How Does Air Abrasion Affect a Restoration?

Air abrasion functions as a conditioning step when bonding, which means it prepares the dentin or composite molecules for bonding. Dr. David Alleman discusses the progression of bonding systems for dentin adhesion and how this conditioning step evolved along with the bonding system molecules. The latest studies from researchers independent from the bonding system manufacturers show that air abrasion increases bond strengths to a level that mimics the strength at which a natural tooth is connected to itself (30-50 MPa). This conditioning technique is what brings dentin bond strengths into the biomimetic range, maximizing bond strength and the longevity of the restoration.

Articles referenced in this episode:

• Urabe I, Nakajima S, Sano H, Tagami J. Physical properties of the dentin-enamel junction region. Am J Dent. 2000 Jun;13(3):129-35.

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Transcript

0:33

it's our pleasure. In episode seven of season two to talk about a subject that, shouldn't be controversial, but it is a little bit misunderstood. And that is. How does air abrasion affect a restoration? Again, in the six lessons approach, we have analysis of the bottom part of the restoration and the top part of the restoration. The middle has connections. So we're connected bottom to top. And it's a bottom to top restorative process. So there's two times when we in our protocols use air abrasion. And we do them with specific purposes based on specific science. The first is creation of the hybrid layer. Now when we talk in six lessons about the creation of the hybrid layer, we're trying to set a particular foundation that you understand that a hybrid layer which is our logo, we have four layers in our logo because there are four zones in the hybrid layer. Using a mild, self-etching, bonding system. Now understanding that phrase a mild self-etching bonding system that has been developed and published for decades now. But interestingly enough, the idea of a self etching bonding system was an unintended consequence. Now, in science, there are usually surprises and hopefully the surprises, don't have catastrophic. My favorite, a movie of the last year was Oppenheimer, because right before they exploded the first atomic bomb, General Groves, who's supervising for the government, the project, came to realize that there was a slight possibility that once you started a chain reaction, everything would become part of the chain reaction, and you'd have a destruction of the known world that we have. That was just a minor piece of science thrown out by, one of the researchers at the Los Alamos. And General Groves was like, how close, you know, to zero is that, Oppenheimer said something like, well, it's very close. You know, it is like, but it's not zero. Okay. So in science, when you do things, it's not like everything is always understood. And when we developed adhesive dentistry or the heath to dentistry principles were being developed, it had to become understood little by little by little. And, it starts in 1951 when a chemist from Switzerland who really didn't know anything about dentistry, came to market with a product that bonded to dentin And that was the claim. 1951 Sevreton Oscar Hager made the claim. They sold it to dentists. Only one problem. It didn't work. False advertising, perhaps, but in reality, he had some tests where on flat dentin surfaces, this certain, polymerized and it stuck to the dentin. And so that was the first step. And then they decided to put a white plastic material called poly methyl methacrylate on top of that, which had a shrinkage of about 8%. And so if you put it in a tooth and you had that much shrinkage, all of a sudden you get no bond, the first hour. And, it was a terrible disaster. But what can you say? That's history. Well, the product, GDM was the monomer had a polymerized monomer that was very good, polymerized with a chemical cure reaction. And then, when the, Revitalization of adhesive dentistry came after the Japanese Products became became, successful in the early 80s. This was 30 years after the Sevreton Disaster. Kerr a large manufacturer of dental products, hired a young chemist named Al Kobashigawa and Al Kobashigawa, had a master's degree from Cal State. La very bright chemist, and he was given the task to create a bonding system for Kerr that could compete, successfully with the Kuraray and also the all bond products that were coming out of Bisco. Those were the two leaders anyway. So Al you know, he didn't know anything about dentistry, knew about chemistry, but he knew the patents were kind of important because they protected some proprietary information. And the proprietary information. When you did a patent search on dental adhesives, came up with this patent application, 1951 1950 by Oscar Hager. And he saw this molecule, GPDM And, this glycerol phosphate dye methacrylate. You know, Al speaks chemistry and he knew that he could make it. And he, started to, experiment with it. And then he started to talk to some of the people, in Japan. And the people in Japan and Korea are great chemists, most of whom have PhDs. But, you know, if you have a master's degree in chemistry, you can talk to language plus he Japanese. So Al Kobashigawa speaking probably in English, not Japanese, with other researchers, found out that. The original GPDM molecule that polymerize and bonded to that. And when the Japanese made the molecule to try to reverse engineer this vulnerable product, to dentin that Hager claim bond to the dentin. But when the Japanese synthesized the molecule and polymerized it on top of dentin, it didn't bond to dentin So what is a is a well, you know, they were just lying or whatever. I mean but they they figured that there was something happening that they didn't understand. And, they turned out that they were able to, I think, maybe get some inside information. I mean, it's, you know, this is, 1970s, 1950s, 20 years later. But chemists talking to chemists found out that the synthesis of the GPDM by the, British Asians and Swiss chemists had a contamination of nitric acid in the synthesis. The Japanese, when they synthesized that, did not have the contamination. Nitric acid. So what that meant is that there was an acidic part of this early bonding system that actually changed the design and allowed the GPDM molecule to adhere to it, but when the Japanese did it, their purification was so good of the GPDM molecule that without the nitric acid, it did not bond. Now, this is a history that nobody knows, nobody talks about, hasn't been written about. It's all proprietary information company against company. You know, you know, Al is a good guy, and, The product that they came up with took this molecule from Oscar Hager in 1951. And the technique of taking away the smear layer, the Fusayama innovated in 1978, which was acid etching with phosphoric acid. And he got that idea from bona cause using modification of phosphoric acid on enamel to allow this seven molecule to polymerize to enamel. And it did, but without the phosphoric acid etching bond, a court could not make the. The adhesion happen with this product. I mean, this is your 1950s and then you go 1970s. They've got different approaches, different molecules. The first bonding molecule that Korea put to market was called phenol pee. It was quite acidic. But again that acidic molecule phenol pee was put in to polymerize in a moist environment. So you needed to have an acidic end and a polymerize end which is the methacrylate end. Hydrophobic and hydrophilic And that was the way to mix and get integrated before the polymerization into this moist dentin substrate. Oh my goodness. Well, the bond strings with acid etching increased dramatically because the smear layer was removed. But the bond shrinks were still in the ten Mega Pascal range instead of the 4 to 6. Well, that's big deal, but that's still not anywhere close to the connectivity of a tooth to itself. So if you have a bond that's in the five and six range and it's bonded, but the actual tooth is connected at ten times that strength, you know, it's not like a tooth. It's not like life. It's not biomimetic when the progress started to be seriously undertaken by curare in conjunction with TMDU the innovation, phosphoric acid was like accepted. All of the products in the 70s had this conditioning step. So the removal of the smear layer by phosphoric acid, that's called conditioning. If you didn't condition by removing the smear layer, then your bond strings would be 4 to 6 rather than 10 to 12. But they were still seeking for a higher bond strength. And polymerized molecules are not easily made. But chemists at Kuraray came up tomorrow is the famous chemist who is totally unknown because they kept his name secret. Why, I don't know, but Umora working for Kuraray came up with the molecule ten MDP, which is a much longer molecule. Then the phenyl P longer also than GDM. Now the length or size of the molecule becomes important because, what's called stoichiochemistry. In other words, sometimes molecules don't fit because they're too wide. So skinny molecules sometimes have a big advantage if they're sneaking into small areas. And this ten MDP was like that long skinny ten carbons on its, chain that separated the methacrylate in from the phosphoric acid in the hydrophilic end, which is phosphoric acid, and the hydrophobic end, which is the methacrylate. Anyway. So Umora comes up with this new molecule. They start testing it and it's twice as good as phenyl p But because they have this experience with phenyl P they're a little loyal to it. Their first projects when they use it in MDP then they made another project. They say, well maybe these smaller molecules work better is they're integrating into parts. It was a good idea. And so they made products that have half phenyl P and half ten MDP. And this product that came out was the game changer. And that combination of phenyl P and ten MDP in the primer and in the adhesive, was called liner bond two and liner bond one had ten MDP, you know, dental bonding system. But it was a dual cure with a very thin adhesive layer. And it was a two bottle, one bottle system called Photo Bond. The thickness of the adhesive layer is a problem. If it's too thin, it doesn't polymerize because of air activation and transformation coming from underneath thins out that adhesive layer and photo bond had this problem. It was a great bond to enamel and one liner bond one came out. It was touted as both a dentin and an enamel bond, but it had five steps. It had a conditioning step with an acid that was a little less aggressive than phosphoric acid. That's a good idea. And that was called calcium citrate or a CA conditioning solution. But then to overcome the problem of removing too much hydroxyapatite, which caused the collapse of the collagen, if it was dried, then they had a primer. So you get the conditioner acid, weaker acid, and then they had a primer which is called SA primer, which helps fluff up the collagen, separate the college and fibrils so they could be infiltrated by this photo bond. But the photo bond again was too thin. It had its layer. And so that didn't work well on dentin because we had transmutation or inhibition. You put the light on it, you still had problems. Sensitivity. And then they came up with a very important product in that liner bond system, which was called Protect Liner F, which was the first floral composite in the world. And so the liner bond system, comes out in 1989, in Japan, 1992 In United States. And it worked on both enamel and dentin. But it had these five steps. And so it's a little complicated. And my first mentor, Ray Bertolotti, took it upon himself to simplify that and not use as a primer, and then to use the bond floor book composite that his company had made, which wasn't as good as the global composite that Kuraray made. And there were just a lot of a lot of confusion. He also used phosphoric acid, again, because he thought that it was pretty cool that you could make your own phosphoric acid and make it for cheap rather than expensive phosphoric acid that were coming from other manufacturers. I mean, Ray Bertolotti he had a vested interest to use. On the company. Danville. But all of this confusion that when I'm first learning adhesive dentistry is confusing. And if you're listening to this. Podcast and you're gonna listen to it again, listen to it again and write it down, hey, feel free. I'm trying to make your life easier now. In reality, are you ever going to need to know or use Liner Bond one? No. How about a liner bond two no, but Liner Bond two that exclusively, eliminated the removal of hydroxyapatite. Had that because in experimentation, when they're transitioning from the liner bond systems to this liner bond two or the liner bond one system and the Clearfil F1 and F2 systems, They did an experiment and the control was we get this bond strength of about 25 mega pascals. With acid etching. Well, let's see if we had no acid that you they did understand that the ten MDP molecule had an acidic. Effect. And so they tried it without acid etching just using the acidic. The mild acidic effect of the ten MDP molecules. And they found out they actually had higher bond strength. Without phosphoric acid. So when they're coming out with this new liner bond two system is like they eliminate the acidic conditioning. Wow. It's a big step, got to make up the story. And the story is the monomers are integrating in with the smear layer so it doesn't need conditioning because of this magic monomer. And the bond strings, that they get onto dentin are in the high 20s, low 30s. Sometimes a little bit higher. Actually there's one test they had, 42, I believe. But it showed that modifying the recipe of your bonding system modifies the strength, which is related to how the hybrid is hybrid layer is formed. Okay. So then this kind of becomes the gold standard. And then a couple of years later, SE bond, which eliminated totally the phenol p. That was the step for the brought that into now the 40s. So with the lighter bond system is getting the 30s now you eliminate phenyl P only use ten MDP and you don't have a conditioning step with acid. Now they're getting 40s and above. So SE bond becomes the gold standard. For the 20 years that it was under patent, it was the gold standard. And that patent on the MDP molecule ten MDP molecule kept the competition away for almost two decades. But then as soon as the patent expired, other products that use ten MDP because it's known in the science that it's the the superior molecule to any others. as it goes out, the starts to get tested. So this is 1998, 1999, 2000, 2001 to and then 2003 Bart van Meerbeek, who is the premier tester who's for ten years he's been at Catholic University in Belgium. He compares Optibond FL which is now the gold standard with the GDM and the phosphoric acid conditioning, a three step total edge technique. And then he compares it with. This up and coming gold standard SE bond. And he varies the conditioning steps. So with no conditioning which is the core recommendation. It was an innovation a breakthrough in 1993 liner bond two came in 1993. In the United States, 1996. But in 2003, van Meerbeek tries it with the manufacturer's recommendation, and he gets a bond strength of 36. And that's about what everybody else was getting, which. For the time when Liner Bond two was created, it was a huge breakthrough. But again, it had this mixture of phenyl P and tan MDP. So when they eliminated it, now we're getting higher bond strength. We're going into 37 instead of 27. But then Van Meerbeek has the good idea of using a technology that was introduced in the mid 80s and investigated by a very important investigator in London named Alan Boyd, and this was an abrasion. In the United States, air abrasion had been used, early on by SS White Company to prepare preparations that didn't really if the preparation had any size, it really wasn't a good idea. But the idea of drill is, preparation. Doctor Black from Texas, had this innovation and it was used, developed. Now it's still used in minimally invasive dentistry. Tim Rainey is kind of the father of that. But when Van Meerbeek used the air abrasion to test bond strength, he found out that just like Allen Boyd had said in 85, when you air braid or he called it air polishing, you are removing most of the smear layer which is just your chopped up dentin from your preparation with your burrs. And the smear layer interfered with the infiltration of early bonding systems in the 80s. Still did the same thing when is being tested 20 years later. But the interesting thing now is that the evolution of the dental bonding system now shows that you can go from 37 mega pascals to 56 mega pascals. but you have to use that conditioning step of air abrasion. It also has the advantage of stopping any fluid coming out of dental tubules by putting the smear layer that's on top of the orifice of the dental tubule and plugging in it, it compacts it into the tubule. So you have a dry bonding field. But all of the inter tubular dentin is exposed and receives the primer much better, maybe 30% better and higher development of the hybrid layer. And you get to these numbers that are 56 where now we're talking turkey because, you know, 56 is greater than the connection of enamel to then 2000. The connection of the enamel to dentin was established by Urabe and the team at of TMDU. Sano was part of that project. Tagami part of the investigation. Nakajima I mean, you know, all stars telling us enamel to dentin, 50 mega pascals And now if you use this gold standard bonding system, but now in a better way by conditioning, meaning removing the smear layer in the critical areas and keeping the smear layer in the other critical areas, it can help keep the bonding field dry so the primers aren't as diluted. Then all of a sudden you got these numbers 56. Wow. And so you would think when that revelation came out that everybody at the Kuraray company would be like buying stock in air abrasion companies if you understand a biomimetic approach, the advantages of a self etching system are maximized when air abrasion is used. And so it's something that we've always used all of our long term successes, 20 and now going into the third decade of service are all based on air abrasion technology. To condition the dentin. That means remove the smear layers into tubular lee and compact the smart smear layer. The smear plugs that are in the tubes. All right. So that's an abrasion for the bottom. Now how about air abrasion for the top. Connecting the enamel replacement to the dent replacement. The dentin replacement we call that the bio base. It's composites direct composite placement. If you don't use air abrasion, the numbers that you will get are around 25 mega pascals. There are 25. Mega pascals is not nothing. You will not have many debonds of your enamel connection to your dentin If you use only polishing with pumice rather than air abrasion. But you know I am a sick man. I'm trying for perfection. I'm trying to make no failures, would make me the happiest and the closer we get to know failures, the better. But if you have a demand of your enamel replacement to your dentin because your bond is 25 mega pascals, it just means that it wasn't strong enough to resist the fatiguing of chewing, you know, a million times a year. And occasionally a natural tooth will have a fracture of the dentin, off of, the enamel. Enamel off of the dent. Okay, so that's kind of biomimetic, but when these numbers are lower and I'm looking at them, I'm going, well, we got this research team in Denmark that just showed if you used air abrasion, that you could get those into the 30s very easily. This is an early paper published like 1998, 2000. Putsfield. That's a nice name. And Asmussen, showed that in Putsfield Asmussen, you know, said. Yeah, you just use air abrasion and all of a sudden you're accessing more of the, polymerize monomers that are in this direct composite. So there idea was how to make a composite or repair. But I'm taking these ideas from the composite repair techniques into the cementation of our enamel replacement into the bio base. And so the idea is that in composite when you put the light on it, the polymerization is going to be about 6,065% of the monomers are going to now be into polymers. But there's little islands of monomers that never get reacted through a free radical connection. Those are still accessible. But if you have a flat surface and you do air abrasion, all of a sudden you're you're doubling the surface area. So you're increasing the accessibility to the monomers. And that's why the difference between 35 with no abrasion and 56 with an abrasion, that is like you also in the hybrid layer we're accessing, and not only removing the smear layer, but you're actually accessing or making a better surface area of the entire tubular dent. And so you have more access to hydroxyapatite. Same thing on your bio base. You're having more access to the uncured monomers and those through the fusion reaction. Once the heated composite and the uncured adhesive that wets the surface after abrasion, and then the heated composite, and then the uncured adhesive on the the surface of your onlay once they're squished together at about 200 microns thickness, you put the lid on it and there's the fusion. The reaction of the heated composite is going two directions. It's diffusing into the surface area that's been increased on your bio base, and it's diffusing into the entangle surface of your enamel replacement. And all of those are polymerized at the same time. In your final cementation, like your step. And so then you get about 40 mega particles. And so that number was established. In the 2012, something like that. And so we, we now have a, underlay that has a cohesive strength in the 40s. We have the layer of the cementation that's in the 40s. We have the dentin replacement in the 40. There's no weak link there. The only place we really have a weak link that's not in that 30 to 50 Mega Pascal range is at the resin coating level, where we use stress reduce with ribbon to protect the developing hybrid layer on areas where there is residual decay that has been left after killing the bacteria in that residual decay. And that allows us to have a hybrid layer without taking the risk of exposing the pulp. And that's been our our protocol, our strategy. And, you know, millions of restorations are around the world doing this. And this is the approach that the six lessons, take. So they're abrasion for highest bonds in a hybrid layer or abrasion for the highest bonds, and the connection of enamel to the dentin and if we did have, over the years, some type of traumatic, force or occlusal forces accumulating, then we have a built in safe strategy or a fail safe strategy, what we call a secure bond strategy. Using that in the first millimeter of the dental replacement in our central stop zone around the pulp, a fiber placement to, protect that in the case that we never did have a failure of the dentin. Replacements only happen once. We have a case of that in the in the PowerPoint. Only trained, doctors, worked very well. But it's only happened once in 20 years where we've had a fracture of the enamel. Go to the fracture of the den and stop at the, central stop zone with the Ribbond placement. So if it never happens, that's even better. You know, you want all your teeth to not break. Unfortunately, some teeth without any decay, without any restorations. Still, under the years of of occlusal forces, have some, some failures. So here we are. We're in a imperfect world, but we're trying to make it as good as possible. So with that, we'll just sign off till our next lecture on six lesson podcasts. Get bonded, stay bonded.