What is C-Factor?

C-factor is more than the ratio of bonded to unbonded surfaces. Understanding C-factor, or Configuration Factor, is essential to understanding how composites behave in a tooth, but this topic was still being researched as manufacturers were trying to bond to dentin. Eventually, c-factor and its role in composite bonding showed the potential for a strong bond to dentin, but overcoming the c-factor stresses was the key element  that Dr. David Alleman studied in his search for predictable adhesive dentistry.

Articles referenced in this episode:

• Cho BH. Effect of interfacial bond quality on the direction of polymerization shrinkage flow in resin composite restorations. Oper. Dent. 2002;27:297-304.
• Alleman DS. The protocols of biomimetic restorative dentistry: 2002 to 2017. Inside Dent. 2017;June 64-73.
• Nakajima M. Bonding to caries-affected dentin using self-etching primers. Am. J. Dent. 1999;12(6)309-314
• Nikaido T. Evaluation of thermal cycling and mechanical loading on bond strength of self-etching primer system to dentin. Dent. Mater. 2002;18 269-275.
• Fusayama  T. Clinical guide for removing caries using a caries-detecting solution. Quintessence Int. 1988;19(6)397-401.
• Deliperi S. An alternative method to reduce polymerization shrinkage in direct posterior composite restorations. J. Am. Dent. Assoc. 2002;133 1387-1398.

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Transcript

0:33

In this episode will be reviewing six articles, foundational articles that talk about the direction of polymerization shrinkage that's called flow. The article that will be reviewing is by Cho and his group out of Seoul University, and the title is The effect of Interfacial bond quality on the direction of polymerization shrinkage flow in resin composite restorations published in operative Dentistry 22 Volume 27 Pages 290 72304. The second article will be the Protocols of Biomimetic Restorative Dentistry 2002 to 2017 by Alleman, Nejad and Alleman. This will give you the 18 protocols that are studied in a biomimetic approach. The third article will be by Dr. Nakajima and his group out of Tokyo Medical and Dental University

bonding to carious dentin: 1:32

bonding to caries affected dentin using self etching primers was published in 1999 in the American Journal of Dentistry, Volume 12, Page 309 to 314. The next article will be from TMDU again. This article one of the most important article that published information that impacts various detection, structural compromise, c factor and occlusion. The lessons one, two, four and six are impacted by this article. It's called Evaluation of Thermal Cycling and Mechanical Loading on the bond Strength of a Self etching Primer System to Dentin Lead Author T Nikaido. Dr. Tagami. Dr. Charlie Cox. This is just a superstar team from three different continents evaluating how bonding systems work when they're when they're stressed under occlusal forces and stress under C Factor forces. The fifth article will be from Dr. Fusayama, the father of International Adhesive Dentistry, published in 1988, in the journal Again Operative Dentistry, A Clinical Guide for Removing Carries Using Caries Detecting Solutions. Volume 19 of Quintessence International and the last paper, the classic paper on stress reduced direct composite technique, which is a part of every biometric restoration, whether it's direct, indirect or semi direct. We need to stress reduce the bio base. And this was published in 22 by Simone Deliperi and his mentor at Tufts University, Dave Bardwell. These six articles, if you master them, you will be well on your way to mastership of biomimetic restorative dentistry. Welcome, welcome. Welcome to episode three of Get Bonded Stay Bonded The Six Lessons Approach to Biometric Dentistry. In the first two episodes, we introduce you to some historical, important things. Today, we're going to get into the nitty gritty of what makes biomimetic dentistry there is in the world a big confusion about the difference between adhesive dentistry and biomimetic dentistry. We are going to clear that up today. Adhesive dentistry was the first approaches to bonding to dentin, and that comes from Japan. And that information coming to Japan is also in competition, with information coming from other manufacturers in the United States and in Europe. But those published studies about bonding to dentin were done in what is called a low c factor configuration. That is a very, very key concept. When I first was introduced to that in 1995, I had to read several papers to early understand it, and the papers, unfortunately are not easy to understand. So let me just show you what a paper like that would look like. You would be in a dental school library and you would see this or you would be in a dental library and you would see this. Now this looks like something is being tested and there's some apparatus that you've never seen before, and nobody's ever talked to you about it before. Because the papers that I started to read that I was introduced to by Ray Bertolotti or Gary Unterbrink in the mid 1995, they referred to C factor, but they didn't really explain in great detail what it is. When we talk about C factor, a textbook definition that you might get a test on in dental school would be the ratio of bonded to unbonded surfaces and you would get a passing mark on that. And quite often when I visited dental schools, as I referred to in a previous broadcast, I visited 36, 37 of the dental schools in the United States. To half of them. And I would always seek out seniors last year students, and I would ask them, What do you know about C factor in 35 out of the 36 schools? I got no satisfactory answer. Finally, I was at Tufts University Dental School and senior student I'm engaged with. And first we talk about carries detecting dye, and then we talk about bonding systems. Those are kind of the three lesson one Lesson three the things that would introduce you to adhesive dentistry. But the question, the c factor is lesson four. And that's the difference between understand adding adhesive dentistry and biometric dentistry. The student says. C factor is the ratio bonded and bonded surfaces. I was like, I've found Neo, you know, the one, the chosen one. And then I ask in the follow up question, what do you do to mitigate the effects of c factor? And he went back and he says, well I don't know, I'm going to be an oral surgeon. In other words, a dental student wanted to get an A he was taught c factor. He knows about restorative dentistry, but he still needed an A in that in that class in operative dentistry. So he memorized it. But he's going to be an oral surgeon. He's never going to use the concept of c factor in his professional career. that was a discouraging moment for me, because if the science is only used to pass the test and there's no practical application, what in the world is it even taught for? I always knew actually, I have to make a confession. Back in my earlier pre dental school days, I was thinking that I wanted to be an oral surgeon. I actually had that idea and I actually like surgery and I'm good at surgery. But if you're going to be an oral surgeon, you have to graduate in the top 10% of your class. During dental school, I had a large family and our third child had a major medical problem. There's no way that I could do all the things I needed to do to get a straight A's, so I had to decide I was going to be a dentist and that would be good enough. And I did. But the idea of fixing a tooth with traditional techniques, non adhesive techniques had nothing to do with this new technology that was introduced to me in 1995 by Ray Bertolotti coming from Japan. But then when the concept of CE Factor had an impact on the performance of the adhesives, then all of a sudden the adhesive is important and you can make an adhesive that from day one is terrible or you can make an adhesive from day one. Is mediocre or you can one that's better than average, or you can make one that is superior. And of course, this evaluation of the different bonding systems took basically 20 years to be established. This difference and the losers, the adhesive systems that were very bad and a low C factor configuration, they didn't get purchased and the ones that did well in a high C factor, they got better performance. But nobody ever told the dentist that was buying these materials that when they start talking about bond strength, it was just assumed that a higher bond strength was better. Usually that's correct. But nobody understood how high bonds strengths are actually maintained in the first 5 minutes or the first hour or the first two days of the performance of an adhesive system. And these are all considerations that have direct clinical impact. And so the idea of C factor impact in the strength of bonds was investigated first in these two papers that came out of Holland and the two papers that came out of Holland gave us a picture that was the Rosetta Stone of the invention of biomimetic dentistry. And this is the picture. So here you have a picture. This is enamel, this is dentin, this is recognized as a class five preparation. And here we have a composite that is shrinking and that's shrinking is creating stress or a pull on the bond to the dentin. And here at the bottom we had a black lines separating the bonded composite from the dentin. And the separation is right here. And this is a manifestation of c factor stress because the ratio of bonded to unbounded surface was very high above three. But my question was why did debond here and not here or here? Because the idea of stress being distributed equally in the polymerization of the mass, it obviously manifested in a separation, a gap in one area only. Wow. Now the people who make the biggest improvements in any science are the ones that ask obvious questions. Once I showed that picture to anybody, they will be asking that question. But now they have to get the answer. And the answer came with a new concept that I developed and that new concept is the hierarchy of bondability. Now, if you've read this paper that was published in 2017 by myself and Matt Nejad and Davey Alleman, then you'll be introduced to the concept of hierarchy bondability. And the idea is that the bondable surface that you're trying to bond to has the ability to be bonded quickly or slowly, depending on the concentration of the inorganic substance, which is hydroxyapatite That has some real practical applications because other papers that were going to be published in 2002, before this conclusion came, had some very important inclusions. And here's a paper that was published by a team from Korea. Dr. Cho. He investigated the effect of Interfacial bond quality to the direction of polymerization shrinkage flow. And Dr. Cho, when he said this in I read this in 2002, I thought, well, there's going to be some Korean doctor who's going to be teaching this sometime because he's right. He was studying the direction of the polymerization shrinkage flow. He used that word flow, and that's a precise term that came out of the previous studies in Holland. Flow is the movement of composite when they are polymerization. And that flow indicates where stresses can be weak or strong in a polymerization reaction in a adhesive restoration. Well, what that meant is that if we have this hierarchy of bondability to deal with what if we have a cavity preparation that has no hierarchy of bondability, This is my thought process. And the way to do that is to have a preparation that's completely enamel or completely dentin or in the more sophisticated analysis, intermediate dentin or deep. Then those are the four areas. And then there was a fifth area that is very common and that fifth area was identified in 1999 by Dr. Nakajima and published in a paper that when I read it changed everything. And it's probably one of the top ten most influential papers to the biomimetic approach of six lessons. And this is the paper. So this is the paper. So the paper is by Dr. Nakajima again out of Tokyo Medical and Dental. He had had his name on several of the early papers on bonding systems in their progress that were coming out of Japan. Nakajima Then he used the concept of caries detecting dye that Fusayama had said remove all sustainable dentin Fusayama made a mistake. It should have been removed darkly stained dentin. Nakajima, one of his students, knew that some of the dentin staining was much lighter than others, and that indicated a stronger presence of hydroxyapatite and less breakdown of collagen in which was actually the change in dentin that actually trapped the stains. And so Nakajima investigated what would we find in our bond strengths if we had this lightly stained? Then we knew that the strengths to the non staining dentin would be above 40 megapascals But he tested it and he found that the light pink staining was bonding at a little under 30 mega pascals. It lost maybe 25% of his bond ability or 40% in some areas. But this investigation in 1999 when it was published, I'm right in the middle of my literature review. I've been doing it for four years, 1995 to 1999 when this is published, and I read this in the American Journal of Dentistry. To me it's so huge because if we remove all of the pink staining, we are going to expose more pulps, not less. And that is what people who did not get trained by Fusayama like Nakajima, the people who just read Fusayama's papers and did what he said, all of a sudden they were exposing more pulps and having more pulps die. Well, the people in Japan and it had been using the caries detecting dye did not always remove all the stain in molars. It worked in anterior teeth, but it did not work in molar teeth with the four pulp horns on a molar particularly. But all of these ideas that you have Fusayama the Sensei teaching the next generation. The next generation has to decide how to interpret the master's words. And this was the first big break. And Nakajima and others, Tagami and Yoshiyama and Okayama University. Yoshiyama, a student of Nakajima, did further studies on bonding to carious dentin. And those studies now in my mind said, we have a fifth level of the hierarchy of bondability. We have enamel, we have superficial dentin we have intermediate dentin, we have deep dentin. If we bond all those together, we always know this is the bond that's going to be stretched and compromised. But now what if we have carious dentin the same thing. It's about the same as this intermediate deep dentin in hydroxyapatite. So it has the same bond strength of around 30 mega pascals. You won't get 40 or 50 like you would do enamel or to superficial dentin. But still this idea, when I added the fifth layer to the hierarchy of bondability, then I knew this had to be dealt with in a way that never stressed these layers or else you would have a decrease in bond strength. And the paper that was published three years after was again one of the most important papers that's ever been published. But again, if you publish a paper and nobody reads it, what is a result? Well, nothing changes. So here's the paper published in 2002 and their paper in 2002. The title is Evaluation of Thermal Cycling and Mechanical Loading on Bond Strength of a Self Etching Primer two System Cell Patch in Primer system to Dentin and Nikaido from TMDU, Charlie Cox from Alabama. At that time and to are three of the top authors. There's eight authors on this papers from three universities. But if you did not have the previous understanding of C factor and how that affected bond strength, you would not understand this paper because this paper dealt specifically with different C factors and different approaches to restoring a defect, and the defects that were restored could be restored either immediately with a direct composite or indirectly with a bonded onlay. But the bonded onlay was being bonded with immediate dentin sealing. And the conclusion of that paper and it was both in vitro without occlusal stresses and later with occlusal stress on their chewing machine. In Germany, Tunselmann’s chewing machine. It showed that if you did immediate dentin sealing and then bonded the onlay, then that high bond strength would be maintained under function. If you did a direct composite where the C factor stresses were generated in that early period of the restorations life, then you lost half of the bond strength in that early restorative period. And so let's say you started with in this and in this case we had bond strengths initially established in the high thirties and low forties with this bonding system that was being done in 2002, which is the liner bond 2V, if you now put that into a chewing machine, then the chewing machine could not fatigue the hybrid and there would be no decrease in bond strength. And that was with the immediate dentin sealing and an indirect restoration. But then if you had a high C factor restoration, which would be the direct restoration, then immediately you lost half of the bond strength. So it went from the low forties to the low twenties because of the C factors, stresses that were generated immediately. But then when they put those teeth into a chewing machine, an interesting phenomena was observed. It had another reduction of 10% of its bond strength. So all of a sudden they didn't maintain that 21, but they were fatigued to a 16. So you lost another 20% of the bond strength under function. Now the idea of an indirect restoration being better than a direct restoration, that's always been something that's been pretty much in a dental school curriculum. And so what the indirect crowns would always feel like they're superior to the large fillings. Well, this idea of is there something between a crown and a filling that adhesive dentistry now can achieve? And this paper said, absolutely. But again, you had to understand what C factor did immediately, which was reduce bond strength. And then if you have a compromised bond strength, these in other words, the hybrid layer has been stretched man under function, it starts to peel and eventually that becomes what we call a white amalgam, an unbounded white composite is no better and sometimes worse than an amalgam restoration that wasn't bonded at all. Although, I mean, this is, you know, I'm having thoughts of 20 years ago, but these 20 years of thoughts start to bring the idea that you need to understand these bonding systems in term of actual cavity shapes. And the actual cavity shapes can be dictated or can be modified with an indirect restoration or a direct restoration. But the real game changer came in the same year 2002, when I was sitting in my basement here where I'm giving this broadcast, and all of a sudden I read an article by some unknown dentist from Italy, and the unknown dentist from Italy is named Simone Della Perry, same year 2002, Simone de la Perry, Dave Bardwell. And all of a sudden there is somebody else in the world that's figured out what I figured out, and that is you overcome this hierarchy upon ability by using time to mature the bonds to these compromised demineralized areas, either in caries or deep dentin or deep on a root. There's also a lower mineralization and so Simone Deliperi, when he wrote this paper, he introduced a new way to restore the Tooth that was very innovative. And this picture here shows a peripheral shell is being constructed in a dentin replacement, and they're being constructed with increments that in this situation had 15 different increments to restore a tooth that most dentists would restore in one or two increments. Now, you know, when somebody is trying to introduce something new, it's not always correct. But Simone Deliperi, when I read this paper, I read first the references that he listed in the references, the real listed were 129 different 130 a missing one. It was actually 130 references. And then was I read those 130 references. I recognized most of those because they had been the same papers that I'd been studying now for seven years. And in seven years. You can't read all the literature at once, but you can read 130 articles in seven years and you can understand them because you'll have to read them more than one time like Simone did and like I did. But once you understand them and put them together, then you understand that stress relief to the hybrid layer comes by keeping all of the early layers to the initial, immediate and sealing. Then for a period of time, in some on paper, the absolute least amount of time that you had to stay very thin was 3 minutes. My conclusion was 5 minutes, but his layers were a little thinner than my layers. So we were both correct. But the Alleman-Deliperi rule that was generated and then later when we met in 2008, six years later, face to face and decided to teach together for ten years, then we started to teach the Alleman-Deliperi rule, which eliminates the problem of see that factor by staying thinner than two millimeters in the first 5 minutes after the polymerization of your dental bonding system. And that's as good as it gets. So we're going to finish this third episode, next episode, we will talk about some more important science that validated and confirmed. And now, 20 years later, in 2000, what are we, 2023? So we're 21 years later after all of these 22 papers gave us the concepts to overcome the c factor stressors. We'll talk about next week's topic decoupling with time. Until then, get bonded. Stay bonded. Always great talking to you.