So the first podcast we talked a little bit about early mentors and how getting bibliographies from my early mentors like Ray Bertolotti and John Kois helped me to understand that the science was available, but you had to seek it out. In my private practice, the real nexus is when there's fillings. I kind of had an idea, of when to do a filling And then when cusps fractured, I kind of had an idea to do crowns. But there was that time in between when it's too big for a filling and too small for a crown. And traditionally, inlays and onlays were that type of restoration. And I was kind of seeking guidance in those areas. And the guidance that I got from Ray Bertolotti is that the adhesive approach was going to allow these inlays and on layers to be done either directly or indirectly. And so I started to accumulate articles that had to do with adhesive dentistry so that seeking out of articles led me to go to some libraries. The first library I went to was University of Utah Medical School. They had a a library that had dental articles because there were pre dental or actually dental students that did their first two years, the University of Utah. And so I was able to get access to Operative Dentistry and Journal of Prosthetic Dentistry. Those are two of the top ten journals that give us information about conservative operative procedure and more extensive prosthodontic procedures. And the adhesive dentistry articles were coming mostly from Japan. And the Japanese researchers had new products. Ray Bertolotti He had introduced me to a system called Clearfil, and the Clearfil system that I was introduced to came out of what was called liner bond or liner bond one, where all the liner bond one system was actually the fourth generation or the fourth the evolution of the bonding system from Japan. There was a clearfil F one, a clearfill F two and a clearfil F three before liner bond one came on the market and the introduction that I had to an adhesive, an actual dental bonding system was the adhesive from this liner bond. One system. Unfortunately, Ray Bertolotti had simplified this system and taken a bonding system out of it without using other aspects of that system, which were the conditioning step and then the priming step and then the microfilled flowable resin coating step his deductions or his approach to simplification and was actually a dilution of the science that was in these early attempts to create strong dentinal bonding systems. The F one system was a total chemical cure with the monomer which was called phenyl P. Now when we talk about monomers, and these monomers have to have the ability to polymerize. In other words, they need to be able to have a connection that gets larger. And that polymer, that's the foundation of all plastics. All parties have polymerization reactions in those polymerization reactions are initiated with an initiator and these early F, one, F, two and three systems. The initiation was always chemical cure. There was no light aspect for initiating in the liner bond system. This is that fourth generation photo bond that you might guess at a photo activation. And so the photo bond was activated with the initiator that is called camphor quinone. Unlike the initiators of the first three systems, which were a peroxide and the peroxide would interact with the quaternary or a tertiary amine and the amine and the peroxide would start to initiate free radicals, which would start the polymerization reaction of the monomers. Well, the two monomers that were in these systems, first phenyl, P in the F one, and then in F two, the monomer changed from the phenyl P, which is a rather short molecule, but it did have two ends of hydrophilic end and a hydrophobic end. Again, the switch was to ten MDP. This molecule was quite a bit longer and skinnier and so on. Organic chemistry, you talk about stochio chemistry and the stock yield chemistry means how does that molecule fit in with the other molecules, or in this case, the other molecule is of an actual tooth and how the size limits or encourages positioning of these monomers in the in the dentin. Now, again, whoever's listening to this, this may be too much chemistry and you may not be interested, but that's the good thing about our podcast is you don't have to listen to it. But believe me, this chemistry makes a difference. There have been over a hundred synthesis of monomers of different companies trying to make a bonding system that is better than the competition, and they pay chemists to do this. But once a molecule becomes successful, the company that makes it patents the molecule. Now, the patent process is expensive. Company has to pay hundreds, thousands dollars to go through all the lawyers to make sure that the molecule hasn't been patented before and has to explain how it's made. But in a patent, you do have a limit in a kind of proprietary nondisclosure of how you actually make the molecule. You have to disclose what the molecule is. You have to give the structure. Everybody who understands organic chemistry, can look at the patent and say, Oh, this is the molecule. But the company has proprietary ways of making the molecule. But in the long term, these patents are important because one of the gold standard bonding system in the world and there's only three or four gold standards that have been proven to be head and shoulders above the rest. One of these molecules in this system was taken off a patent that was filed in 1951, and in 1992, the Kerr Company hired a friend of mine, Al Kobashigawa who had a masters degree in chemistry from Cal State, Los Angeles, a university very close to where I grew up. I used that library when I was in high school, Cal State, L.A. But Al Kabashigawa was given the assignment from Kerr. We need to get a bonding system. Go for it. So what did he do? He did a patent search. Patent search for adhesive molecules came out that in 1951, a company in England had patented a molecule that was similar to the epoxy molecule and the epoxy molecule that was synthesized first by Castan, a Swiss dentist in Switzerland. But working for this English company created a molecule called GPDM and GPDM polymerized really well, and this original company claimed that this GPDM molecule bonded to dentin, and it was sold in 1951 as the bonding system called Sevreton It's not sevretron, but Sevreton material and dentists bought it in 1951 and they put it in the tooth and it polymerized. But the polymerization of the bond to the tooth was overcome by the polymerization of the restorative material, which was poly methyl methacrylate, which had a shrinkage of about 7 to 8%. Okay, this is history. But like I said, I was a historian when I quit dentistry, so I know the history does matter because when Al Kobashigawa found this GPDM molecule and that it did polymerize well, he also found out that other companies in Japan had tried to synthesize this molecule. And when those chemists synthesized the GPDM molecule, sure enough it did polymerize well, but the molecules did not bond to dentin. And so was the claim followed through? Was the experimentation fault? Well, the ultimate answer. It came out that the synthesis of the molecule that did bond to flat dentin surfaces 1951 it was contaminated during the synthesis process and the contamination was nitric acid. But when the Japanese company sent the size that their synthesis precluded or eliminated this contamination of nitric acid, and so the molecule did polymerize, but it didn't bond to dentin the contamination of the early product that allowed it to bond. What that meant there was a self etching system. They didn't know this. It was an unintended consequence. But the self etching from the nitric acid contamination allowed this infiltration of the monomer and the polymerization, and on a flat surface they got a bond and then they decided to make it into a restorative material that had polymer film effect relate with the eye shrinking polymer and when it was used on a tooth. The c-factor stresses that of course in 1951 nobody knew what C-factor stresses were because they didn't get investigated till 1984. So 33 years later they would have a science that could interpret this early success. But that being said, by the time Al Kobashigawa was working on this, the idea of a hybrid layer in 1982, from the research from Michael Buonocore and then later from Nobu Nakabayashi, gave the idea to Al Kobashigawa that this molecule could be used. Now that we understood how total etch technique that Fusayama pioneered and 1980 could relate to this molecule being effective, and they developed the bonding system that is known as Optibond FL. Well, that's easy because the patent had run out from 1951, and so Kerr could patent again GPDM with the bonding system, Optibond FL and so from 1992 93 until 17 years later, which would be 2000, GPDM was the exclusive to the Opitbond FL system. But as soon as that patent ran out, other companies such as Danville made bonding systems with the FPDM molecule in them, and then their bonding systems kind of piggybacked off the success of Optibond FL. But again, everybody's system has many components, many variables, and the bonding systems that came out of Japan that did not used GPDM because of this early synthesis success that they had eliminated the contamination they still had to deal with how do we conform or how do we develop a hybrid layer? And Fusayama's answer was etching with phosphoric acid. But as they had the first systems, the first two systems with actual phosphoric acid and using phenyl P, then they developed another molecule and this molecule, the longer molecule 10-MDP was very successful in polymerization with total etch. It worked really well, but then they had an unintended consequence, and this is in 1993, they found out that without total edge, this molecule ten MDP bonded to dentin. They tried it with acid etch. It worked. They tried without acid etch, it bonded. Wow. What going on? Well, again, the original unintended consequence of the GPDM molecule in Sevreton that bonded to a flat surface. Again, this happened with the ten MDP and upon further investigation, then they were able to understand that this molecule ten MDP, the P stands for phosphoric acid on the end of the molecule, and this phosphoric acid group made it very hydrophilic because it had three hydrogen ions that was very mixable with water and with pulpal fluid. And so this end of the molecule that was very much great for integrating in a moist dentinal field also had the unintended consequence of removing some calcium ions from the dentin, and then it would make an ionic bond with the phosphate groups in that mean what I just told you, if anybody is still listening to this is very sophisticated chemistry, is inorganic chemistry because we got carbon obviously, or the large molecules that are hydrophobic. But then we have this and that is inorganic chemistry. We got this phosphate in that's interacting in an acid base solution situation. But then making ionic bonds to the actual dentin. And so the first system that totally eliminated the idea of total etch because they did not have to demineralized the surface to create a priming mechanism that the early systems had that came out in 1997 and that 1997 product was called liner Bond two the liner Bond one did have the MDP molecule, but it was in this photo bond adhesive mixture of primer and adhesive. So the photo bond mixed the priming elements and the adhesive elements, and it was used with an etching conditioning step. But the liner Bond two eliminated the conditioning step because the smear layer was able to be integrated in this acid base interaction. And then the polymerization with this ten MDP molecule. And when this happened, it was introduced in 1997, very shortly after that, an improved version of liner Bond two came out. First, there was one called Liner Bond two V, which included photo activation and chemical activation. But finally the photo activation swept the adhesive industry and everything was light cure. Everything was like here. So they eliminated the dual cure aspect of this final breakthrough. They created the gold standard, which is called SE Bond, and SE Bond had the patent of the ten MDP molecule and they had a period of about 15 years where nobody could use that. But again, in 2015, as soon as the ten MDP molecules patent was up, then many companies started to use that molecule as their molecule in their dentinal bonding system. And then next time we'll talk about how they used it and how they misused it, and how the universal bonding systems are inferior to the bonding systems as separate the priming step and the adhesive step. So till next time, get bonded. Stay bonded. Always fun talking to you.