next to the pulp? And then the other question, why does it always fail in the deepest part of a box on a root? And it's all related to the amount of hydroxyapatite. It's there. So the new concept of the hierarchy of bond ability just means a different parts of the dentin have different amounts of hydroxyapatite, and those control the rate of polymerization bond strings that are established in these four types of dentin The main paper, they gave a new data to these new concepts that I'd been using in my own mind, and started to teach in 2003. The best data came in research that happened in 2002, Just happened to have a few copies of Erie 2002. Wow. When I read this, it was like that made me feel pretty good because the tests had bond strings to dentin coming out of the micro tensile tests in 1994 1996 were very high to dentin, and that was confirmed. It has been confirmed particularly, but that dentin bond strength was done without this configuration of the cavity stress being calculated because your own flat surfaces, as soon as they started to have some tests, were developed at Okoyama University. By Erie, they were able to get some numbers off of bonds that were bonded to walls, and they could be bonds to enamel or dentin. And what Erie discovered is that the early bond strength. What he called immediate setting shrinkage and bond strength testing is that he focus on the first three minutes of bonds that were being developed to enamel, and the first three minutes of the bonds being developed. And then and he found out that in the first three minutes, the bond to enamel was twice as strong as the bond to then. But then there was a crossover right at three minutes. All of a sudden this difference was neutralized and the bond strings to a dentin enamel were the same. And then after that, bond strength to dentin continued to get stronger. And the very next year, 2003, Bart Van Meerbeek gave us the data on those curves of the rates of polymerization and the strength of the polymerization. But the idea that Erie who to me I only know through his published papers, two of them, 2002 2004, published some important data scientifically based, and nobody in the world, even knows it exists. I mean, that's a tragedy. If you have a scientific basis for your life on earth. But if you have faith in science, you have to have faith, actually knowledge of the incapacity human brain to remember stuff. That's why I writing is maybe the biggest breakthrough in the evolution of human progress ever. But the idea is that with the written science, we can say with absolute certainty, since the signs have been repeated, even it's been repeated and it's on laboratory if it comes out of Japan. So far I haven't seen any signs that I've seen this disputed. Now, I haven't studied all of the science of all the Japanese universities, but there are other places in the world where the science is pretty lax, and the controls are pretty much not in place in the way that we would like them to be. And I think in a, probably last episode, I mentioned that Tokyo Medical and Dental University, Medical College of Georgia, Amsterdam University, Catholic University, Leuven, Belgium. if there's only four databases that you want to depend on, you go to TMDU KUL Amsterdam's research and then, University of Georgia medical College with Dave Pashley. So Takao Fusayama Dave Pashley, Bart van Meerbeek, Carel Davidson, those are the names that any scientist in restorative dentistry, adhesive dentistry that's evolved to biomimetic has to know them their research vetted over 40 years, 30 years, 20 years now becomes the scientific foundation for anybody trying to do something in restorative dentistry based on adhesive dentistry, not on mechanically retained dentistry. you know, the solution that I had, the hierarchy ability problem was decoupling with time. Many papers have tested that and proved it. There's many papers, but I'd say if one paper proved it more than any, you would have to go to Nikolaenko with, Roland, Frankenerger's direction. In Germany, the paper was published in 2004. So these papers that are published 2002 2003, 2004, the confirmation of these new concepts that I put into print hierarchy of bondability decoupling with time. These are my two of my great contributions to restorative dentistry and of course, Ribbond placement. Dissecting cracks into dentin. You know, these are another two. Those are maybe the top four contributions. But the six lessons in the hierarchy of importance gives us a framework to say, what's the most important thing. Well, you know, this is the last, episode of season three. So until season four, remember, get bonded, stay bonded. Thanks for listening.