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Well. Good morning.
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We're very excited to do episode 11, immediate dentin sealing .
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We'll be highlighting this paper that was written in the year 1997.
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That's not a long time ago if you're 72 years old, but for many of you, that will seem like a long time ago.
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The topic today of immediate dentin sealing has probably become the most talked about aspect of biomimetic restorative dentistry.
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Obviously, Doctor Pascal Magne has been very prominent in promoting that concept, but the history of immediate dentin sealing goes way back, and the early origins of that are important.
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They come from two different universities.
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One university is Tokyo Medical and Dental University that we've talked about in the past, and we've talked about how important it was to develop the caries detecting dye and the techniques of understanding the different layers of dentin that are affected by decay.
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The most common pathology and so Fusayama’s position as the father of adhesive dentistry, also becomes the father of biomimetic dentistry.
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Because without adhesive dentistry, we can’t have biomimetic dentistry.
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But beyond that, without caries removal end point consistency, we can’t have predictable adhesive hybrid layers established and so after we’ve talked about caries detecting dye caries diagnosis and treatment, selective caries removal versus total caries removal to protect the pulp.
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And then the last two lectures we’ve talked about cracks and gaps and how they allow infection.
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The cracks and gaps are a pathology that endanger the pulp.
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Decay, obviously, is a pathology driven by the presence of bacteria in the decay process.
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But once we've treated those two pathologies with selective removal so that the pulp can heal, now we're starting the rebuilding of a biomimetic restoration.
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My son Davey, who's been teaching with me for 12 years, coined the phrase that the six lessons approach is a bottom to top approach.
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Most dentists like to look at pretty tops.
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It's a human thing to look for beauty, but if you're looking at the top of the tooth, you're not really understanding the unique characteristics of a tooth that allows it to distribute forces of occlusion throughout the whole tooth, and that connection of the whole two side to side, front to back up the bottom can only be accomplished when a strong hybrid layer is established, connecting the tooth to the materials that are restoring the missing parts of the tooth that have been destroyed through pathology.
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And so when Fusayama started to investigate bonding to dentin the interaction was not understood.
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But soon it was connected with early bonds to enamel that were understood and had been established in the mid 50s by Michael Buonocore.
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Michael Buonocore was using a bonding system called sevreton and sevreton had the ability to polymerize, and these polymerization the molecules that polymerize with etched enamel that was born, of course, huge breakthrough to surface condition the enamel so that there were micro porosity that could be engaged by the polymerize in composite.
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The polymerization composite was actually not a composite, it was a polymerization poly methyl methacrylate.
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So poly methyl methacrylate works great.
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It has a lot of shrinkage.
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We've been using it since the 30s very effectively.
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And epoxies and various materials that we would call plastics.
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But the shrinking of plastics, if they're done outside of a situation, can be controlled.
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If you're molding something and you have a mold and you say, okay, we're going to have 7% shrinkage is small, then after the shrinkage has happened in the plastic, you look at it and say, that's the size that we have.
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So that shrinkage that happens inside of a mold is not a negative thing.
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Because now you have the item that can be used with the shape that it has.
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It's a very different situation.
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When we start polymerizing materials in what we call in situ in the actual body.
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And so that shrinkage that happens inside the hybrid layer of enamel, it wasn't really appreciated because there was a high connection with enamel, because it was a dry material.
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But from the mid 50s until 1975, for 20 years, bonding to dentin was not in any way predictable or consistent until a new chemistry was established and that new chemistry was established at Tokyo Medical and Dental University, and that chemistry took a molecule and that molecule, instead of having two ends that were hydrophobic, which is the case with all epoxies and all poly methyl methacrylate polymerizations those molecules now were divided into an end that had a hydrophilic molecule attached to it.
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And so the hydrophobic, in which most plastic engineers are expert at this is now called a bipolar molecule.
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So the bipolar molecule the first one that was made was very short.
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It had an end that was hydrophilic, which is called phenyl end and then an end.
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That was the methacrylate end.
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And that poly was called phenyl-p molecule was first introduced from a team of scientists who were working at Tokyo Medical and Dental University from a company called Kuraray, Kurashiki Rayon, Kuraray They had chemists that knew about polymerization molecules, and they knew in this chemistry that they had a very difficult challenge to bond to dentin, the bond to detonate.
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We referred to earlier from this material.
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They came from a Swiss chemist named Oskar Hager and then made into a dental filling material in England had terrible results because although it could go from a soft to a hard state, that's called polymerization.
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It had the shrinkage of a polymer of a factor rate, which is about 778%.
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And so this created a gap.
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But the bond to dentin which we referred to in the earlier lectures, which was an unintended consequence, there was a nitric acid contaminant in the synthesized molecule of the GPDM which was the molecule they were polymerized in, which came from the epoxy.
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That history we've referred to it.
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It was a failure that didn't work as a dental restorative material And so when it was revisited by the Japanese, they had a very important insight.
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And that insight was that in dentin we have to work with the water.
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20% of dentin is water.
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Now, the 20%.
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This water is also integrated into a matrix that is built by collagen that's encrusted by hydroxyapatite.
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So we have three elements.
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There are moist, one stiff and one's flexible.
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And so the chemists at Kuraray made this molecule phenyl P.
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And this was the first molecule that fusion was able to see on a flat surface at a bond to dentin.
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But he had to use a phosphoric acid to condition the dentin Just as the phosphoric acid had been used.
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It used in 1955 by Michael Buonocore to condition and makes the micro grooves into the enamel well.
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Fusayama when he saw this in a demonstrated even though the bond strengths were low in the four or six, maybe eight Megapascal range, he knew that it was an important breakthrough, but he always felt like this interaction of a positively charged end of a molecule and a negatively charged end of a molecule had something to do with the chemical interaction, and the chemical bonds that he believed were established could not be proved at that time.
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The type of bonding there's two types of bonding that we're talking about here would be an ionic bond and then a cohesive bond or a covalent bond.
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I should say covalent bond and ionic bond can give cohesive strength.
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A crystal, for example, is totally ionic bonding, and it has cohesive strength.
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It's usually brittle, like hydroxyapatite.
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But then the bonds that are covalent bonds, which are stronger, are also part of the depth and complex in the collagen, which has covalent bond in that holds the molecules of the protein of the collagen molecules together.
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So when this phenyl P was synthesized, they had the initial success and an initial insight, and it was investigated within four years of this synthesis.
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1978 to 1982, by another doctor, but not a doctor of dentistry.
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At TMDU, he was a chemist, so he had a PhD in chemistry.
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His name is Nobuo Nakabayashi.
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He passed away last year, but Nakabayashi started to synthesize other molecules and he also started to investigate with scanning electron microscopy and with transmission electron microscopy.
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These connections between the composite and the dentin And that was his life's work.
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My good friend Charlie Cox, who knew knuckleball as you well, spoke Japanese, but the brilliance of his chemistry could be reproduced, and his investigation through microscopy was exactly Charlie Cox's expertise.
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Charlie Cox, the histology, and Charlie Cox knew about preparations of specimens for light microscopy and for electron investigation on a scanning electron, and eventually transmission electron microscopy, and the connections between the materials in the body of the two became known and were named by Nakabayashi The hybrid layer because a hybrid not composite, not tooth.
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It was a combination of those two, so Nakabayashi naming of hybrid layer starts in 1982, but the investigation of that hybrid layer took years to get to the position where we understand exactly what's happening and that and understand in was given huge scientific validation or understanding.
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In 1993, ten years after the hybrid layer was established, Bart van Meerbeek did a four year PhD at Catholic University in Leuven, Belgium, investigating the hybrid layer in the interactions and the interactions with many dentin bonding systems.
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Here's a page from Van Meerbeek’s dissertation.
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This dissertation lists over 20 bonding systems, actually 30 bonding systems that were investigated by Bart Van Verbeek in 1993.
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Each of those 30 systems have proprietary chemistry.
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In other words, the recipes of the chemists of each of the different companies Biscoe, Bayer, Kuraray, Kulzer, DenMat, Coltene, Shofu, Johnson and Johnson, generic, Pentron, Kerr, SB Caulk Lee pharmaceuticals, 3M.
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Sun Medical, DMG Vivadent, denmat Tokoyama GC Kerr I mean these are companies who are making products and selling them to dentist to make dentistry better.
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And this idea of adhesion making dentistry better was the initial insight from Fusayama but they actually put it into practice.
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There are many concepts that have to be understood in this interaction.
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The hybrid layer.
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Van Meerbeek was able to break it down into three layers.
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He called them inter diffusion zones.
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You had a top middle and a bottom, not very sophisticated, but the bottom was closest.
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The dentin.
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The top is closest to the composite.
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But these three layers of these inter diffusionary zones add the ability to connect with these polymerize in molecules in different ways.
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The bottom zone was always the most important for its strength, but also the most contaminated with water.
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The middle zone a little of each, and then the outer zone was mostly composite, had high bond ability, but this connection of these three layers, to identify those and to know that this is where the strength came from.
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Huge insight.
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And Van Meerbeek, this is 2024.
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So for 30 years, Bart van Meerbeek has been collecting with his team data on the hybrid layer data on different bonding systems from different companies evaluating those systems and how they interact and form this connection with the tooth, the hybrid layer.
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In 2009, a fourth dimension of the three layers of the hybrid layer was added.
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That fourth dimension is called the acid base resistance zone, sometimes referred to as super dentin named by Tagami when he announced it at the International Association of Dental Research in Miami Beach.
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I was sitting next to Simone Deliperi at that meeting.
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400 dentists were listening to this breakthrough information, but this area that was below the hybrid layer, in other words, this was in dentin said that some molecules that had been introduced in 1989 was the first invention of this new molecule.
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They had the ability to like snakes going underground, getting into the dentin, and they could go in these little channels that were micro channels filled with this 20% of water.
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And then for one micron or even two microns below the hybrid layer, this acid base resistance zone, which the gummy called super dentin because they found out that once the polymerization of these four into diffusion in your layers was made, you could not dissolve this dentin that had been infiltrated through the hybridization process.
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But the molecule that achieve that was not phenyl P, the molecule that achieved that was in collaboration with the two organizations Kuraray and TMDU.
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The chemist was named Omura, and Omura had the ability to understand that well, if you're trying to separate water loving elements of the hybrid layer from water hating elements of the hybrid layer in this inter diffusionary zone, hydrophobic, hydrophilic.
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If you had longer molecules, then you could allow the water to come in and be encapsulate it by these molecules very easily.
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And so they made the molecule longer.
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And so it was actually about three times as long as the phenyl p.
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And this length of the molecule, which was called 10 MDP, allowed it to have interaction with water in this area in between the part of the molecule that didn't like water and the part of the molecule that liked water.
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And so it worked very well in this gooey area that's been polymerize and taken from a watery state to a dry state in the hybrid layer.
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But the thickness of that hybrid layer.
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Traditional hybrid layers were investigated and thought to be five microns thick, and they showed invagination of the composite resin into the tubules.
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And these little projections of the resin in the tubules were called tags.
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And they were thought to be very important as far as the strength.
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The longer the tags into the tubule, the more strength of your resin infiltration.
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Turned out that was totally an artifact.
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It wasn't true at all.
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And actually, Fusayama in his books in 1980 and 1993, I'm not sure there was in 1980s book, 1993.
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I know that it's there.
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Showed that in a hydrating pulp, you have a whole fluid that's been pumped regularly with the heartbeat, and that's preventing any infiltration of the resin into these tubes.
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Of course, it would be different in a non vital tooth.
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You can get a tag into an end, wrongly treated tooth, and all of the teeth that were being tested at that time were extracted.
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Teeth did not have pulps with vital fluid, and so the resin tags, you know, they were kind of looked sexy, but they didn't mean anything.
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But I can remember as I was a dentist trying to figure these things out in the 80s, getting more and more confused every year that things came out because these bonding system did not work, even though companies promised me that they were working in their body to then these were very, very weak and restorations required retention form, resistance form.
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All of the traditional mechanical retentive forms of the cavity were necessary to make these adhesive systems work.
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They weren't they weren't adhesive.
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As we start talking about this connection, and once we establish and this happens about 1998, 1997, where we actually have a dental bonding system that has a combination of phenyl P and 10 MDP, it's called liner bond two.
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And that system in in vitro tests is like triple the strength of other systems before.
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And there's many things that go into that.
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We talked a little bit earlier in a lecture about the Liner Bond Original System liner bond one, which was developed by Hosoda and Hosoda at the insight that we had to get rid of the smear layer.
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But then once we got rid of the smear layer, we had a collapse of the collagen.
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So we had to prime the college and to puff it up a little bit.
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And then we could use a moderately effective bonding system that did have ten MDP called photo bond, but the only way it really worked on a vital tooth is to immediately put a a, a layer of a flowable composite.
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And that flowable composite, was the protect liner f the first flowable composite in the world.
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Anyway, there were many steps in this liner bond system.
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The liner Bond two system was much simplified because it had an exclusive primer and bonding system that was based on this ten MDP.
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Other molecules in the primer like Hema, and other molecules in the hydrophobic end like Bis-GMA and Tegma Those are proprietary mixtures that each company has.
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But the companies that had monomers that weren't as good as the ten MDP or as polymerizable as the GPDM, which turned out to be another strong candidate for a gold standard bonding system.
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Other companies tried other molecules and they tried other combinations of conditioning acids.
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They tried other combinations of solvents.
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Acetone became very popular.
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Ethanol, water.
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All of these proprietary recipes have an effect on the hybrid layer establishment, and the hybrid layer establishment, once it's in place, becomes the first layer of connection.
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But that layer of connection has to be connected with the rest of the restoration.
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Well, in Japan, there were many investigators using these early systems and found that they did work and they were having success in vital teeth even on pulp exposure.
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Research was done by Kashiwada in 1991.
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Kashiwada did direct bulk caps on real people with these early bonding systems.
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And then we had a study in 1994 on an indirect technique.
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And in this indirect technique, we had, through Sato, an establishment of a superior result.
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This is a clinical trial using this idea of what we call now immediate and ceiling.
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It wasn't called that then.
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What it was called is using liner bond system as dentin and pulp protector in indirect restorations.
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So that's called immediate dentin sealing in 1994.
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But within two years, researchers at another outstanding research institution led by their director, who was named Peter Scharer at the University of Zurich, had another article published.
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And in that article, we had the ability to compare the results coming from Japan and the results coming from Europe.
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And the authors of this Christian Bertschinger was the lead author.
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Stefan Paul was the second Heinz Luthy, and then Peter Scharer is the final author, the one directing the research at University of Zurich.
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When they published this article in 1996, and then they followed up with the article that I first read that led me to understand that this was something very important.
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So this is 1997.
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So now we have actually a name for this idea of doing a bonding step initially at the preparation stage and then doing a bonding step at the cementation stage.
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Now they called it dual bonding, but they were trying to solve a problem that did not relate to the strength of the bonds.
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Their problem that they tried to solve with that paper was contamination of dentin by tamper resistant materials, which were almost always eugenol based.
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And so they knew that if they had eugenol, contamination, the polymerization of the GPDM molecule, or the ten MDP molecule or the molecule that was synthesized by Biscoe in all bond two was successful.
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Molecule.
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Also, they understood that this eugenol interfered with the chemical reaction, and so the polymerization was weakened or even completely negated by eugenol.
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So their idea was how about if we sealed the dentin Dentin doesn't get contaminated by eugenol, and then we can put the temporary restoration in, and then it's easier to clean off this eugenol, because now we have this adhesive layer that's been polymerized that protects this from the contamination.
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That was the problem they were solving.
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And they had better success because now they had bonds that were bonding to the dentin.
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And the sensitivity that was endemic on direct and indirect restorations was being solved by using these better bonding systems in the 90s.
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But the strength of the bonding systems that were coming out of these earlier Kashiwada or Sato from Japan.
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Paul and Scharer and Bertschinger out of Switzerland.
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The bond strengths were still low and so all of the details of the chemistry in many systems were not being progressive.
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But when the who are a company in 1997 came out with this line or bond two system, it was considered a self etch system.
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And so no phosphoric acid conditioning, removal of the smear layer was needed to get higher bond strength, and the higher bond strength they got were around 20 mega pascals, which were twice as strong or three times as strong as the early systems.
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that the Van Meerbeek tested in 1993 that were developed in the 80s.
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And so this self etching system now, it was a simplification, but it also didn't give us the exact numbers that they were using to have these successful in vitro clinical trials that they ran from 1997 to 2007, saying that these restorations are functioning successfully.
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They're not showing signs of leakage or decay fracture.
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So this in-vivo study that was done by Yasuko Momoi and Naotake Akimoto ten year in vivo study takes a lot of time, a lot of effort, a lot of resources there.
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When that came out and published in 2007, it changed the world for people who are paying attention.
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But we also had to understand how a direct restoration or an indirect restoration differ, and how the structure of the tooth differs.
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And so these concepts started to be followed in the 90s, and then during the 2000s, which is now still or 2024, but in the early 2000, technologies to make indirect restorations more chair side friendly.
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We call that technique a semi direct technique, which was first introduced with chair side inlays on lays at Creighton University, but did not work even on the polymerization of the material, was done outside of the restoration, so that shrinkage didn't affect it.
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There was a problem when they tried to bond that restoration that had no shrinkage, but they had not dealt with the idea that in the hybrid layer itself, there is shrinkage in the hybrid layer.
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That itself there is a polymerization that has to be maximized.
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It has to be used to strengthen the hybrid layer.
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And so when Dietschi and Spreafico published their book in 97, they didn't have this figured out.
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They had the idea of a semi direct restoration not causing polymerization shrinkage because it's polymerized in outside the cavity.
00:26:45.721 --> 00:26:58.866
But then they didn't have figured out that they had to hybridize the dentin or what Pascal likes to call immediate dentin sealing, and we all call it immediate dentin sealing now but Doug Terry used to call it pre hybridization.
00:26:58.866 --> 00:27:03.838
Bill Liebenberg also called that pre hybridization in 1999.
00:27:03.838 --> 00:27:16.951
But the idea of in an indirect restoration or a semi direct nearside restoration to have a maximum interaction and bond strength, you have to hybridize the hybrid layer first and then wait a period of time.
00:27:17.285 --> 00:27:24.625
It may be 30 minutes to make the steric restoration, or maybe two weeks if the lab is making your indirect restoration.
00:27:24.625 --> 00:27:47.648
But the idea of this dual bonding means that there is a separation in time between the hybridization of the dentin and the cementation and that was a critical insight that came from the University of Zurich and Peter Scharer when he published these two papers Stefan Paul, when he published coauthor on those papers had that insight.
00:27:47.648 --> 00:27:49.751
But how does that insight get out?
00:27:49.751 --> 00:27:52.987
How does it spread from one university to another university?
00:27:53.154 --> 00:27:56.724
Well, if you're in Switzerland, it's easier than if you're in California.
00:27:56.724 --> 00:28:12.306
But eventually Stefan Paul left University of Zurich and went to UCLA in California, where I grew up, Los Angeles, and he was at the University of California, Los Angeles, same time that Charlie Cox was at the University of California at Los Angeles.
00:28:12.306 --> 00:28:33.761
And when Charlie Cox understood and Stefan Paul understood, and these concept of immediate dentin sealing before a restoration was bonded, the tooth had to do with the polymerization of the cement and the polymerization of the cement is going to move because all polymerization materials move.
00:28:34.163 --> 00:28:39.467
In other words, whenever you have shrinkage, if there's no walls, the shrinkage goes towards the center.
00:28:39.600 --> 00:28:43.137
If it's bonded towards one wall, then the shrinkage can go here.
00:28:43.337 --> 00:28:57.852
But if there's two walls and you have a layer of cement shrinkage, the cement has to decide am I going to stay where I am and have equal movement towards both walls, or am I going to move towards one wall at the expense of one wall?
00:28:58.052 --> 00:29:01.823
And what that is called is the hierarchy of bondability.
00:29:02.056 --> 00:29:17.071
If you have one wall that's drier and more acceptable to polymerization immediately, versus one wall that's moist and flexible and has a little bit of slipperiness, then the shrinkage is going to move towards the dry wall, which would be the restoration.
00:29:17.238 --> 00:29:20.975
And that cement will pull away from the dentin surface.
00:29:21.375 --> 00:29:27.115
And so the concept of hierarchy bond ability was developed by myself.
00:29:27.215 --> 00:29:33.621
And that was trying to solve the question of why this dual bonding system worked.
00:29:33.988 --> 00:29:41.295
And the other systems that were used, but not from the University of Zurich, didn't work well.
00:29:41.562 --> 00:29:52.573
The hierarchy of bondability can be applied to why does bonding to carious dentin work, or why it doesn't work if it's connected with a layer of composite?
00:29:52.573 --> 00:29:57.879
That's too thick, too soon in the polymerization of the hybrid layer.
00:29:58.145 --> 00:30:06.888
And so the hierarchy vulnerability is overcome using the dual bonding technique, which we now call the immediate dentin sealing technique.
00:30:07.288 --> 00:30:13.294
It works because time is put into the restorative process.
00:30:13.561 --> 00:30:21.669
And that time, if it allows the hybrid layer to mature all of a sudden, negates this hierarchy bond ability.
00:30:22.003 --> 00:30:33.714
In other words, if this is an immediate, then seal and resin coated surface, and this is the integral surface of a restoration composite or a silanized ceramic.
00:30:33.714 --> 00:30:37.451
These are both bonded at the same rate.
00:30:37.718 --> 00:30:39.221
They're both dry. Now.
00:30:39.221 --> 00:30:45.059
The hierarchy of bondability has been neutralized by immediate dentin sealing and resin coating.
00:30:45.059 --> 00:30:49.163
And so now we only have to worry about moving through shrinkage.
00:30:49.163 --> 00:30:55.336
These two surfaces closer together, which can happen, is usually a good thing if we have a lower C factor.
00:30:55.503 --> 00:30:59.607
But the other thing that can happen is you can have a strain in a tooth.
00:30:59.607 --> 00:31:09.350
And so in a large restoration which you have a thin cusp onlaying, a thin cusp can allow that movement to move in one direction instead of moving in two directions.
00:31:09.350 --> 00:31:28.869
But again, if the hierarchy of bondability of the whole surface of the cavity is neutralized, so that now all surfaces are basically bonding at the same rate as enamel bonds, then you can only have a slight movement, perhaps, of your two structure or a slight derangement of your polymerize in cement layer.
00:31:28.869 --> 00:31:34.108
But these are all small stresses compared to the stress of the hybrid layer.
00:31:34.108 --> 00:31:41.048
If it's early in the formation, it's detrimental to the tune, usually of 80% of the strength.
00:31:41.048 --> 00:31:49.824
The hybrid layer is lost in a bulk fill restoration, for example, and so immediate dentin sealing that comes from Japan and comes from Europe.
00:31:49.824 --> 00:31:57.465
From TMDU and from University of Zurich are the breakthrough that allow these CEREC restorations, for example, to be effective.
00:31:57.465 --> 00:32:02.203
And once the dual bonding technique was applied with CEREC you had a winning combination.
00:32:02.336 --> 00:32:12.413
The hierarchy of bondability was neutralized, and with the CEREC you had the polymerization which is needed, which we call the decoupling with time step.
00:32:12.413 --> 00:32:15.750
At about 30 minutes, it took about 30 minutes to design and mill.
00:32:16.050 --> 00:32:42.410
All of these add up, and they build upon the idea of getting an ideal caries removal point so that you have a maximization of the bond strength of the surface that you're trying to bond your restoration to, to this cumulative understanding of adhesive systems, the hybrid layer polymerization dynamics, polymerization shrinkage, strain on the tooth, amount of strength that we get from using this.
00:32:42.610 --> 00:32:47.815
All this research kind of culminated 2005, in a paper that Pascal Magne wrote.
00:32:47.982 --> 00:32:54.088
And in that paper, he had numbers that nobody else had been able to to come up with.
00:32:54.188 --> 00:33:02.096
And those numbers in this paper, this is 2005, published in the Journal of Prosthetic Dentistry, gave us exact numbers.
00:33:02.229 --> 00:33:23.918
If you do immediate dentin sealing and bond a indirect restoration to that surface versus an indirect restoration bonded and cemented at the same time, which is called delayed dentin sealing IDS versus delayed dentin sealing showed an increase of bond strength with IDS 400%.
00:33:23.984 --> 00:33:41.635
So we're getting bond strengths instead of in the 11 range in the 50 and 60 range, and the 50 and 60 range is the number we love, because the tensile strength of the DEJ is 51.1, as measured in 2000 by Urabe and the other members of the team TMDU.
00:33:42.069 --> 00:33:44.038
Anyway, a lot to think about.
00:33:44.038 --> 00:33:45.473
Till next time, stay bonded.
00:00:26.242 --> 00:00:27.076
Well. Good morning.
00:00:27.076 --> 00:00:31.948
We're very excited to do episode 11, immediate dentin sealing .
00:00:32.649 --> 00:00:38.088
We'll be highlighting this paper that was written in the year 1997.
00:00:38.421 --> 00:00:46.362
That's not a long time ago if you're 72 years old, but for many of you, that will seem like a long time ago.
00:00:46.697 --> 00:00:55.204
The topic today of immediate dentin sealing has probably become the most talked about aspect of biomimetic restorative dentistry.
00:00:55.572 --> 00:01:08.352
Obviously, Doctor Pascal Magne has been very prominent in promoting that concept, but the history of immediate dentin sealing goes way back, and the early origins of that are important.
00:01:08.652 --> 00:01:11.621
They come from two different universities.
00:01:16.659 --> 00:01:32.742
One university is Tokyo Medical and Dental University that we've talked about in the past, and we've talked about how important it was to develop the caries detecting dye and the techniques of understanding the different layers of dentin that are affected by decay.
00:01:32.742 --> 00:01:42.218
The most common pathology and so Fusayama’s position as the father of adhesive dentistry, also becomes the father of biomimetic dentistry.
00:01:42.218 --> 00:01:46.290
Because without adhesive dentistry, we can’t have biomimetic dentistry.
00:01:46.322 --> 00:02:06.742
But beyond that, without caries removal end point consistency, we can’t have predictable adhesive hybrid layers established and so after we’ve talked about caries detecting dye caries diagnosis and treatment, selective caries removal versus total caries removal to protect the pulp.
00:02:07.076 --> 00:02:13.349
And then the last two lectures we’ve talked about cracks and gaps and how they allow infection.
00:02:13.716 --> 00:02:18.055
The cracks and gaps are a pathology that endanger the pulp.
00:02:18.355 --> 00:02:25.194
Decay, obviously, is a pathology driven by the presence of bacteria in the decay process.
00:02:25.495 --> 00:02:38.141
But once we've treated those two pathologies with selective removal so that the pulp can heal, now we're starting the rebuilding of a biomimetic restoration.
00:02:38.408 --> 00:02:46.083
My son Davey, who's been teaching with me for 12 years, coined the phrase that the six lessons approach is a bottom to top approach.
00:02:46.382 --> 00:02:48.651
Most dentists like to look at pretty tops.
00:02:49.853 --> 00:03:21.951
It's a human thing to look for beauty, but if you're looking at the top of the tooth, you're not really understanding the unique characteristics of a tooth that allows it to distribute forces of occlusion throughout the whole tooth, and that connection of the whole two side to side, front to back up the bottom can only be accomplished when a strong hybrid layer is established, connecting the tooth to the materials that are restoring the missing parts of the tooth that have been destroyed through pathology.
00:03:21.951 --> 00:03:28.925
And so when Fusayama started to investigate bonding to dentin the interaction was not understood.
00:03:28.925 --> 00:03:38.302
But soon it was connected with early bonds to enamel that were understood and had been established in the mid 50s by Michael Buonocore.
00:03:38.502 --> 00:04:03.560
Michael Buonocore was using a bonding system called sevreton and sevreton had the ability to polymerize, and these polymerization the molecules that polymerize with etched enamel that was born, of course, huge breakthrough to surface condition the enamel so that there were micro porosity that could be engaged by the polymerize in composite.
00:04:03.860 --> 00:04:10.300
The polymerization composite was actually not a composite, it was a polymerization poly methyl methacrylate.
00:04:10.300 --> 00:04:12.569
So poly methyl methacrylate works great.
00:04:12.569 --> 00:04:14.204
It has a lot of shrinkage.
00:04:14.204 --> 00:04:17.874
We've been using it since the 30s very effectively.
00:04:17.874 --> 00:04:22.512
And epoxies and various materials that we would call plastics.
00:04:22.778 --> 00:04:29.653
But the shrinking of plastics, if they're done outside of a situation, can be controlled.
00:04:30.286 --> 00:04:41.932
If you're molding something and you have a mold and you say, okay, we're going to have 7% shrinkage is small, then after the shrinkage has happened in the plastic, you look at it and say, that's the size that we have.
00:04:42.199 --> 00:04:48.138
So that shrinkage that happens inside of a mold is not a negative thing.
00:04:48.538 --> 00:04:52.975
Because now you have the item that can be used with the shape that it has.
00:04:53.242 --> 00:04:55.245
It's a very different situation.
00:04:55.245 --> 00:05:01.752
When we start polymerizing materials in what we call in situ in the actual body.
00:05:01.985 --> 00:05:15.165
And so that shrinkage that happens inside the hybrid layer of enamel, it wasn't really appreciated because there was a high connection with enamel, because it was a dry material.
00:05:15.165 --> 00:05:58.542
But from the mid 50s until 1975, for 20 years, bonding to dentin was not in any way predictable or consistent until a new chemistry was established and that new chemistry was established at Tokyo Medical and Dental University, and that chemistry took a molecule and that molecule, instead of having two ends that were hydrophobic, which is the case with all epoxies and all poly methyl methacrylate polymerizations those molecules now were divided into an end that had a hydrophilic molecule attached to it.
00:05:58.842 --> 00:06:08.451
And so the hydrophobic, in which most plastic engineers are expert at this is now called a bipolar molecule.
00:06:08.884 --> 00:06:12.756
So the bipolar molecule the first one that was made was very short.
00:06:13.023 --> 00:06:19.062
It had an end that was hydrophilic, which is called phenyl end and then an end.
00:06:19.062 --> 00:06:21.431
That was the methacrylate end.
00:06:21.431 --> 00:06:51.728
And that poly was called phenyl-p molecule was first introduced from a team of scientists who were working at Tokyo Medical and Dental University from a company called Kuraray, Kurashiki Rayon, Kuraray They had chemists that knew about polymerization molecules, and they knew in this chemistry that they had a very difficult challenge to bond to dentin, the bond to detonate.
00:06:51.728 --> 00:06:54.730
We referred to earlier from this material.
00:06:54.831 --> 00:07:09.346
They came from a Swiss chemist named Oskar Hager and then made into a dental filling material in England had terrible results because although it could go from a soft to a hard state, that's called polymerization.
00:07:09.346 --> 00:07:13.617
It had the shrinkage of a polymer of a factor rate, which is about 778%.
00:07:13.750 --> 00:07:15.651
And so this created a gap.
00:07:15.651 --> 00:07:33.770
But the bond to dentin which we referred to in the earlier lectures, which was an unintended consequence, there was a nitric acid contaminant in the synthesized molecule of the GPDM which was the molecule they were polymerized in, which came from the epoxy.
00:07:33.770 --> 00:07:35.739
That history we've referred to it.
00:07:35.739 --> 00:07:47.217
It was a failure that didn't work as a dental restorative material And so when it was revisited by the Japanese, they had a very important insight.
00:07:47.217 --> 00:07:52.288
And that insight was that in dentin we have to work with the water.
00:07:52.288 --> 00:07:54.424
20% of dentin is water.
00:07:54.424 --> 00:07:55.391
Now, the 20%.
00:07:55.391 --> 00:08:03.466
This water is also integrated into a matrix that is built by collagen that's encrusted by hydroxyapatite.
00:08:03.567 --> 00:08:05.134
So we have three elements.
00:08:05.134 --> 00:08:08.572
There are moist, one stiff and one's flexible.
00:08:08.805 --> 00:08:13.944
And so the chemists at Kuraray made this molecule phenyl P.
00:08:14.144 --> 00:08:21.251
And this was the first molecule that fusion was able to see on a flat surface at a bond to dentin.
00:08:21.550 --> 00:08:28.959
But he had to use a phosphoric acid to condition the dentin Just as the phosphoric acid had been used.
00:08:28.959 --> 00:08:37.766
It used in 1955 by Michael Buonocore to condition and makes the micro grooves into the enamel well.
00:08:37.833 --> 00:09:07.529
Fusayama when he saw this in a demonstrated even though the bond strengths were low in the four or six, maybe eight Megapascal range, he knew that it was an important breakthrough, but he always felt like this interaction of a positively charged end of a molecule and a negatively charged end of a molecule had something to do with the chemical interaction, and the chemical bonds that he believed were established could not be proved at that time.
00:09:07.764 --> 00:09:16.373
The type of bonding there's two types of bonding that we're talking about here would be an ionic bond and then a cohesive bond or a covalent bond.
00:09:16.373 --> 00:09:21.311
I should say covalent bond and ionic bond can give cohesive strength.
00:09:21.378 --> 00:09:26.615
A crystal, for example, is totally ionic bonding, and it has cohesive strength.
00:09:26.615 --> 00:09:29.519
It's usually brittle, like hydroxyapatite.
00:09:29.519 --> 00:09:45.534
But then the bonds that are covalent bonds, which are stronger, are also part of the depth and complex in the collagen, which has covalent bond in that holds the molecules of the protein of the collagen molecules together.
00:09:45.835 --> 00:09:58.914
So when this phenyl P was synthesized, they had the initial success and an initial insight, and it was investigated within four years of this synthesis.
00:09:58.914 --> 00:10:05.522
1978 to 1982, by another doctor, but not a doctor of dentistry.
00:10:05.522 --> 00:10:10.092
At TMDU, he was a chemist, so he had a PhD in chemistry.
00:10:10.092 --> 00:10:12.428
His name is Nobuo Nakabayashi.
00:10:12.428 --> 00:10:26.743
He passed away last year, but Nakabayashi started to synthesize other molecules and he also started to investigate with scanning electron microscopy and with transmission electron microscopy.
00:10:26.875 --> 00:10:35.185
These connections between the composite and the dentin And that was his life's work.
00:10:35.518 --> 00:10:50.466
My good friend Charlie Cox, who knew knuckleball as you well, spoke Japanese, but the brilliance of his chemistry could be reproduced, and his investigation through microscopy was exactly Charlie Cox's expertise.
00:10:50.834 --> 00:11:17.894
Charlie Cox, the histology, and Charlie Cox knew about preparations of specimens for light microscopy and for electron investigation on a scanning electron, and eventually transmission electron microscopy, and the connections between the materials in the body of the two became known and were named by Nakabayashi The hybrid layer because a hybrid not composite, not tooth.
00:11:17.894 --> 00:11:40.450
It was a combination of those two, so Nakabayashi naming of hybrid layer starts in 1982, but the investigation of that hybrid layer took years to get to the position where we understand exactly what's happening and that and understand in was given huge scientific validation or understanding.
00:11:40.450 --> 00:11:58.802
In 1993, ten years after the hybrid layer was established, Bart van Meerbeek did a four year PhD at Catholic University in Leuven, Belgium, investigating the hybrid layer in the interactions and the interactions with many dentin bonding systems.
00:11:59.067 --> 00:12:02.337
Here's a page from Van Meerbeek’s dissertation.
00:12:02.871 --> 00:12:13.249
This dissertation lists over 20 bonding systems, actually 30 bonding systems that were investigated by Bart Van Verbeek in 1993.
00:12:13.483 --> 00:12:17.620
Each of those 30 systems have proprietary chemistry.
00:12:17.787 --> 00:12:34.870
In other words, the recipes of the chemists of each of the different companies Biscoe, Bayer, Kuraray, Kulzer, DenMat, Coltene, Shofu, Johnson and Johnson, generic, Pentron, Kerr, SB Caulk Lee pharmaceuticals, 3M.
00:12:34.870 --> 00:12:48.350
Sun Medical, DMG Vivadent, denmat Tokoyama GC Kerr I mean these are companies who are making products and selling them to dentist to make dentistry better.
00:12:48.651 --> 00:12:56.893
And this idea of adhesion making dentistry better was the initial insight from Fusayama but they actually put it into practice.
00:12:57.125 --> 00:13:01.531
There are many concepts that have to be understood in this interaction.
00:13:01.563 --> 00:13:02.532
The hybrid layer.
00:13:02.532 --> 00:13:05.902
Van Meerbeek was able to break it down into three layers.
00:13:06.235 --> 00:13:09.239
He called them inter diffusion zones.
00:13:09.371 --> 00:13:14.711
You had a top middle and a bottom, not very sophisticated, but the bottom was closest.
00:13:14.711 --> 00:13:15.611
The dentin.
00:13:15.611 --> 00:13:18.147
The top is closest to the composite.
00:13:18.147 --> 00:13:27.289
But these three layers of these inter diffusionary zones add the ability to connect with these polymerize in molecules in different ways.
00:13:27.490 --> 00:13:34.029
The bottom zone was always the most important for its strength, but also the most contaminated with water.
00:13:34.029 --> 00:13:47.176
The middle zone a little of each, and then the outer zone was mostly composite, had high bond ability, but this connection of these three layers, to identify those and to know that this is where the strength came from.
00:13:47.442 --> 00:13:48.811
Huge insight.
00:13:48.811 --> 00:13:51.813
And Van Meerbeek, this is 2024.
00:13:51.813 --> 00:14:08.965
So for 30 years, Bart van Meerbeek has been collecting with his team data on the hybrid layer data on different bonding systems from different companies evaluating those systems and how they interact and form this connection with the tooth, the hybrid layer.
00:14:09.164 --> 00:14:16.004
In 2009, a fourth dimension of the three layers of the hybrid layer was added.
00:14:16.004 --> 00:14:30.620
That fourth dimension is called the acid base resistance zone, sometimes referred to as super dentin named by Tagami when he announced it at the International Association of Dental Research in Miami Beach.
00:14:30.919 --> 00:14:34.289
I was sitting next to Simone Deliperi at that meeting.
00:14:34.624 --> 00:14:54.409
400 dentists were listening to this breakthrough information, but this area that was below the hybrid layer, in other words, this was in dentin said that some molecules that had been introduced in 1989 was the first invention of this new molecule.
00:14:54.777 --> 00:15:05.989
They had the ability to like snakes going underground, getting into the dentin, and they could go in these little channels that were micro channels filled with this 20% of water.
00:15:06.254 --> 00:15:28.945
And then for one micron or even two microns below the hybrid layer, this acid base resistance zone, which the gummy called super dentin because they found out that once the polymerization of these four into diffusion in your layers was made, you could not dissolve this dentin that had been infiltrated through the hybridization process.
00:15:29.379 --> 00:15:41.057
But the molecule that achieve that was not phenyl P, the molecule that achieved that was in collaboration with the two organizations Kuraray and TMDU.
00:15:41.289 --> 00:16:00.909
The chemist was named Omura, and Omura had the ability to understand that well, if you're trying to separate water loving elements of the hybrid layer from water hating elements of the hybrid layer in this inter diffusionary zone, hydrophobic, hydrophilic.
00:16:01.344 --> 00:16:12.221
If you had longer molecules, then you could allow the water to come in and be encapsulate it by these molecules very easily.
00:16:12.855 --> 00:16:15.291
And so they made the molecule longer.
00:16:15.291 --> 00:16:19.829
And so it was actually about three times as long as the phenyl p.
00:16:20.529 --> 00:16:38.313
And this length of the molecule, which was called 10 MDP, allowed it to have interaction with water in this area in between the part of the molecule that didn't like water and the part of the molecule that liked water.
00:16:38.313 --> 00:16:50.659
And so it worked very well in this gooey area that's been polymerize and taken from a watery state to a dry state in the hybrid layer.
00:16:51.027 --> 00:16:53.796
But the thickness of that hybrid layer.
00:16:53.796 --> 00:17:03.306
Traditional hybrid layers were investigated and thought to be five microns thick, and they showed invagination of the composite resin into the tubules.
00:17:03.306 --> 00:17:07.242
And these little projections of the resin in the tubules were called tags.
00:17:07.442 --> 00:17:10.445
And they were thought to be very important as far as the strength.
00:17:10.445 --> 00:17:15.851
The longer the tags into the tubule, the more strength of your resin infiltration.
00:17:15.851 --> 00:17:17.854
Turned out that was totally an artifact.
00:17:17.854 --> 00:17:19.254
It wasn't true at all.
00:17:19.254 --> 00:17:27.163
And actually, Fusayama in his books in 1980 and 1993, I'm not sure there was in 1980s book, 1993.
00:17:27.163 --> 00:17:28.597
I know that it's there.
00:17:28.597 --> 00:17:40.609
Showed that in a hydrating pulp, you have a whole fluid that's been pumped regularly with the heartbeat, and that's preventing any infiltration of the resin into these tubes.
00:17:41.042 --> 00:17:43.913
Of course, it would be different in a non vital tooth.
00:17:43.913 --> 00:17:50.586
You can get a tag into an end, wrongly treated tooth, and all of the teeth that were being tested at that time were extracted.
00:17:50.586 --> 00:17:58.660
Teeth did not have pulps with vital fluid, and so the resin tags, you know, they were kind of looked sexy, but they didn't mean anything.
00:17:58.660 --> 00:18:22.117
But I can remember as I was a dentist trying to figure these things out in the 80s, getting more and more confused every year that things came out because these bonding system did not work, even though companies promised me that they were working in their body to then these were very, very weak and restorations required retention form, resistance form.
00:18:22.651 --> 00:18:29.958
All of the traditional mechanical retentive forms of the cavity were necessary to make these adhesive systems work.
00:18:29.958 --> 00:18:32.127
They weren't they weren't adhesive.
00:18:32.127 --> 00:18:48.910
As we start talking about this connection, and once we establish and this happens about 1998, 1997, where we actually have a dental bonding system that has a combination of phenyl P and 10 MDP, it's called liner bond two.
00:18:49.144 --> 00:18:55.417
And that system in in vitro tests is like triple the strength of other systems before.
00:18:55.817 --> 00:18:58.420
And there's many things that go into that.
00:18:58.420 --> 00:19:11.032
We talked a little bit earlier in a lecture about the Liner Bond Original System liner bond one, which was developed by Hosoda and Hosoda at the insight that we had to get rid of the smear layer.
00:19:11.266 --> 00:19:14.436
But then once we got rid of the smear layer, we had a collapse of the collagen.
00:19:14.436 --> 00:19:17.405
So we had to prime the college and to puff it up a little bit.
00:19:17.405 --> 00:19:32.320
And then we could use a moderately effective bonding system that did have ten MDP called photo bond, but the only way it really worked on a vital tooth is to immediately put a a, a layer of a flowable composite.
00:19:32.320 --> 00:19:38.426
And that flowable composite, was the protect liner f the first flowable composite in the world.
00:19:38.660 --> 00:19:41.596
Anyway, there were many steps in this liner bond system.
00:19:41.596 --> 00:19:51.840
The liner Bond two system was much simplified because it had an exclusive primer and bonding system that was based on this ten MDP.
00:19:52.274 --> 00:20:03.051
Other molecules in the primer like Hema, and other molecules in the hydrophobic end like Bis-GMA and Tegma Those are proprietary mixtures that each company has.
00:20:03.051 --> 00:20:16.965
But the companies that had monomers that weren't as good as the ten MDP or as polymerizable as the GPDM, which turned out to be another strong candidate for a gold standard bonding system.
00:20:17.198 --> 00:20:22.270
Other companies tried other molecules and they tried other combinations of conditioning acids.
00:20:22.270 --> 00:20:25.273
They tried other combinations of solvents.
00:20:25.540 --> 00:20:27.876
Acetone became very popular.
00:20:27.876 --> 00:20:29.244
Ethanol, water.
00:20:29.244 --> 00:20:42.490
All of these proprietary recipes have an effect on the hybrid layer establishment, and the hybrid layer establishment, once it's in place, becomes the first layer of connection.
00:20:42.791 --> 00:20:48.430
But that layer of connection has to be connected with the rest of the restoration.
00:20:48.430 --> 00:21:00.175
Well, in Japan, there were many investigators using these early systems and found that they did work and they were having success in vital teeth even on pulp exposure.
00:21:00.275 --> 00:21:03.378
Research was done by Kashiwada in 1991.
00:21:03.378 --> 00:21:09.551
Kashiwada did direct bulk caps on real people with these early bonding systems.
00:21:09.818 --> 00:21:14.322
And then we had a study in 1994 on an indirect technique.
00:21:14.456 --> 00:21:23.765
And in this indirect technique, we had, through Sato, an establishment of a superior result.
00:21:23.898 --> 00:21:30.038
This is a clinical trial using this idea of what we call now immediate and ceiling.
00:21:30.071 --> 00:21:31.740
It wasn't called that then.
00:21:31.740 --> 00:21:38.179
What it was called is using liner bond system as dentin and pulp protector in indirect restorations.
00:21:38.480 --> 00:21:41.950
So that's called immediate dentin sealing in 1994.
00:21:41.950 --> 00:21:55.330
But within two years, researchers at another outstanding research institution led by their director, who was named Peter Scharer at the University of Zurich, had another article published.
00:21:55.330 --> 00:22:02.203
And in that article, we had the ability to compare the results coming from Japan and the results coming from Europe.
00:22:02.370 --> 00:22:07.809
And the authors of this Christian Bertschinger was the lead author.
00:22:07.809 --> 00:22:15.850
Stefan Paul was the second Heinz Luthy, and then Peter Scharer is the final author, the one directing the research at University of Zurich.
00:22:15.850 --> 00:22:26.327
When they published this article in 1996, and then they followed up with the article that I first read that led me to understand that this was something very important.
00:22:26.694 --> 00:22:28.530
So this is 1997.
00:22:28.530 --> 00:22:38.840
So now we have actually a name for this idea of doing a bonding step initially at the preparation stage and then doing a bonding step at the cementation stage.
00:22:38.840 --> 00:22:46.481
Now they called it dual bonding, but they were trying to solve a problem that did not relate to the strength of the bonds.
00:22:46.848 --> 00:22:57.659
Their problem that they tried to solve with that paper was contamination of dentin by tamper resistant materials, which were almost always eugenol based.
00:22:57.759 --> 00:23:11.139
And so they knew that if they had eugenol, contamination, the polymerization of the GPDM molecule, or the ten MDP molecule or the molecule that was synthesized by Biscoe in all bond two was successful.
00:23:11.139 --> 00:23:11.840
Molecule.
00:23:11.840 --> 00:23:21.950
Also, they understood that this eugenol interfered with the chemical reaction, and so the polymerization was weakened or even completely negated by eugenol.
00:23:22.116 --> 00:23:38.867
So their idea was how about if we sealed the dentin Dentin doesn't get contaminated by eugenol, and then we can put the temporary restoration in, and then it's easier to clean off this eugenol, because now we have this adhesive layer that's been polymerized that protects this from the contamination.
00:23:38.867 --> 00:23:40.869
That was the problem they were solving.
00:23:40.869 --> 00:23:45.607
And they had better success because now they had bonds that were bonding to the dentin.
00:23:45.607 --> 00:23:54.817
And the sensitivity that was endemic on direct and indirect restorations was being solved by using these better bonding systems in the 90s.
00:23:55.016 --> 00:24:02.257
But the strength of the bonding systems that were coming out of these earlier Kashiwada or Sato from Japan.
00:24:02.490 --> 00:24:06.761
Paul and Scharer and Bertschinger out of Switzerland.
00:24:07.096 --> 00:24:15.637
The bond strengths were still low and so all of the details of the chemistry in many systems were not being progressive.
00:24:15.637 --> 00:24:23.945
But when the who are a company in 1997 came out with this line or bond two system, it was considered a self etch system.
00:24:23.945 --> 00:24:40.094
And so no phosphoric acid conditioning, removal of the smear layer was needed to get higher bond strength, and the higher bond strength they got were around 20 mega pascals, which were twice as strong or three times as strong as the early systems.
00:24:40.461 --> 00:24:45.300
that the Van Meerbeek tested in 1993 that were developed in the 80s.
00:24:45.567 --> 00:25:06.921
And so this self etching system now, it was a simplification, but it also didn't give us the exact numbers that they were using to have these successful in vitro clinical trials that they ran from 1997 to 2007, saying that these restorations are functioning successfully.
00:25:06.921 --> 00:25:10.992
They're not showing signs of leakage or decay fracture.
00:25:11.259 --> 00:25:23.271
So this in-vivo study that was done by Yasuko Momoi and Naotake Akimoto ten year in vivo study takes a lot of time, a lot of effort, a lot of resources there.
00:25:23.471 --> 00:25:28.810
When that came out and published in 2007, it changed the world for people who are paying attention.
00:25:28.810 --> 00:25:38.019
But we also had to understand how a direct restoration or an indirect restoration differ, and how the structure of the tooth differs.
00:25:38.252 --> 00:25:56.337
And so these concepts started to be followed in the 90s, and then during the 2000s, which is now still or 2024, but in the early 2000, technologies to make indirect restorations more chair side friendly.
00:25:56.337 --> 00:26:10.785
We call that technique a semi direct technique, which was first introduced with chair side inlays on lays at Creighton University, but did not work even on the polymerization of the material, was done outside of the restoration, so that shrinkage didn't affect it.
00:26:10.985 --> 00:26:23.631
There was a problem when they tried to bond that restoration that had no shrinkage, but they had not dealt with the idea that in the hybrid layer itself, there is shrinkage in the hybrid layer.
00:26:23.631 --> 00:26:28.136
That itself there is a polymerization that has to be maximized.
00:26:28.136 --> 00:26:31.372
It has to be used to strengthen the hybrid layer.
00:26:31.539 --> 00:26:37.945
And so when Dietschi and Spreafico published their book in 97, they didn't have this figured out.
00:26:37.945 --> 00:26:45.721
They had the idea of a semi direct restoration not causing polymerization shrinkage because it's polymerized in outside the cavity.
00:26:45.721 --> 00:26:58.866
But then they didn't have figured out that they had to hybridize the dentin or what Pascal likes to call immediate dentin sealing, and we all call it immediate dentin sealing now but Doug Terry used to call it pre hybridization.
00:26:58.866 --> 00:27:03.838
Bill Liebenberg also called that pre hybridization in 1999.
00:27:03.838 --> 00:27:16.951
But the idea of in an indirect restoration or a semi direct nearside restoration to have a maximum interaction and bond strength, you have to hybridize the hybrid layer first and then wait a period of time.
00:27:17.285 --> 00:27:24.625
It may be 30 minutes to make the steric restoration, or maybe two weeks if the lab is making your indirect restoration.
00:27:24.625 --> 00:27:47.648
But the idea of this dual bonding means that there is a separation in time between the hybridization of the dentin and the cementation and that was a critical insight that came from the University of Zurich and Peter Scharer when he published these two papers Stefan Paul, when he published coauthor on those papers had that insight.
00:27:47.648 --> 00:27:49.751
But how does that insight get out?
00:27:49.751 --> 00:27:52.987
How does it spread from one university to another university?
00:27:53.154 --> 00:27:56.724
Well, if you're in Switzerland, it's easier than if you're in California.
00:27:56.724 --> 00:28:12.306
But eventually Stefan Paul left University of Zurich and went to UCLA in California, where I grew up, Los Angeles, and he was at the University of California, Los Angeles, same time that Charlie Cox was at the University of California at Los Angeles.
00:28:12.306 --> 00:28:33.761
And when Charlie Cox understood and Stefan Paul understood, and these concept of immediate dentin sealing before a restoration was bonded, the tooth had to do with the polymerization of the cement and the polymerization of the cement is going to move because all polymerization materials move.
00:28:34.163 --> 00:28:39.467
In other words, whenever you have shrinkage, if there's no walls, the shrinkage goes towards the center.
00:28:39.600 --> 00:28:43.137
If it's bonded towards one wall, then the shrinkage can go here.
00:28:43.337 --> 00:28:57.852
But if there's two walls and you have a layer of cement shrinkage, the cement has to decide am I going to stay where I am and have equal movement towards both walls, or am I going to move towards one wall at the expense of one wall?
00:28:58.052 --> 00:29:01.823
And what that is called is the hierarchy of bondability.
00:29:02.056 --> 00:29:17.071
If you have one wall that's drier and more acceptable to polymerization immediately, versus one wall that's moist and flexible and has a little bit of slipperiness, then the shrinkage is going to move towards the dry wall, which would be the restoration.
00:29:17.238 --> 00:29:20.975
And that cement will pull away from the dentin surface.
00:29:21.375 --> 00:29:27.115
And so the concept of hierarchy bond ability was developed by myself.
00:29:27.215 --> 00:29:33.621
And that was trying to solve the question of why this dual bonding system worked.
00:29:33.988 --> 00:29:41.295
And the other systems that were used, but not from the University of Zurich, didn't work well.
00:29:41.562 --> 00:29:52.573
The hierarchy of bondability can be applied to why does bonding to carious dentin work, or why it doesn't work if it's connected with a layer of composite?
00:29:52.573 --> 00:29:57.879
That's too thick, too soon in the polymerization of the hybrid layer.
00:29:58.145 --> 00:30:06.888
And so the hierarchy vulnerability is overcome using the dual bonding technique, which we now call the immediate dentin sealing technique.
00:30:07.288 --> 00:30:13.294
It works because time is put into the restorative process.
00:30:13.561 --> 00:30:21.669
And that time, if it allows the hybrid layer to mature all of a sudden, negates this hierarchy bond ability.
00:30:22.003 --> 00:30:33.714
In other words, if this is an immediate, then seal and resin coated surface, and this is the integral surface of a restoration composite or a silanized ceramic.
00:30:33.714 --> 00:30:37.451
These are both bonded at the same rate.
00:30:37.718 --> 00:30:39.221
They're both dry. Now.
00:30:39.221 --> 00:30:45.059
The hierarchy of bondability has been neutralized by immediate dentin sealing and resin coating.
00:30:45.059 --> 00:30:49.163
And so now we only have to worry about moving through shrinkage.
00:30:49.163 --> 00:30:55.336
These two surfaces closer together, which can happen, is usually a good thing if we have a lower C factor.
00:30:55.503 --> 00:30:59.607
But the other thing that can happen is you can have a strain in a tooth.
00:30:59.607 --> 00:31:09.350
And so in a large restoration which you have a thin cusp onlaying, a thin cusp can allow that movement to move in one direction instead of moving in two directions.
00:31:09.350 --> 00:31:28.869
But again, if the hierarchy of bondability of the whole surface of the cavity is neutralized, so that now all surfaces are basically bonding at the same rate as enamel bonds, then you can only have a slight movement, perhaps, of your two structure or a slight derangement of your polymerize in cement layer.
00:31:28.869 --> 00:31:34.108
But these are all small stresses compared to the stress of the hybrid layer.
00:31:34.108 --> 00:31:41.048
If it's early in the formation, it's detrimental to the tune, usually of 80% of the strength.
00:31:41.048 --> 00:31:49.824
The hybrid layer is lost in a bulk fill restoration, for example, and so immediate dentin sealing that comes from Japan and comes from Europe.
00:31:49.824 --> 00:31:57.465
From TMDU and from University of Zurich are the breakthrough that allow these CEREC restorations, for example, to be effective.
00:31:57.465 --> 00:32:02.203
And once the dual bonding technique was applied with CEREC you had a winning combination.
00:32:02.336 --> 00:32:12.413
The hierarchy of bondability was neutralized, and with the CEREC you had the polymerization which is needed, which we call the decoupling with time step.
00:32:12.413 --> 00:32:15.750
At about 30 minutes, it took about 30 minutes to design and mill.
00:32:16.050 --> 00:32:42.410
All of these add up, and they build upon the idea of getting an ideal caries removal point so that you have a maximization of the bond strength of the surface that you're trying to bond your restoration to, to this cumulative understanding of adhesive systems, the hybrid layer polymerization dynamics, polymerization shrinkage, strain on the tooth, amount of strength that we get from using this.
00:32:42.610 --> 00:32:47.815
All this research kind of culminated 2005, in a paper that Pascal Magne wrote.
00:32:47.982 --> 00:32:54.088
And in that paper, he had numbers that nobody else had been able to to come up with.
00:32:54.188 --> 00:33:02.096
And those numbers in this paper, this is 2005, published in the Journal of Prosthetic Dentistry, gave us exact numbers.
00:33:02.229 --> 00:33:23.918
If you do immediate dentin sealing and bond a indirect restoration to that surface versus an indirect restoration bonded and cemented at the same time, which is called delayed dentin sealing IDS versus delayed dentin sealing showed an increase of bond strength with IDS 400%.
00:33:23.984 --> 00:33:41.635
So we're getting bond strengths instead of in the 11 range in the 50 and 60 range, and the 50 and 60 range is the number we love, because the tensile strength of the DEJ is 51.1, as measured in 2000 by Urabe and the other members of the team TMDU.
00:33:42.069 --> 00:33:44.038
Anyway, a lot to think about.
00:33:44.038 --> 00:33:45.473
Till next time, stay bonded.
