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Welcome to episode four of the Six Lessons Podcast.
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In this lesson, we'll be talking about how bonding to curious Denton and bonding to sound Denton and the dental bonding systems that have been developed were only part of the equation for understanding how important the techniques that are used in a biometric restoration have to be integrated with each other.
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In dental school in 1975 through 1980 78, we had adhesive dentistry bonding to enamel, and that's what we called adhesive dentistry.
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It made possible tooth colored fillings in the front, but bonding to deaden was not known or taught at all.
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By the year that I graduate in 1978, that was the year that the first bonding system, which is called Clear Field Fill F-1, was introduced to the market.
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So 1978 Clear field left one comes to the market and everybody is like, well, does that really work?
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So in this episode we have some exciting literature to review.
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The first one is 2021 Decoupling with Time with Altmann and five other authors published in Inside Dentistry.
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The next one will be to book references, but the books aren't available in print.
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But you might be able to get copies or out of print.
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This is the 1993 Fukuyama textbook called a simple pain free adhesive restorative System by minimal reduction and total etching.
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His first book was actually published in 1980.
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There's a copy of that that I made a and then we have Articles three out of ACTA University Amsterdam foundational articles in understanding composite polymerization dynamics.
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The first one is called relaxation and polymerization of contraction stress by flow, and that was published in 1984.
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In the journal Dental Research.
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Carole Davidson is the lead author.
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The second is set in stress in composite restoration resin in relation to configuration of the restoration.
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Lead author is Fels Felson.
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Again, the team from Davidson that Amsterdam that's published in 1987, again the Journal of Dental Research.
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The next again the team out of ACTA is giving us the competition between composite dentin bond strength and the polymerization contraction.
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Stress. That's in 1984.
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And this article compares light cure materials versus chemical cure materials as the beginning of that separation in the profession where chemical cure was the only composites that were available for a decade.
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And now we get into light, cure the go faster, but have more stress.
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Not exactly what you want.
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In 1990, the same team Darryl Davidson supervises PhD student Chantal Kim Schultz, and she shows that lining certain composite restorations decreases the C factor the stress that was first outlined in 1987.
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So three years later, the first idea of a resin coating becomes introduced in the literature and then the polymerization stresses in the reaction.
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And that reaction now gives us a graph that we use very strongly in the six lessons approach.
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And that graph says in the first 5 minutes of your polymerization, you've got the most stress.
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So you have to understand this graph and how that relates to what you're doing in fixing a tooth.
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And the last word we reference in this episode will be 24 nickel ankle.
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This article comes out of Germany under the direction of Roland Frank Hamburger, a top researcher in adhesive dentistry and has published 24 in the journal Dental Materials.
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All right.
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Can't wait to talk to these.
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Well, when I was introduced to adhesive dentistry, they came from Fujiyama.
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They came from Tokyo Medical and Dental University.
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On this cover of this book, I made a list of ten generations of bonding systems that the company Cholerae has produced over this period.
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And in 30 years, actually only 27 years.
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It took 27 years to get the ultimate bonding system that was the easiest to use.
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It had the best performance.
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And that bonding system first came to market in the United States in 2005.
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These are new places and new concepts that I had no introduction to in dental school.
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And so I had to figure out what is working and what wasn't working, how that related to the traditional dentistry that I knew that part of the dentistry that I did was called adhesive dentistry.
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But bonding to deaden was not known or taught at all.
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By the year that I graduate in 1978.
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All these things are very complicated chemistry.
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And Bart Van Meer Bik in 1993 wrote his dissertation comparing 20 of those bonding systems, the 20 bonding systems that he used in 1993.
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There's only two that are still produced in the world.
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So there was 10% of the body systems that had something that was good enough that doctors would keep trying and keep using and keep bonding.
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So from 1978 to 1998, 20 years before we got to the self etching solution to the problem of smear layer removal, which we called conditioning.
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And then once we had this self-editing system, we had the ability to understand that we had simplified but not oversimplified, this approach to bonding.
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If we oversimplify by the approach, the bonding, and take the bottle of primer, which is hydrophilic, likes water, and the bottle, he said, is hydrophobic.
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If you do those separately in your priming and then bonding, then the hybrid layer has certain characteristics of a gradient, and that gradient has certain flexibilities as a bottle where it's moist and wet.
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And then other characteristics as it gets towards the surface is going to be restored with the composite.
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So that gradient in this hybrid layer, which was named in 1982 but refined in 1993 by Van mere B when he called it inter diffusion area zones.
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So these inter diffusion area zones that then Meier be identified were called deep, intermediate and superficial.
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In this little logo on a cap, this would be the deep zone.
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This would be the intermediate, this would be the superficial.
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Now, we do have a fourth zone that we'll talk about in our next lecture that gives us the ability to have even a better hybrid layer by not D minerals in any of it.
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The mineral content is removed by this acid etching, which had been Fukuyama's initial innovation taking bone, of course, acid etching of enamel to create these micro grooves that could be bonded to very quickly.
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But Fukuyama, when he uses acid etching, had the unintended consequence, and he understood the consequence of removing too much of the hydroxy apatite that expressed moisture from the vital pulp into the bonding field.
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And that complicates the chemistry.
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So that confounding variable of moisture being introduced from the pulp was eliminated by not etching.
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The dentin and the self etching approach came from the introduction of this molecule tin MDP.
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So once we have a self etching approach and it starts to get tested, then we have the ability to compare tests from different parts of the world.
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The article that I published with five other authors Davey Solomon, Simone Della Perry or out of Herodias Leandro Martinez.
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Felipe Clemens.
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This article was published in 2021 called Decoupling with Time.
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We talk about those different approaches and we identify what is called the gold standard body systems in the world.
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Based on the research that started in 1993 and has continued to this day 30 years later by using a gold standard bonding system, whether you use a total air conditioning or air abrasion conditioning to remove the smear layer, which has always been the weak link of the early bonding systems in the late seventies and early nineties.
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Then we have the ability to say what are our bonds to a flat surface?
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And that last flat surface bonding had been the gold standard for testing.
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And so when we tested those, we had the ability to say on a flat surface we have this amount of bond strength.
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But how many surfaces in a dental restoration, a cavity are flat?
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Well, not many.
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And so starting in 1984.
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So that's four years after Fukuyama says we can bond to dentin, then investigation of bonding to deaden not only on a flat surface, but on a surface that had sides, a cavity preparation that is common in restorative dentistry that started to be experimented with.
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And the experimentations start in Amsterdam with Carol Davidson.
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So Carol Davidson, in 1984 starts the discussion with this paper.
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And this paper is called Relaxation of Polymers Asian contraction stress by flow in dental composites.
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So this is a new term introduced by a team of researchers from Amsterdam.
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Carol Davidson himself was not a dentist, he was a physicist.
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But physicists experimented with products with chemicals and polymerization shrinkage of composites.
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This was an expertise that he had, and he started to test the different composites He had to develop unique apparatuses to measure the stress of polymerization shrinkage.
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The first apparatus that he developed in this paper got to look like a dumbbell.
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So we usually call this a dumbbell apparatus.
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So this is the dumbbell apparatus.
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Now, this dumbbell apparatus has hollow areas inside the top and the bottom.
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And then a hollow area here, and this is filled with composite.
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And then we have ten kilometers on both sides that whereas the compass as it is shrinking, it's supposed to pull these two ends of the dumbbell together.
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Now, the inside of the dumbbells, metal, there's no air abrasion, there's no bonding to do this metal through silent ization techniques.
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It's just holding the composite.
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It's a chemical, pure composite.
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And when they shrink the composite in this dumbbell, it didn't contract as much as they thought it would be because the shrinkage we knew the percentage of the shrinkage of the composite is just on a table and it shrinks.
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You can measure the the volume of the shrinkage.
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But in this contraption device, something happened inside these composites that relieve the stress.
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Now, these early compounds, 1984 are chemical cure composite.
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It takes 5 minutes to get hard.
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That's very important to understand because this mechanical containment of the composite, there was shrinkage of the composite, but only at a certain stage did the composite start to shrink in a way that the tenths alarm emitters started to come closer to each other.
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And so that had to be described and that was described as a free flow condition.
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In other words, the molecules are composite, are coming towards each other.
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They're connected inside of this dumbbell, but they're not connected to the walls of the dumbbell.
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So there's no holding mix with the bond, the walls and all of the movement is the composite molecules moving towards each other.
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So that's called free flow condition.
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And if you have a free flow condition, then there was no stress on these two ends of the dumbbell.
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Whoa, That was something that needed to be known.
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So what they figured out is that if you were holding a mass of composite and you didn't get much stress, it was because these molecules were slipping by each other and are slipping by you know each other means that the cross-linking was at a minimum.
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Once they started cross-linking it about 3 minutes.
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Then they started to have some stress and then a minute for more stress.
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And the most stress was at minute five.
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And that's when the cross-linking was at a maximum.
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And that's called the post gel point of composite.
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It polymerization.
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This was interesting information.
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But then again, how does it apply to actual cavities?
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Well, the application to cavities was investigated three years later by the same group if we now have a constraint.
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So they made this machine, unlike the dumbbells, this had two flat plates and the food two flat plates now had columns of composite that were connected to the two flat plates.
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They were bonded to those flat plates.
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So there wasn't a a free flow, but they actually had in between these two flat plates, this composite was shrinking, but it was connected to both plates.
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And so what they found out is that in that situation where you are constrained on one side or on both sides in this situation, then the amount of composite that you had in between those two plates had a relationship on how fast and how strong the stress was going to be.
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In other words, the plates are like this.
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You got a composite column here.
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Once that chemical Kier Composites starts connecting in that 3 minutes, 4 minutes, 5 minutes, then these plates are moved towards each other.
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That sense by the ten kilometer on each side, and that starts pulling them towards each other.
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Okay.
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If they held the plates so they could not move, then the only thing that would happen is that the composite would have the movement of the composite molecules just like it was shown in the first experiment.
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And so if you had a large column of composite, there wasn't much stress.
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If you had a short column of composite, then the cross linking happened percentagewise much more rapid.
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And so that caused more stress.
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So they were able to calculate the surface area of the two round plates and the surface area of the unborn, a composite.
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And if they had a large surface area of onboard a composite, then there wasn't much stress on the plates.
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So the ratio of bonded to on bonded surfaces became the definition of see factor configuration factor.
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Every textbook talks about configuration factor every year, peculiar talks about because configuration factor.
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None of them have explained it to the way that they needed to explain it, because I actually read these articles in detail and I understood that, for example, if you have no bond to your apparatus or a cavity, then all the shrinkage moves in one direction.
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And so that's called free flow.
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In this experiment, it was not free flow because we had bonded surfaces here and bottom surfaces here, but the flow is happening in the unbounded composite.
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So there was things happening in the composite movement as the column was large compared to when it was thin.
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And we had a lot of cross linkage percentage wise happening earlier.
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What that meant is that if you eliminate the free flow, then you have to say, what kind of influence do you have on the bonded surfaces in this situation?
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Bonding to metal with the composite is very easy to do.
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There's no moisture, there's no collagen, there's none of the slippery or flexible characteristic.
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Six of of dentin.
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So these have 100% bond strength.
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And so we've eliminated the hybrid layer development.
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And as a confounding variable in these shrinking composites, the hierarchy of bond ability was a concept that I introduced to explain then why these experiments can't be directly used to understand how composites work in cavities.
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But the next published paper that was published again in 1984 had another device that they had to invent and this device is this little jig here.
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So we have a tense laminar on one end, tense laminar on the other end.
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We have dentin.
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This little triangle piece here is dentin.
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And then we have the the column of composite that's on top of it.
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Now, the top of it that holds the composite is being bonded to.
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Then again, this is a free flow.
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That is the core situation.
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There is no bonded surface to this metal.
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And so it's just bond.
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It's a deaden.
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And this free flow means that the unidirectional bond will move towards the dentin.
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And they were able to get bond strength at about 19 mega pascals in 1984.
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So here we have a free flow condition on top, but a constrained condition only on the bottom.
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That's different than the experiment that established the idea of C factor, where you have two constraints, then you have no difference in bond ability between different areas of the of the shrinking composite.
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But then when they took that idea and put it into a three dimensional cavity, they came up with this result.
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So here we had a now a three dimensional cavity that we had some constraint here.
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Constraint here, constraint here, meaning it was bonded to enamel, bonded to enamel here.
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But then as we got down here and we were bonding it to dentin, as they did the experiment, but they never had a lamination of the enamel on either side.
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They had very little d lamination in certain areas that were right next to the enamel.
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This is called superficial dentin, but the main gap that was formed was always in this deep area, which we called intermediate dentin or even deeper dentin, as it goes to 2 to 3 millimeters deeper past the DG.
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So this is what they showed.
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And then six years later, one of Kiel Davidson's graduate students, Chantelle Kemp's Shorty, did another experiment trying to solve that problem of how to prevent that D lamination in the bottom of the cavity.
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And they started to experiment with different liners.
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The only liners that had any success were composite liners.
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There was no flowable composite at that time.
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It wasn't invented yet, but they did have some less viscous liners that work, and those liners had the ability to have some sealability.
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That was published in 1990, another paper that's been forgotten.
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But when I read that paper at this time, I'm trying to think now these composites are basically the same as the liners.
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That doesn't make sense.
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In other words, you get a gap formed with the composite and you have something like the composite and you get less of a gap.
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What's the difference?
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And in my mind, you know, which is a little bit out of the box thinker, I'm trying to, you know, discover things that that I don't understand.
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It gave no mind that it took time to put these liners onto that floor and the composite liners that did the best.
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It took a little bit of time to adapt them.
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And I was enough of a chemist to know that every chemical reaction has a beginning, a middle and an end.
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And so I related, as I discovered this this paper was published in 1990.
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The other papers were 1984, 1987.
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I remember I didn't start investigating any of this until 1995, so I had to go back and find these papers.
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I had to get these papers from other references, from other articles.
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That was important, but not clear in the later articles that were published.
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Later articles would talk about C factor, later articles would refer to flow, but they didn't really start coming together until 1980.
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So in 1999, 2000, 2002 and in those years, then we started to have some real research that gave us the combinations of these approaches.
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And so the concept that came into my mind and it was stimulated more by Carel Davidson than any anyone else, because this idea of composite movement, when Cho investigated this and and published his research, there was also something that I learned in 2000 from my second mentor, Gary Unterbrink, who was speaking at a lecture set up by my first mentor, Ray Bertolotti This was in 2000 and I wrote this in my notes and it said, Composites move towards the best bonded surface.
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And so my first mentor, Ray Bertolotti introduced me to the concept of C factor.
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I did hear that first from him.
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Gary Unterbrink The idea of flow and of the composites.
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He was referring to that, but he was not understanding that how it directly related to an indirect restoration or a direct restoration.
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And so the time elements of how the composite flow moves early on is something that I had to figure out.
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And there were many papers being published and they would have graphs like this graph.
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You can see this has a beginning and end and this is the polymerization that's going like this.
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And the numbers that are down here at the bottom were significant because there was always in this first 3 minutes of very strong polymerization starting and the strong polymerization was much stronger with the Camphorquinone like cured composites that were now being investigated in the late eighties, early nineties and then into the nineties.
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The Light cure composites basically took the the field of dentistry by storm, created graphs like this was published this one was published in 2004 by him out of University of Colorado, Lou Stansbury and Bowman.
00:26:53.094 --> 00:27:07.008
And this is the graph and this I say has been shown over and over again if you have a light, your material, then you have a time of very rapid polymerization beginning and then it plateaus.
00:27:07.075 --> 00:27:09.777
The polymerization actually lasts.
00:27:09.777 --> 00:27:14.215
Molecules are still polymerization at 24 hours.
00:27:14.315 --> 00:27:20.688
A few molecules are reacting to these free-radical polymerization connections.
00:27:20.755 --> 00:27:34.135
But in a direct composite, you have about 60 to 65% of the monomers that are glamorized after 10 minutes and then the rest are polymerization and small amounts.
00:27:34.235 --> 00:27:43.111
But this early polymerization, what we call the beginning of the plateau, is always at 5 minutes.
00:27:43.211 --> 00:27:51.052
And so that led me to the conclusion that you have this five minute window where a lot of polymerization happening.
00:27:51.119 --> 00:27:58.493
The stress only comes from the polymerization and the polymerization has to be connected to walls.
00:27:58.593 --> 00:28:15.276
So we have some constriction when we have walls, but the polymerization of multiple walls only starts to effect the hybrid layers at that early five minute situation.
00:28:15.276 --> 00:28:22.917
So this is developing in my mind between the years 1998 and 2004, really.
00:28:23.017 --> 00:28:31.526
And in 2004, a landmark paper that was published, we call Nikolaenko 2004.
00:28:31.626 --> 00:28:37.498
And in that paper it gave us real numbers using gold standard bonding systems.
00:28:37.598 --> 00:28:45.373
On how C factor affects the bond strings of these restorations that are adhesive restorations.
00:28:45.373 --> 00:28:58.686
The title of this paper is The Influence of C Factor and Layering Technique on Micro Tensile Bond Strength two then 24 published in the journal Dental Materials.
00:28:58.753 --> 00:29:26.013
And what Nikolaenko found is that if you have a thin layer that's horizontally placed in the deep part of the cavity or you got a four by 4x4 cavity shape, if you do one millimeter and then the second millimeter and then the third millimeter, and then the fourth millimeter, the bond strength at the bottom of the preparation next to the pulp is doubled.
00:29:26.013 --> 00:29:33.855
If you bulk fill that 4x4 by four, then you lose 80% of your bond strength.
00:29:33.921 --> 00:29:53.942
And so the number that they came up with, with this one millimeter horizontal layering was 30 megapacals using a gold standard bond system like off the bond fell and that 30 megapascals all became very important because that is the cohesive strength of enamel.
00:29:54.041 --> 00:30:16.731
So if we can't connect these deepest parts of the tooth at the same strength that enamel is connected to each other, we call that mimicking the strength of a natural tooth or Biomimetics definition is connecting you to side to side, front the back and top the bottom around 30 Megapascals the same as cohesive strength of enamel.
00:30:16.798 --> 00:30:40.154
So with that then we had the time element and the thinness element of a layer confirming what was published two years before in the Deliperi Bardwell paper that gave us the idea of a stress relief by limiting the volume of the increments that are placed on top of the hybrid layer.
00:30:40.221 --> 00:30:44.992
So that's the end of this episode.
00:30:45.126 --> 00:30:50.898
We will continue talking a little bit more about this next time.
00:30:50.965 --> 00:30:52.300
Get bodied, stay bonded.
00:30:52.300 --> 00:30:53.467
Always great talking to you.
00:00:26.710 --> 00:00:31.881
Welcome to episode four of the Six Lessons Podcast.
00:00:31.981 --> 00:00:57.707
In this lesson, we'll be talking about how bonding to curious Denton and bonding to sound Denton and the dental bonding systems that have been developed were only part of the equation for understanding how important the techniques that are used in a biometric restoration have to be integrated with each other.
00:00:57.774 --> 00:01:08.951
In dental school in 1975 through 1980 78, we had adhesive dentistry bonding to enamel, and that's what we called adhesive dentistry.
00:01:08.951 --> 00:01:18.762
It made possible tooth colored fillings in the front, but bonding to deaden was not known or taught at all.
00:01:18.896 --> 00:01:31.307
By the year that I graduate in 1978, that was the year that the first bonding system, which is called Clear Field Fill F-1, was introduced to the market.
00:01:31.375 --> 00:01:47.391
So 1978 Clear field left one comes to the market and everybody is like, well, does that really work?
00:01:47.456 --> 00:01:52.028
So in this episode we have some exciting literature to review.
00:01:52.028 --> 00:02:02.906
The first one is 2021 Decoupling with Time with Altmann and five other authors published in Inside Dentistry.
00:02:03.006 --> 00:02:07.977
The next one will be to book references, but the books aren't available in print.
00:02:08.078 --> 00:02:12.115
But you might be able to get copies or out of print.
00:02:12.281 --> 00:02:24.828
This is the 1993 Fukuyama textbook called a simple pain free adhesive restorative System by minimal reduction and total etching.
00:02:24.995 --> 00:02:27.997
His first book was actually published in 1980.
00:02:28.231 --> 00:02:42.812
There's a copy of that that I made a and then we have Articles three out of ACTA University Amsterdam foundational articles in understanding composite polymerization dynamics.
00:02:42.812 --> 00:02:51.521
The first one is called relaxation and polymerization of contraction stress by flow, and that was published in 1984.
00:02:51.521 --> 00:02:53.456
In the journal Dental Research.
00:02:53.456 --> 00:02:57.961
Carole Davidson is the lead author.
00:02:58.060 --> 00:03:05.569
The second is set in stress in composite restoration resin in relation to configuration of the restoration.
00:03:05.569 --> 00:03:07.069
Lead author is Fels Felson.
00:03:07.069 --> 00:03:16.879
Again, the team from Davidson that Amsterdam that's published in 1987, again the Journal of Dental Research.
00:03:16.947 --> 00:03:26.757
The next again the team out of ACTA is giving us the competition between composite dentin bond strength and the polymerization contraction.
00:03:26.757 --> 00:03:29.759
Stress. That's in 1984.
00:03:29.860 --> 00:03:44.240
And this article compares light cure materials versus chemical cure materials as the beginning of that separation in the profession where chemical cure was the only composites that were available for a decade.
00:03:44.307 --> 00:03:49.946
And now we get into light, cure the go faster, but have more stress.
00:03:50.047 --> 00:03:52.315
Not exactly what you want.
00:03:52.315 --> 00:04:12.702
In 1990, the same team Darryl Davidson supervises PhD student Chantal Kim Schultz, and she shows that lining certain composite restorations decreases the C factor the stress that was first outlined in 1987.
00:04:12.702 --> 00:04:24.781
So three years later, the first idea of a resin coating becomes introduced in the literature and then the polymerization stresses in the reaction.
00:04:24.880 --> 00:04:32.988
And that reaction now gives us a graph that we use very strongly in the six lessons approach.
00:04:33.055 --> 00:04:39.663
And that graph says in the first 5 minutes of your polymerization, you've got the most stress.
00:04:39.862 --> 00:04:48.437
So you have to understand this graph and how that relates to what you're doing in fixing a tooth.
00:04:48.504 --> 00:04:55.879
And the last word we reference in this episode will be 24 nickel ankle.
00:04:55.946 --> 00:05:07.290
This article comes out of Germany under the direction of Roland Frank Hamburger, a top researcher in adhesive dentistry and has published 24 in the journal Dental Materials.
00:05:07.391 --> 00:05:08.692
All right.
00:05:08.692 --> 00:05:11.694
Can't wait to talk to these.
00:05:11.795 --> 00:05:17.000
Well, when I was introduced to adhesive dentistry, they came from Fujiyama.
00:05:17.100 --> 00:05:20.871
They came from Tokyo Medical and Dental University.
00:05:20.937 --> 00:05:32.182
On this cover of this book, I made a list of ten generations of bonding systems that the company Cholerae has produced over this period.
00:05:32.282 --> 00:05:35.485
And in 30 years, actually only 27 years.
00:05:35.585 --> 00:05:42.459
It took 27 years to get the ultimate bonding system that was the easiest to use.
00:05:42.459 --> 00:05:44.860
It had the best performance.
00:05:44.860 --> 00:05:52.436
And that bonding system first came to market in the United States in 2005.
00:05:52.536 --> 00:06:00.076
These are new places and new concepts that I had no introduction to in dental school.
00:06:00.143 --> 00:06:14.324
And so I had to figure out what is working and what wasn't working, how that related to the traditional dentistry that I knew that part of the dentistry that I did was called adhesive dentistry.
00:06:14.391 --> 00:06:19.963
But bonding to deaden was not known or taught at all.
00:06:20.062 --> 00:06:22.799
By the year that I graduate in 1978.
00:06:22.799 --> 00:06:26.136
All these things are very complicated chemistry.
00:06:26.136 --> 00:06:40.317
And Bart Van Meer Bik in 1993 wrote his dissertation comparing 20 of those bonding systems, the 20 bonding systems that he used in 1993.
00:06:40.417 --> 00:06:45.388
There's only two that are still produced in the world.
00:06:45.489 --> 00:06:56.365
So there was 10% of the body systems that had something that was good enough that doctors would keep trying and keep using and keep bonding.
00:06:56.466 --> 00:07:08.211
So from 1978 to 1998, 20 years before we got to the self etching solution to the problem of smear layer removal, which we called conditioning.
00:07:08.311 --> 00:07:21.891
And then once we had this self-editing system, we had the ability to understand that we had simplified but not oversimplified, this approach to bonding.
00:07:21.992 --> 00:07:32.968
If we oversimplify by the approach, the bonding, and take the bottle of primer, which is hydrophilic, likes water, and the bottle, he said, is hydrophobic.
00:07:33.069 --> 00:07:47.651
If you do those separately in your priming and then bonding, then the hybrid layer has certain characteristics of a gradient, and that gradient has certain flexibilities as a bottle where it's moist and wet.
00:07:47.651 --> 00:07:54.357
And then other characteristics as it gets towards the surface is going to be restored with the composite.
00:07:54.357 --> 00:08:09.673
So that gradient in this hybrid layer, which was named in 1982 but refined in 1993 by Van mere B when he called it inter diffusion area zones.
00:08:09.739 --> 00:08:19.382
So these inter diffusion area zones that then Meier be identified were called deep, intermediate and superficial.
00:08:19.482 --> 00:08:22.752
In this little logo on a cap, this would be the deep zone.
00:08:22.752 --> 00:08:25.655
This would be the intermediate, this would be the superficial.
00:08:25.655 --> 00:08:36.466
Now, we do have a fourth zone that we'll talk about in our next lecture that gives us the ability to have even a better hybrid layer by not D minerals in any of it.
00:08:36.600 --> 00:08:52.081
The mineral content is removed by this acid etching, which had been Fukuyama's initial innovation taking bone, of course, acid etching of enamel to create these micro grooves that could be bonded to very quickly.
00:08:52.182 --> 00:09:08.197
But Fukuyama, when he uses acid etching, had the unintended consequence, and he understood the consequence of removing too much of the hydroxy apatite that expressed moisture from the vital pulp into the bonding field.
00:09:08.197 --> 00:09:11.368
And that complicates the chemistry.
00:09:11.467 --> 00:09:20.777
So that confounding variable of moisture being introduced from the pulp was eliminated by not etching.
00:09:20.844 --> 00:09:29.619
The dentin and the self etching approach came from the introduction of this molecule tin MDP.
00:09:29.686 --> 00:09:40.663
So once we have a self etching approach and it starts to get tested, then we have the ability to compare tests from different parts of the world.
00:09:40.730 --> 00:09:50.874
The article that I published with five other authors Davey Solomon, Simone Della Perry or out of Herodias Leandro Martinez.
00:09:50.974 --> 00:09:52.175
Felipe Clemens.
00:09:52.175 --> 00:09:58.214
This article was published in 2021 called Decoupling with Time.
00:09:58.214 --> 00:10:07.657
We talk about those different approaches and we identify what is called the gold standard body systems in the world.
00:10:07.724 --> 00:10:31.848
Based on the research that started in 1993 and has continued to this day 30 years later by using a gold standard bonding system, whether you use a total air conditioning or air abrasion conditioning to remove the smear layer, which has always been the weak link of the early bonding systems in the late seventies and early nineties.
00:10:31.914 --> 00:10:38.788
Then we have the ability to say what are our bonds to a flat surface?
00:10:38.888 --> 00:10:45.128
And that last flat surface bonding had been the gold standard for testing.
00:10:45.228 --> 00:10:55.004
And so when we tested those, we had the ability to say on a flat surface we have this amount of bond strength.
00:10:55.004 --> 00:11:01.978
But how many surfaces in a dental restoration, a cavity are flat?
00:11:02.077 --> 00:11:04.447
Well, not many.
00:11:04.447 --> 00:11:08.151
And so starting in 1984.
00:11:08.217 --> 00:11:30.139
So that's four years after Fukuyama says we can bond to dentin, then investigation of bonding to deaden not only on a flat surface, but on a surface that had sides, a cavity preparation that is common in restorative dentistry that started to be experimented with.
00:11:30.206 --> 00:11:35.879
And the experimentations start in Amsterdam with Carol Davidson.
00:11:35.979 --> 00:11:44.620
So Carol Davidson, in 1984 starts the discussion with this paper.
00:11:44.788 --> 00:11:55.498
And this paper is called Relaxation of Polymers Asian contraction stress by flow in dental composites.
00:11:55.598 --> 00:12:00.403
So this is a new term introduced by a team of researchers from Amsterdam.
00:12:00.403 --> 00:12:05.175
Carol Davidson himself was not a dentist, he was a physicist.
00:12:05.240 --> 00:12:12.514
But physicists experimented with products with chemicals and polymerization shrinkage of composites.
00:12:12.581 --> 00:12:28.331
This was an expertise that he had, and he started to test the different composites He had to develop unique apparatuses to measure the stress of polymerization shrinkage.
00:12:28.398 --> 00:12:34.571
The first apparatus that he developed in this paper got to look like a dumbbell.
00:12:34.571 --> 00:12:39.808
So we usually call this a dumbbell apparatus.
00:12:39.908 --> 00:12:44.514
So this is the dumbbell apparatus.
00:12:44.614 --> 00:12:52.020
Now, this dumbbell apparatus has hollow areas inside the top and the bottom.
00:12:52.020 --> 00:12:56.558
And then a hollow area here, and this is filled with composite.
00:12:56.625 --> 00:13:08.805
And then we have ten kilometers on both sides that whereas the compass as it is shrinking, it's supposed to pull these two ends of the dumbbell together.
00:13:08.871 --> 00:13:19.048
Now, the inside of the dumbbells, metal, there's no air abrasion, there's no bonding to do this metal through silent ization techniques.
00:13:19.048 --> 00:13:21.417
It's just holding the composite.
00:13:21.417 --> 00:13:23.786
It's a chemical, pure composite.
00:13:23.887 --> 00:13:40.336
And when they shrink the composite in this dumbbell, it didn't contract as much as they thought it would be because the shrinkage we knew the percentage of the shrinkage of the composite is just on a table and it shrinks.
00:13:40.336 --> 00:13:43.572
You can measure the the volume of the shrinkage.
00:13:43.572 --> 00:13:51.980
But in this contraption device, something happened inside these composites that relieve the stress.
00:13:52.048 --> 00:13:55.918
Now, these early compounds, 1984 are chemical cure composite.
00:13:55.918 --> 00:13:59.489
It takes 5 minutes to get hard.
00:13:59.589 --> 00:14:19.575
That's very important to understand because this mechanical containment of the composite, there was shrinkage of the composite, but only at a certain stage did the composite start to shrink in a way that the tenths alarm emitters started to come closer to each other.
00:14:19.642 --> 00:14:26.215
And so that had to be described and that was described as a free flow condition.
00:14:26.316 --> 00:14:30.552
In other words, the molecules are composite, are coming towards each other.
00:14:30.552 --> 00:14:36.491
They're connected inside of this dumbbell, but they're not connected to the walls of the dumbbell.
00:14:36.558 --> 00:14:45.033
So there's no holding mix with the bond, the walls and all of the movement is the composite molecules moving towards each other.
00:14:45.100 --> 00:14:48.104
So that's called free flow condition.
00:14:48.104 --> 00:14:54.711
And if you have a free flow condition, then there was no stress on these two ends of the dumbbell.
00:14:54.711 --> 00:14:59.414
Whoa, That was something that needed to be known.
00:14:59.481 --> 00:15:16.699
So what they figured out is that if you were holding a mass of composite and you didn't get much stress, it was because these molecules were slipping by each other and are slipping by you know each other means that the cross-linking was at a minimum.
00:15:16.765 --> 00:15:20.769
Once they started cross-linking it about 3 minutes.
00:15:20.836 --> 00:15:25.741
Then they started to have some stress and then a minute for more stress.
00:15:25.841 --> 00:15:28.443
And the most stress was at minute five.
00:15:28.443 --> 00:15:31.447
And that's when the cross-linking was at a maximum.
00:15:31.681 --> 00:15:35.051
And that's called the post gel point of composite.
00:15:35.051 --> 00:15:37.253
It polymerization.
00:15:37.253 --> 00:15:39.755
This was interesting information.
00:15:39.755 --> 00:15:44.259
But then again, how does it apply to actual cavities?
00:15:44.326 --> 00:15:54.269
Well, the application to cavities was investigated three years later by the same group if we now have a constraint.
00:15:54.269 --> 00:16:09.719
So they made this machine, unlike the dumbbells, this had two flat plates and the food two flat plates now had columns of composite that were connected to the two flat plates.
00:16:09.818 --> 00:16:11.653
They were bonded to those flat plates.
00:16:11.653 --> 00:16:24.399
So there wasn't a a free flow, but they actually had in between these two flat plates, this composite was shrinking, but it was connected to both plates.
00:16:24.466 --> 00:16:47.090
And so what they found out is that in that situation where you are constrained on one side or on both sides in this situation, then the amount of composite that you had in between those two plates had a relationship on how fast and how strong the stress was going to be.
00:16:47.090 --> 00:16:48.925
In other words, the plates are like this.
00:16:48.925 --> 00:16:51.159
You got a composite column here.
00:16:51.159 --> 00:17:00.702
Once that chemical Kier Composites starts connecting in that 3 minutes, 4 minutes, 5 minutes, then these plates are moved towards each other.
00:17:00.702 --> 00:17:07.009
That sense by the ten kilometer on each side, and that starts pulling them towards each other.
00:17:07.009 --> 00:17:08.211
Okay.
00:17:08.211 --> 00:17:24.559
If they held the plates so they could not move, then the only thing that would happen is that the composite would have the movement of the composite molecules just like it was shown in the first experiment.
00:17:24.659 --> 00:17:30.031
And so if you had a large column of composite, there wasn't much stress.
00:17:30.132 --> 00:17:37.973
If you had a short column of composite, then the cross linking happened percentagewise much more rapid.
00:17:37.973 --> 00:17:40.709
And so that caused more stress.
00:17:40.709 --> 00:17:48.750
So they were able to calculate the surface area of the two round plates and the surface area of the unborn, a composite.
00:17:48.850 --> 00:17:55.557
And if they had a large surface area of onboard a composite, then there wasn't much stress on the plates.
00:17:55.657 --> 00:18:07.802
So the ratio of bonded to on bonded surfaces became the definition of see factor configuration factor.
00:18:07.936 --> 00:18:16.211
Every textbook talks about configuration factor every year, peculiar talks about because configuration factor.
00:18:16.278 --> 00:18:41.169
None of them have explained it to the way that they needed to explain it, because I actually read these articles in detail and I understood that, for example, if you have no bond to your apparatus or a cavity, then all the shrinkage moves in one direction.
00:18:41.236 --> 00:18:42.804
And so that's called free flow.
00:18:42.804 --> 00:18:54.216
In this experiment, it was not free flow because we had bonded surfaces here and bottom surfaces here, but the flow is happening in the unbounded composite.
00:18:54.282 --> 00:19:01.623
So there was things happening in the composite movement as the column was large compared to when it was thin.
00:19:01.690 --> 00:19:07.096
And we had a lot of cross linkage percentage wise happening earlier.
00:19:07.163 --> 00:19:21.109
What that meant is that if you eliminate the free flow, then you have to say, what kind of influence do you have on the bonded surfaces in this situation?
00:19:21.176 --> 00:19:24.179
Bonding to metal with the composite is very easy to do.
00:19:24.379 --> 00:19:30.252
There's no moisture, there's no collagen, there's none of the slippery or flexible characteristic.
00:19:30.252 --> 00:19:32.788
Six of of dentin.
00:19:32.788 --> 00:19:35.323
So these have 100% bond strength.
00:19:35.323 --> 00:19:40.428
And so we've eliminated the hybrid layer development.
00:19:40.428 --> 00:20:00.282
And as a confounding variable in these shrinking composites, the hierarchy of bond ability was a concept that I introduced to explain then why these experiments can't be directly used to understand how composites work in cavities.
00:20:00.348 --> 00:20:14.329
But the next published paper that was published again in 1984 had another device that they had to invent and this device is this little jig here.
00:20:14.396 --> 00:20:18.867
So we have a tense laminar on one end, tense laminar on the other end.
00:20:18.967 --> 00:20:20.269
We have dentin.
00:20:20.269 --> 00:20:23.705
This little triangle piece here is dentin.
00:20:23.772 --> 00:20:28.276
And then we have the the column of composite that's on top of it.
00:20:28.343 --> 00:20:32.447
Now, the top of it that holds the composite is being bonded to.
00:20:32.447 --> 00:20:34.482
Then again, this is a free flow.
00:20:34.482 --> 00:20:36.184
That is the core situation.
00:20:36.184 --> 00:20:40.121
There is no bonded surface to this metal.
00:20:40.188 --> 00:20:41.156
And so it's just bond.
00:20:41.156 --> 00:20:42.324
It's a deaden.
00:20:42.324 --> 00:20:50.899
And this free flow means that the unidirectional bond will move towards the dentin.
00:20:50.965 --> 00:20:59.140
And they were able to get bond strength at about 19 mega pascals in 1984.
00:20:59.207 --> 00:21:08.183
So here we have a free flow condition on top, but a constrained condition only on the bottom.
00:21:08.283 --> 00:21:27.936
That's different than the experiment that established the idea of C factor, where you have two constraints, then you have no difference in bond ability between different areas of the of the shrinking composite.
00:21:27.936 --> 00:21:40.215
But then when they took that idea and put it into a three dimensional cavity, they came up with this result.
00:21:40.215 --> 00:21:47.288
So here we had a now a three dimensional cavity that we had some constraint here.
00:21:47.288 --> 00:21:52.527
Constraint here, constraint here, meaning it was bonded to enamel, bonded to enamel here.
00:21:52.527 --> 00:22:04.038
But then as we got down here and we were bonding it to dentin, as they did the experiment, but they never had a lamination of the enamel on either side.
00:22:04.105 --> 00:22:09.244
They had very little d lamination in certain areas that were right next to the enamel.
00:22:09.244 --> 00:22:26.661
This is called superficial dentin, but the main gap that was formed was always in this deep area, which we called intermediate dentin or even deeper dentin, as it goes to 2 to 3 millimeters deeper past the DG.
00:22:26.761 --> 00:22:29.764
So this is what they showed.
00:22:29.831 --> 00:22:46.981
And then six years later, one of Kiel Davidson's graduate students, Chantelle Kemp's Shorty, did another experiment trying to solve that problem of how to prevent that D lamination in the bottom of the cavity.
00:22:46.981 --> 00:22:49.751
And they started to experiment with different liners.
00:22:49.751 --> 00:22:54.055
The only liners that had any success were composite liners.
00:22:54.055 --> 00:22:56.291
There was no flowable composite at that time.
00:22:56.291 --> 00:23:08.336
It wasn't invented yet, but they did have some less viscous liners that work, and those liners had the ability to have some sealability.
00:23:08.436 --> 00:23:12.875
That was published in 1990, another paper that's been forgotten.
00:23:12.942 --> 00:23:24.086
But when I read that paper at this time, I'm trying to think now these composites are basically the same as the liners.
00:23:24.319 --> 00:23:26.621
That doesn't make sense.
00:23:26.688 --> 00:23:34.163
In other words, you get a gap formed with the composite and you have something like the composite and you get less of a gap.
00:23:34.229 --> 00:23:37.031
What's the difference?
00:23:37.031 --> 00:23:45.740
And in my mind, you know, which is a little bit out of the box thinker, I'm trying to, you know, discover things that that I don't understand.
00:23:45.840 --> 00:23:53.314
It gave no mind that it took time to put these liners onto that floor and the composite liners that did the best.
00:23:53.381 --> 00:23:56.584
It took a little bit of time to adapt them.
00:23:56.651 --> 00:24:04.325
And I was enough of a chemist to know that every chemical reaction has a beginning, a middle and an end.
00:24:04.392 --> 00:24:09.430
And so I related, as I discovered this this paper was published in 1990.
00:24:09.564 --> 00:24:13.101
The other papers were 1984, 1987.
00:24:13.167 --> 00:24:20.141
I remember I didn't start investigating any of this until 1995, so I had to go back and find these papers.
00:24:20.141 --> 00:24:23.811
I had to get these papers from other references, from other articles.
00:24:23.913 --> 00:24:30.285
That was important, but not clear in the later articles that were published.
00:24:30.285 --> 00:24:41.896
Later articles would talk about C factor, later articles would refer to flow, but they didn't really start coming together until 1980.
00:24:41.896 --> 00:24:56.311
So in 1999, 2000, 2002 and in those years, then we started to have some real research that gave us the combinations of these approaches.
00:24:56.411 --> 00:25:31.212
And so the concept that came into my mind and it was stimulated more by Carel Davidson than any anyone else, because this idea of composite movement, when Cho investigated this and and published his research, there was also something that I learned in 2000 from my second mentor, Gary Unterbrink, who was speaking at a lecture set up by my first mentor, Ray Bertolotti This was in 2000 and I wrote this in my notes and it said, Composites move towards the best bonded surface.
00:25:31.279 --> 00:25:36.150
And so my first mentor, Ray Bertolotti introduced me to the concept of C factor.
00:25:36.150 --> 00:25:38.219
I did hear that first from him.
00:25:38.219 --> 00:25:42.123
Gary Unterbrink The idea of flow and of the composites.
00:25:42.123 --> 00:25:52.900
He was referring to that, but he was not understanding that how it directly related to an indirect restoration or a direct restoration.
00:25:52.900 --> 00:26:01.209
And so the time elements of how the composite flow moves early on is something that I had to figure out.
00:26:01.242 --> 00:26:07.849
And there were many papers being published and they would have graphs like this graph.
00:26:07.915 --> 00:26:13.454
You can see this has a beginning and end and this is the polymerization that's going like this.
00:26:13.454 --> 00:26:35.343
And the numbers that are down here at the bottom were significant because there was always in this first 3 minutes of very strong polymerization starting and the strong polymerization was much stronger with the Camphorquinone like cured composites that were now being investigated in the late eighties, early nineties and then into the nineties.
00:26:35.343 --> 00:26:53.027
The Light cure composites basically took the the field of dentistry by storm, created graphs like this was published this one was published in 2004 by him out of University of Colorado, Lou Stansbury and Bowman.
00:26:53.094 --> 00:27:07.008
And this is the graph and this I say has been shown over and over again if you have a light, your material, then you have a time of very rapid polymerization beginning and then it plateaus.
00:27:07.075 --> 00:27:09.777
The polymerization actually lasts.
00:27:09.777 --> 00:27:14.215
Molecules are still polymerization at 24 hours.
00:27:14.315 --> 00:27:20.688
A few molecules are reacting to these free-radical polymerization connections.
00:27:20.755 --> 00:27:34.135
But in a direct composite, you have about 60 to 65% of the monomers that are glamorized after 10 minutes and then the rest are polymerization and small amounts.
00:27:34.235 --> 00:27:43.111
But this early polymerization, what we call the beginning of the plateau, is always at 5 minutes.
00:27:43.211 --> 00:27:51.052
And so that led me to the conclusion that you have this five minute window where a lot of polymerization happening.
00:27:51.119 --> 00:27:58.493
The stress only comes from the polymerization and the polymerization has to be connected to walls.
00:27:58.593 --> 00:28:15.276
So we have some constriction when we have walls, but the polymerization of multiple walls only starts to effect the hybrid layers at that early five minute situation.
00:28:15.276 --> 00:28:22.917
So this is developing in my mind between the years 1998 and 2004, really.
00:28:23.017 --> 00:28:31.526
And in 2004, a landmark paper that was published, we call Nikolaenko 2004.
00:28:31.626 --> 00:28:37.498
And in that paper it gave us real numbers using gold standard bonding systems.
00:28:37.598 --> 00:28:45.373
On how C factor affects the bond strings of these restorations that are adhesive restorations.
00:28:45.373 --> 00:28:58.686
The title of this paper is The Influence of C Factor and Layering Technique on Micro Tensile Bond Strength two then 24 published in the journal Dental Materials.
00:28:58.753 --> 00:29:26.013
And what Nikolaenko found is that if you have a thin layer that's horizontally placed in the deep part of the cavity or you got a four by 4x4 cavity shape, if you do one millimeter and then the second millimeter and then the third millimeter, and then the fourth millimeter, the bond strength at the bottom of the preparation next to the pulp is doubled.
00:29:26.013 --> 00:29:33.855
If you bulk fill that 4x4 by four, then you lose 80% of your bond strength.
00:29:33.921 --> 00:29:53.942
And so the number that they came up with, with this one millimeter horizontal layering was 30 megapacals using a gold standard bond system like off the bond fell and that 30 megapascals all became very important because that is the cohesive strength of enamel.
00:29:54.041 --> 00:30:16.731
So if we can't connect these deepest parts of the tooth at the same strength that enamel is connected to each other, we call that mimicking the strength of a natural tooth or Biomimetics definition is connecting you to side to side, front the back and top the bottom around 30 Megapascals the same as cohesive strength of enamel.
00:30:16.798 --> 00:30:40.154
So with that then we had the time element and the thinness element of a layer confirming what was published two years before in the Deliperi Bardwell paper that gave us the idea of a stress relief by limiting the volume of the increments that are placed on top of the hybrid layer.
00:30:40.221 --> 00:30:44.992
So that's the end of this episode.
00:30:45.126 --> 00:30:50.898
We will continue talking a little bit more about this next time.
00:30:50.965 --> 00:30:52.300
Get bodied, stay bonded.
00:30:52.300 --> 00:30:53.467
Always great talking to you.
