Conventional Cements PDF

So several things I'm going to do I'll be sending everybody in. The DMV shall remember this from last year. I'll be sending you an exam preview. So pretty much if you go through that list and you understand everything on that list, you'll probably do very well in the exam. And I'll send that out. I'...

So several things I'm going to do I'll be sending everybody in. The DMV shall remember this from last year. I'll be sending you an exam preview. So pretty much if you go through that list and you understand everything on that list, you'll probably do very well in the exam. And I'll send that out. I'm putting the finishing touches not quite finished on the exam, so probably early tomorrow morning I'll get that sent out to everybody and read that over and pretty much guarantee that if it's not on that exam preview, it's probably not going to be in the exam. All right. So pretty straightforward. So we were talking about hopefully the last appointment when you're doing an indirect restoration you're hoping that everything's going to fit well. You're hoping everything doesn't nothing has to be redone. So we're at that last last appointment. So remember I talked about fit checker and how valuable that is, especially with with metal restorations. I think it works really well. I found that it's almost a waste of time with the milled restorations because milling actually is much more successful. But the purpose of FID checker is to one verify seating. So even if I think it seats perfectly, I typically will use fit checker just to make absolutely certain because you can see things by interpreting the fit checker. Remember the thinner the better. With fit checker you can see things by by interpreting the fit checker that you can't really see tactically or visually or on radiograph, etcetera. Okay, another reason why you might want to use fit checker is to identify the reason why it doesn't seat. So if you see a show through, or if you see on one side of the crown, it's the protector is very thin and the other side it's very thick. You can pretty much hopefully, although in school here, always get the advice of an instructor because you don't want to start reaming things out unnecessarily. So hopefully you can identify the reason for it's not seating and it could be a bleb. I talked about that last week. It could be a dye defect, and I didn't talk about this last week because that was the last slide. All right. And again, hopefully you'll be able to fix it. But what I don't want you to do. And every so often I hear that this happens in the clinic floor is that people say, well it doesn't fit. So I'll just take a diamond and start reaming out the inside and you're just making it worse. It's you're making the seating even worse. So you can't do that. But you can. If you can identify a little bleb, you can remove it if you identify a small dye defect. And I'll describe what that is in just a second. You might be able to fix it, but always do it with the advice in the supervision of a faculty member. So that's the bleb I was talking about last week. And you can see how it's not seeding. Well, right there it is seeding well over here. And if I took a burr on the intaglio, the inside of that crown and just remove that little bleb and then checked it again with fit checker, I would get a much smaller gap on this side. So I've eliminated the reason. So this is a last slide from last week. And let's pretend that we're doing a restoration either a gold crown or a portion of fuzed metal crown. The old fashioned way, the analog way with with stone dyes and stone models, etcetera. It's not unheard of for a lab technician to drop the dye on the floor and a little chip breaks off. Okay. Remember, if a little chip breaks off the die, what's going to happen? Your restoration is not going to fit. It's not going to fit at all. But it is possible that you can fix it. So if a little chip, let's say that's what it should be. That's what it looks like after it's been chipped. You can actually grind away a little bit of the tooth. Not the die, not the model, not the inside of the restoration. A little bit of the tooth. If it's a very small defect, but do not do this all by yourself. Make certain that that you get a faculty member to to see whether or not that's the prudent, the right thing to do. And if so, watch the faculty member and ask a lot of questions so he or she can explain exactly what they're doing. So the interesting thing is there are limited times where you can actually if it doesn't fit well in your in, you're pretty sure it's because of a chip dye. You can in fact remove a little bit of the tooth. But again don't do that on your own. All right. So bottom line is after you use fit checker, if it seats well and you're happy with it, you just proceed to the next step. If it doesn't seat well try to determine why it doesn't seat well and then fix it if you can. But as I've said already five times this morning, make sure that you ask for the supervising faculty members help in doing that. All right. Once I'm happy that it seats well. Depending upon the type of restoration. And right now we're talking about conventional cementation. At the end of today's lecture, I'll start talking about ceramic cementation or actually ceramic bonding. But once I'm happy that it sits well because the proximal contacts have been adjusted, the internal bleb has been removed. You're really happy because the fit checker is very thin. What I'll typically do then, whether it's zirconia, whether it's used to metal or whether it's gold, I will then lightly sandblast the internal surface and lightly sandblasting the internal surface does many things. One, it removes any junk that might be there, especially fit checker because fit checker is silicone and it can leave some residual silicone on the inside of your restoration, so you want to lightly sandblast it. Sandblasting also creates these little micro irregularities, which increases retention, but more importantly, a slightly rough surface on the internal intaglio of your restoration increases the ability of the wet ability of the cement. And what you want when you cement it is you want that cement to flow nicely without any air bubbles or any air gaps. You really want the cement to flow nicely and then be allowed to set. All right. Whoops. Wrong button again. All right. And again sandblasting can be done either chair side with using something like this. And in your practice when you get out and you can decide what you want to buy, what you don't want to buy, it's always good to have a chair side sand blaster, although you have to be careful of that because you don't want the dust all over the place. It's much, actually much better to use a laboratory sand blaster because it's in a hood and the dust collector is right there, and you're not right there in the patient inhaling all that stuff. So either a lab sand blaster or this. And remember, sandblasting has to be done with the right grit. It's aluminum oxide grit. I'm usually 50 microns and don't get carried away with this okay. And again. Don't do this on lithium silicate like iMacs. Don't do this on on some of the bond ceramic restorations. This is only sandblasting should only be done on zirconia or metal, whether it's gold medal or porcelain fuzed to metal. All right. So lightly sandblasted. Now another option for sandblasting is you can use a solvent like this. This is actually methyl ethyl ketone. But it's a solvent. And this solvent it's really stinks too. So warn the patient when you open up the jar. Don't use this internally. Definitely don't do use this too early. Or if you want to try it, just put a little bit on your tongue and see why you shouldn't use it. Obviously I'm only kidding. All right, so once it's been sandblasted and another option would be to apply a solvent to remove any residual silicone, remove any, any junk that might be there. But sandblasting is actually a little bit better okay. And when it's done is properly sandblasted. Obviously this is a gold crown. The surface will look like this. You can see that the external surface of the outer surface is nicely polished. But although I haven't talked about polishing it, but the internal surface should look nice and frosty or shiny or what's a good word for shiny? Dull. Yeah. Dull. So the internal surface should look a little frosty, a little dull, not shiny. All right, so when you're sure that it seats and the internal surface is properly sandblasted, then you're ready to check the occlusion point that I want to stress is that don't even look at the occlusion unless you've confirmed that it seats properly. Think about this for a second. Let's say you adjust the occlusion first and then you adjust the seating. It's not going to work okay, because now you're in a gross hypo occlusion. All right. So you want to make certain the occlusion. And in some cases finishing the margin should be done after you confirm confirm seating. Because goal number one is to make certain that it seats well. And, you know, use the techniques that have already discussed to to make certain the seats and get the confirmation from your faculty member that he or she is also happy that it seats. Well, all right, now finishing the margin is something that can be done with metal, but it can't be done with porcelain. Used in metal can't be done with ceramic. So if you have a gold crown, you can actually finish the margin. Now finishing the margin means two things one, if the if the restoration is slightly bulky at the margin. With an instrument like a rubber wheel. You can in fact remove just a little bit. But you have to be careful because you want to remove too much. Then you have a it's not sealing well, so the margin isn't really sealing well. So you simply want to make certain that the the contour of your restoration is nice and confluent. And if you have a good lab technician and you've given a lab technician a good impression, you usually don't have to do this, but always check it on the dye. If you have a dye to make certain that it's nice and confluent. If it's over contoured, make certain that you remove just a little bit. With a rubber instrument. Don't use an instrument like a diamond that's going to create scratches, because then you're going to have to remove the scratches and you'll probably remove too much, okay? So be really, really careful with this. All right. Now a week or two ago, I talked about the fact that cast gold restorations, even though we don't do as many cast gold restorations as we did in the good old days, a beauty of a really strong positive of using cast gold for inlays and inlays is you can actually burnish the margins. And I sort of alluded to this, but I'm going to go through the technique if in fact this is your tooth and this is like maybe a 30 degree bevel. All right. So this is the finish. That's the finish line of your tooth. This is the cast gold. Let's say it's type two or type three. Usually type three cast gold. Right. And it's on the occlusal of your inlay. So you have an inlay that when you take the sharp the tip of a sharp explorer and you run it, you can actually feel a little ping. Okay. So one way to improve that, that confluence, a one way to improve or get rid of that ping, is to simply take an instrument and push on this gold this way. And again I'll describe two ways of doing it. And remember burnishing means push. All right. So the reason why you can do it with gold is is gold hard or soft. It's relatively soft. Obviously it's not soft as jello, but it is relatively soft. It's also malleable, which means it can bend a little bit and it can be extended. So if you put enough force on a thin margin of gold, you can actually get it to do this, okay. Because you can bend and elongate that thin margin of gold so that it seals much better. And obviously this margin is going to be better than this margin, right? So that's an advantage of doing an inlay or an only using cast gold. And again, I keep saying this, but it's a shame that you guys aren't going to be doing a lot of cast gold. Now, how do you bend it? And the answer is, well, you could theoretically use a hand instrument like a ball burner. Sure. Or beavertail burner, sure. Or the whole number of different types of burners that you could do, but that's a little unrealistic. It's actually much easier to use a rotary instrument. So in your slow speed handpiece, moving relatively slow, you know, maybe 5000 RPMs on an electric handpiece, you can put a white poly stone, which is a white little white stone, a mounted stone, and lubricate it with Vaseline, okay. And then rotate it slowly this way. Don't go this way. But it makes it. The white stone lubricated with Vaseline is going this way. And that will, in fact take a margin like this and turn it into a margin like that. And it's unbelievable how well this works. All right. So again, before you do it, it pinged. After you do it, you can't feel any margin at all. So it's a real great way. Now can you do this. On the gingival margin. In the mouth. No, unless there's no tooth next to it. So theoretically, maybe you could if there's no tooth next to it. But the, the the value of, of burnishing a gold margin is that you're doing it on the. I'm sorry. The buckle, the lingual, the occlusal of your inlay or on light, but you can't really do it on the, on the gingival margin. But that's okay. All right. So a white poly stone lubricated with Vaseline slow speed heavy pressure and make certain that it's rotating in the right direction. Remember there is a little control button on the delivery system in both in the SSC and the clinic that will reverse a slow speed handpiece. I don't even know whether you're aware of that, because obviously for excavating, we always have it going in the forward direction because of the the orientation of the blades. But if you if it goes in the opposite direction, you can actually use it to push. But don't use a anything other for burnishing anyways. Don't use anything other than a white stone. All right. And again, when you're all done, you go this way and that way. You just simply can't feel anything. And it's probably the best seal that you're going to get. All right. Now. This is done in the mouth. Okay. But then you remove it because there's one final step and that's finishing and polishing. Right now let's talk about two different things. If it's gold, there's a finishing polishing system that can be used. If it's ceramic, there's a finishing and polishing system that you can use. But ceramic is probably already pretty, pretty well glazed or pretty well polished, so you don't have to worry too much about that. All right. So let me talk about how to get an unbelievably good shine with cast gold. Okay. And it's dirty. Okay. Sort of like I briefly told you about polishing amalgam. Remember that. Actually, you should remember that for the exam because there are a few questions about finishing and polishing amalgam. All right, so for cast gold. Step number one is to eliminate any gross scratches and make certain that the contour is right. So I will typically use a rubber wheel to do that on a slow speed handpiece. Once I'm happy with all of the contours and all of the margins and eliminate elimination of any obvious scratches, I'm going to use a compound a polishing compound called Tripoli. Put your hand up. If you've ever heard of Tripoli as a polishing system, it's actually interesting. Looks like a brown bar of soap. Or sometimes it's a cylinder. Sometimes it's like a little bar. Okay? And you take an instrument like a soft bristled brush on you slow speed, straight handpiece. Okay. And you kind of run this on this bar looks like a bar of soap, but run it on the Tripoli and then go to the, to the restoration and go over the entire external surface of your restoration. This is a little tricky with a little mo inlay. Really tricky. Right? So you've got to have good hands and make certain that if it if it flies across the room, you and your dental assistant are able to watch where it flies to. All right. So I'm going to work over the surface with Tripoli first. Okay. And then I'm going to switch to a second polishing compound called rouge. Rouge means what? Right. So it's red. Okay. Sort of red. But you don't want to use a brush. The best instrument to use is a very soft wheel. And you have two choices. A felt wheel or a shammy wheel. Looks like chamois, but it's a shammy. And what is shammy? And the answer is. It's an ultra soft leather which frequently can be used well, not the same wheel, but you can use shammy to wash and wax your car well, don't wash it. But putting the final luster on your car, I don't know, not this time of year. Don't do it this time of year. But this is a shammy wheel simply rotating and taking that good luster that you got from the Tripoli and making it even better. Luster. And it's incredible. You get it literally. You can see your reflection, like looking at your reflection in the mirror after you've done this. So a rubber wheel removes any scratches and gets any contour or anything. It's hyper contoured, eliminated. Then you're going to use a bristle brush with Tripoli and either a felt wheel or shamooael. With rouge, it makes certain that you follow that sequence. Don't use the rouge first and then the Tripoli. Okay? And of course, a much easier way to do it is to I'm sorry, much cleaner way to do this is to buy a gold polishing kit from a company like Shofu, which is probably the number one vendor for making polishing stuff, polishing instruments. But they also very similar to what I talked about. With amalgam, you follow the same sequence of using brownies than greenies, and then if you really want to impress an instructor, use a super greenie, okay? Because again, that's an incredibly high luster. Many people feel that this isn't necessary, that what you can get with the Greenie is superb now. If it's a ceramic restoration, obviously you want to finish it, not with with metal polishing kits, but with things that are designed for the specific type of ceramic that you're using. So, for example, if the ceramic that you're using is lithium bi silicate, you want to use rubber wheels or rubber instruments that are designed for polishing lithium silicate. If it's zirconia or if it's seltzer duo, you want to make certain that you're using the appropriate rubber wheels, and you can get a really high polish on that, too. Now, don't forget to do this once you've polished, especially the dirty way with Tripoli and Rouge, you're probably going to get junk in the inside here, so you're going to have to clean that out again. Okay? It doesn't make any sense to if sandblasted again, because then you're probably going to sandblast out here okay. So use a solvent like carve a dry. There's another brand called Cadillac's LA Cadillacs or Caviar Dry. And it's simply a solvent that nicely removes the junk that that may, may be inside here. And you can see little pieces of junk inside there. This is probably a little remnants of Fit checker. And you simply put a little bit of this inside that, scrub it and wash it dry. Okay. Now the inner surface just before you're ready to cement it. Remember all of the adjustment has now been done. Okay. You've adjusted the contacts that's necessary. You've adjusted the occlusion, you've verified seating, you've gone over the margins. You've got margins that are beautifully confluent. The external surface has been polished to a high luster, if that's appropriate. Now, what I now want to do is make certain the inside is clean and dry. That's the purpose of using the Cavalier or Caviar dry. It's already been lightly sandblasted, so there's usually no reason for sand brass re sandblasting, if that's such a word. So you have an internal surface that's very slightly not very rough. There's slightly rough and has high surface energy to maximize wearability or maximize the wedding of the cement, because that's really what you want to do. Remember, you don't want to you want to seat this when you're ready to cement it with very firm pressure, okay. And make certain that the cement flows very nicely beyond the margin. Okay, so just as a review of the try and before we get to the actual segmentation, make certain that you have assessed the proximal contact. It's either one of three things. It's either going to be perfect too much or too little. The proximal contacts. And again you don't have to fix it if it's just right. But the other two are usually fixable. Okay. And then you want to make absolutely certain that you assess whether it's seating properly. And. Try as hard as you can to maximize seating. You want to make certain that the occlusion is the same occlusion I talked about with composites. The same occlusion I talked about with amalgams with amalgam. Remember, the only time you want to change the occlusion is if you're an orthodontist, you want to change the occlusion. If you're doing a full mouth reconstruction, you want to change the occlusion. If you're making a complete denture because the patient doesn't have an occlusion in that case. All right. So so with single tooth restorations, crowns or even fixed bridges, you don't want or even implant supported restorations. You don't want to change the patient's occlusion okay. And again if appropriate finish the margin. So they're perfect. Put a final finish and polished okay. And then make the inner surfaces nice and clean. And then with that beautiful restoration attach it to a pick and stick. Remember what I when I talked about the temporaries last week or the week before, whatever it was, who knows? A little object holder like a pick and stick is invaluable, especially for tiny little inlays. Okay. All right. Now one more decision has to be made. And that's what cement you're going to use okay. So what are the choices today in 2023 almost 2024. What are your choices of cement. Don't say anything. I just want you to think. Can you make a list of several options? Okay, so let's look at them if I had to. Well, let's pretend that we're working for a company that makes dental materials. And the boss came to us and said, okay, here's your job. I want you to come up with the perfect cement. For cementing indirect restorations. The perfect cement. What would it be? And the answer is it would have to have these and actually a few more. Okay. So the cement has to be hard and the cement has to be strong, right? And the answer is sort of. But it's so thin. Strength and hardness isn't the most important thing, even though you might think that it's the most important thing. Of course it has to be. It might be the most important thing if your restoration doesn't fit well. Right? But again, if it does fit well, does sleep really well, the amount of cement is going to be so minimal to strengthen. The hardness isn't just as important as you might think. Now what about solubility? Do you want to cement? It's soluble in oral fluids. Most historically, most cements are soluble in oral fluids. Okay, which doesn't make any sense. Advanced students. Have you ever seen an old crown with cement wash out? Have you ever removed an old crown? And you look at the inside. Okay, now you probably cut it in pieces. And you look at the inside. And there's all kinds of schmutz on the inside. There's not clean cement anymore. And that means it's been dissolved away because it's soluble in oral fluids, especially something like zinc phosphate cement. Okay. I would love a cement that was adhesive. To what? Well, it's right there to everything, right? True. Adhesive dentistry for cement literally means it's adhesive to the prep, which implies enamel, dentin, core material, any old remnants of filling material, any base or liner that you may, may have placed. So I wanted 100% adhesive. Remember, adhesive means short term and long term. I want to make certain that it sticks. Now, today, I want to make certain that it's maintains that adhesion over long periods of time. So durability of the bond is important. But to be perfect a perfect adhesive cement would also be very adhesive short term and long term to the inside of the restorative. So if it's a crown, the inside of the crown, if it's only the inside of the online. All right. So if in fact it's perfectly adhesive to both sides and it's insoluble in oral fluids, it's a pretty good cement right now. Biocompatible okay. The reality is is almost all cements are biocompatible. But obviously biocompatibility is something you want. Biocompatibility in relation to two things the lining of the sulcus. Because again, if you've placed a, your preparation is slightly sub gingival, even if it's in a perfectly normal sulcus. You don't want to cement that tiny little layer of cement that's right at the margin. You don't want that irritating the lining of the sulcus, but you also don't be irritating the pulp. And I can tell you a cement like zinc phosphate cement was very irritating to the pulp. Okay, so again, things have changed. Now what do I mean by low film thickness? And the answer is I want to cement that flows so well that when you're seeding it to place for the final time, remember you're not trying it anymore. You're putting it in permanently that the cement flows so easily that it goes down to maximum thinness or minimum thickness. Same thing. Right. All right. So you want it nice and thin, but you also want to maintain its properties in a thin layer okay. So it's important that you have good film thickness. And again darn some of the. Some of the cements don't have great film thickness. Poly carboxylate cement, like Dalton, is notorious for having a thicker than normal film thickness, and you have to really push it to place when you seat it. Okay, now if you are really in charge of coming up the perfect cement, it would have to be cheap because dentists don't buy expensive things because we're cheap. You know. Most of us anyways. I'd also like a memento is technique insensitive. Which means what? That if you're a little bit sloppy, it'll still work. Remember, that's what technique sensitivity is. Something is very technique sensitive. If you don't mix it properly, if you don't proportionate properly, if you don't seat it properly, it's not going to work okay. But it's insensitive. Simply means if you can mix, you can eyeball the mixing. You can. It's not that important. But I'd like one that was technique insensitive. All right. Now what do I mean by therapeutic Nazis? I'd like to use a cement that that isn't just inert. It does something positive for the tooth. Maybe it has fluoride in it like a, like glass. Cements have fluoride. That creates a somewhat of a zone of caries inhibition beyond, you know, around the cement, good old fashioned zinc oxide huge and all was therapeutic because that's huge and all in it. And huge knowledge is classic for for sedating a pulp or decreasing the possibility of postoperative sensitivity after a crown is cemented. Right. So again, therapeutic is nice. And there are some bioactive materials right now that are saying that they promote hydroxyapatite formation. Okay. So again, maybe that's the future a lot of people think that it is. Is that in the future, back when you're well established in your very successful practices, you might be using a cement that makes it almost impossible to have carries around it because it's so, so full of fluoride making hydroxyapatite. ET cetera. All right. Now, why do I need esthetics? Because especially for certain types of restorations, I want to cement. That gives me the ability to either lighten or darken a tooth a little bit. So, for example, a lithium d silica crown on tooth number eight, you might actually be able to not not to a great extent, but you might actually be able to make a minor change if you're cementing veneers. I might want several different shades of cement for cementing veneers, because I can actually change the appearance of the veneer by using a slightly higher value or a lower value cement. So again, this may or may not be necessary obviously for inlays and it's not necessary most of the time. Now I'd also like a cement. And this is where we come into into a problem or dilemma. I'd like a cement that is easy to clean up after it's been seated because again, removing we've actually created a monster because when we used to use a lot of zinc phosphate cement, it was easy to remove excess cement because it wasn't all it wasn't adhesive, it wasn't all that strong. And it was soluble in anyway, so it was probably going to dissolve away even if we left a little bit. But nowadays we're using adhesive adhesive resin cements for a lot of restorations. And if you leave a big wad of excess cement into approximately between two number two and two number three, you'll probably never be able to remove it. And it's not going to dissolve away. All right. So on the one hand I want a super cement. On the other hand I don't want it to be too super okay. And this is also true. I also don't want to cement it so good that it's going to take two hours just to remove the crown 30 years later, when it has to be when it's chipped or anesthetic and it has to be replaced. All right. So again these two things go counter to some of the other properties I'd like to have. And of course, as with any new cement or any new dental material, I'd like one that is time tested so that we know it's durability. Remember, if something is brand new, do we know how long it's going to work? No, of course not. All right, so here are our choices. Good old fashioned zinc phosphate cement. I have no reason to to ever use this. But it's it was fun mixing it and it was fun. I'll show you the technique of mixing it. But for many, many decades, zinc phosphate cement or zinc oxide phosphate cement was the norm. It's what most of us cemented our gold crowns with up through the 1980s. So zinc phosphate has been around for a while. Poly carboxylate, the most common brand name is Dalton, but there are other other polycarbonate cements. And this is actually the first somewhat adhesive cement because it bonded to to dentin and enamel. Not well, but it bonded. There was some adhesion to enamel and it also bonded to stainless steel I don't know. So pediatric dentists might use stainless steel to cement stainless steel crowns with Dalton. But it's not a great cement. But it was really the for a short period of time. It was the only legitimate alternative to zinc phosphate cement. So in my career, I started off using a lot of zinc phosphate cement, and I tried poly carboxylate with with some good experience, some not so good experience. And then we started using glass items but not resin modified glass or as conventional glass monomers and then resin modified glass cinema. Okay. So these four are considered conventional cements or looting agents. Remember what the word looting means? Looting means it's just a space filler. It's not really adhesive, even though poly carboxylate and glass is a somewhat adhesive to tooth to, not adhesive to restore the materials. Okay, other than stainless steel crowns and stainless steel power posts, for example. Right. So the others and these are sort of related are like your resin auto cure resin and dual cure resin. And these are essentially composites with either no or very few filler particles in it. Okay. But it's either best GMA urethane dimethyl acrylate or the conventional resin component. And you can buy like cure. Now why would you use like your only. Where would you use like your only. And yes, there's veneers because it's a little bit more color stable. It's much easier to use. Okay. And because veneers are so thin, the blue light is going to go right through the veneer and make certain that you get good depth of cure. So like your resin cement is really only indicated for veneers okay. Auto cure resin. It's used very infrequently today because this is a resin that will only set when two things are mixed together. It's not like curable at all. Okay. But for example, there was the earliest panacea. Have you ever heard of panacea? So the earliest panacea was actually a I'm sorry, 2120 first century. Get it? But Navi 21 was actually a self cure only it had no light curing capabilities at all. And most of the good resin cements today, especially for inlays and inlays and ceramic crowns, are dual cure, which means that it's going to cure chemically because you have to. You're going to mix two things together to initiate the chemical reaction, but you can also cure it when you want. If you want to cure it a little bit faster, you can take your light and cure it. And again. The beauty of that is that the chemical reaction will make sure that the deepest, darkest areas of the cement will set. Okay. And the like here means the more peripheral part of the the cement will set, allowing you to go on to the next step and allowing you you can check the occlusion. It's okay to let the patient get it wet. Once it's it's attained it's dual cure set. So let's talk about. Very briefly, because I don't want to spend a lot of time talking about archaic materials, but zinc phosphate cement. And I say zinc phosphate paradox. Now. Why? What do I mean by a paradox? It means it doesn't make any sense. Ever hear of the French paradox? No. Okay, well, French paradox is a classic paradox, saying in general, people from France eat stuff they shouldn't eat. I drank way too much wine. They drink way too much fatty food, all that. But they're always skinny. All right, so it's a paradox. It doesn't make any sense. All right, so the issue with zinc phosphate is that is it a good cement. And the answer is no. Did it work well? The answer is yes. Didn't make any sense. Right? So why is it that zinc phosphate cement. In spite of it having bad properties was a successful cement. And the answer is now I'm going to go back to when I was in dental school. We were told over and over and over again that the cement was unimportant. And what's more important is that the preparation is retentive and the restoration fits well. And if you have a highly retentive preparation and a restoration that fits well, and this is literally what I was told by my chronic bridge instructor when I was in school, is that jello will work. Okay as a as a cement. And I can remember the very first I hated this very first bridge I did was a three abutment, four unit bridge. And I was convinced that the taper should be like 1% okay, because retention is more important than breathing. You know, it had to be highly retentive. So I was told by my instructor to cement this bridge with temporary cement so we can check the occlusion and we can bring the patient back next week to make certain everything's comfortable. And I never got the bridge off, even though I cement it with temporary cement, because my three preps were, like, extremely retentive. And this is a type three gold bridge, so no porcelain fuzed to metal. It was all gold and fit extremely well. So the reason why this is an important statement, the reason why zinc phosphate was so successful is that we were told it was a bad cement. So our prep had to be perfect and our fit of the restoration had to be perfect. And we concentrated so much on that that the type of cement was actually not important. All right. So zinc phosphate is an inexpensive and familiar looting agent with over 100 years of success, even though it's not a great cement. All right. So why did zinc phosphate work so well? All of these guys. This is my class. No. All of all of these guys concentrated on making certain that their restoration fit well and was highly retentive. So. So it is still true, even though some of today's cements are much better than the old cements. If the if the restoration fits well, if you have a highly retentive and resistant prep and you pay attention to detail to mix the cement properly. Peanut butter would work. Jello will work. You know, those kinds of things. Okay. And the choice of cement is actually not as important. So that's what we were taught okay. And I think it's true. And here's the the proof. Now I don't do a lot of custom abutments for implants anymore. But when I used to do a lot of custom abutments, the abutment would actually be made by the lab. So if it's a regular crown, I do the prep, okay. But if it's a custom abutment on an implant, the prep is actually made by the lab and it has to be perfect. They actually do it on a milling machine, right. So they have six degrees of convergence. They have perfect retention. They have perfect occlusal reduction. Perfect axial reduction. Because the lab technician who's going to be making the crown is actually making the abutment. Okay. And when you have perfect preps like this okay. Especially in the early days of implants where we wanted when screw loosening. Screw loosening was a common problem. We wanted to be able to remove the crown if necessary. Okay, because we weren't doing much of any screw retained crowns, right? So a lot of these, even if you cemented it with with temporary cement, you would have a hard time getting it off. And remember that story I told you about my first four unit bridge? What really ticked me off about that for a year in a bridge, as we couldn't get credit for it until it was finally cemented. So I didn't get credit for four units of Crown of Bridge that I never mind. All right, so zinc phosphate cement has been around well before GV black. Well actually GV black was born after this, but so it has an extremely long track record. It wasn't exactly the same formula, but it was almost the same formula. And for for decades and decades, it was considered the standard to which all other cements would be compared. All right. And again, the nice thing about zinc phosphate cement, if you want to mix it to a thicker consistency, you can use it as a base or a liner or a blockout material, because it was easy to vary the consistency. And I'll show you why in just a second. One of the bad news pieces of bad news about zinc phosphate cement is that right after it was mixed, it had a pretty low pH. Okay. And if you didn't anesthetize the patient and you see seated a crown with zinc phosphate cement, they went through something called the zinc phosphate sting because it tastes it felt like it was stinging okay. Now eventually most of the time anyways, it settled down. So we were actually taught and we did use a cavity varnish on our preparation. And I'll explain what cavity varnish is a little bit later. All right. So this is it. I took this slide a long, long time ago. What's interesting is about 5 or 6 years ago, a prosthetic resident came to me because I looked old and he said, have you ever mixed zinc phosphate cement? And I said, sure, of course. Okay. So he said, can you show me how to do it? Because I'm doing this lecture on cements, and I want to take pictures of mixing zinc phosphate cement. So I said, I'll show you exactly, but I need a glass lab and I need the powder and liquid from zinc phosphate cement and a metal spatula. So this is how you mixed it. You took a thick glass slab out of the refrigerator. Why in the refrigerator it says it had to be chilled and it had to be thick. So your dental assistant would run to the refrigerator, take it, bring it back to the operatory, clean off any moisture or condensation on it, okay. And then put several little drops of the liquid on this side, okay. And several little mounds of powder on that side. Okay. And then one scoop at a time, you would spread it out over a large area. Now why the chilled slab? And yet if this slab is not chilled, it will set almost immediately. So it doesn't give you enough working time unless you it's mixed on the chilled glass slab, and it had to be mixed little scoops at a time and spread out over a large area until keep bringing another scoop, another scoop, another scoop until it had this. This is referred to as the looting consistency. Looting consistency means you lift the spatula about an inch off the chill glass slab and it stays like that. Okay, so this is referred to as a looting. I don't know why I'm even talking about this, because this. So I don't know, it's nostalgic. I get so this is referred to as alluding consistency. And this is what you want. If you wanted to use this cement as a blockout material or as a liner or a base, you could actually bring in more scoops of powder and it will start forming almost a putty like consistency. All right. Now, as I quickly alluded to and I mentioned this to the DMD students last year, I'm going to remind the students a little bit later this year is that this is a very popular lining material when you're using amalgams or zinc phosphate cement to help protect the pulp. Put up your hand. If you've ever heard of cavity varnish. Okay, first of all, you shouldn't be using it because it's really, really old fashioned. But cavity varnish is actually copal resin in the solvent of either acetone or ether. It had a very distinct I'm sure you could get high if you kept sniffing it long enough, right? But it was very simple to use. You simply dip the little applicator into this liquid. This is back before infection control was in vogue and you simply painted it on your preparation. The purpose of this was to seal off any cut dental tubules. Okay, that was the reason why you would use it, but you shouldn't use it anymore because it interferes with polymerization of composite. Okay? And you shouldn't use it for anything adhesive because it forms a barrier. So adhesives won't work. All right. So that's why Coppola really has no no indication at all anymore. All right. Now that's zinc phosphate cement. And we were told in order to avoid the zinc phosphate sting, to paint the preparation with coprolite before you submitted the crown. And that was routine. And plus, you always want to anesthetize the patient. So they didn't have that sting. All right. Now poly carboxylate cement was, as I mentioned earlier, was the first real alternative to zinc phosphate cement. And it was very exciting because we were told that this absolutely is somewhat adhesive to to structure. And it's extremely, extremely pulp friendly. Okay. So it's very kind to the pulp. No such thing as a zinc phosphate sting. You don't get a poly carboxylate sting. All right. So this is an interesting cement. It just wasn't very good okay. And it was hard to mix. The consistency was usually two to thick. And unless you really put a lot of pressure on your crown when you're seeding it, you may not get that good film thickness that you want. But. And which is the the brand leader, as I said, is the first real alternative to the zinc phosphate, the first somewhat adhesive. And the reason why I say somewhat adhesive is it didn't stick to the inside of the crown or didn't stick to the inside of the restoration other than stainless steel. All right. Very, very, very kind to pulp. Okay. And again, it was considered the most biocompatible of all of the materials. But the properties were not great, especially solubility. Okay. So it would dissolve in oral fluids. It didn't have very high strength. It didn't have very high hardness. And dental assistants didn't like it because it was too thick. In fact, the liquid wasn't liquid. It was like a almost like a gel. It had almost like a syrupy, like a honey, like consistency, the liquid. So it wasn't all that easy to mix, okay. And it was just disappointing. So. You know, personally, I used it for a year or two and then said, forget about it. I've seen too many crowns fall off. I've seen when when they do fall off. I've seen a lot of solubility in the inside. Ah, so it was just too disappointing. Okay. And then, I mean, the nice thing about dentistry is you wait long enough something new and improve is going to come along. All right. So eventually conventional glass cinemas came around okay. And these are two very common conventional glass cinemas. Ketek Sam was a good one. Fuji one was a good one. These are conventional glass cinemas that were much more popular in Europe and in Japan than they were in the United States for a long, long time. So it took us a while to kind of jump on board. And, you know, obviously Glass Cinema can be formulated by the company to either be a filling material or a cement or a liner or a sealant. Right? So again, that's not up to us. That's up to the manufacturers to come up with different consistencies and different flow abilities. But these are pretty good but also disappointing. So Glass Cinema Cements used first outside this country where powder and liquid the powder was fluoro aluminum silicate glass. The key there is fluoro okay. And the liquid was poly acrylic acid, which was actually the same liquid that was in poly carboxylate cement. And it didn't polymerize. It was an acid base reaction. Of course, when you mix an acid with a base, you get a remember the chemistry class who said salt. Very good. All right. So you get salt okay. So it's not a true polymerization. It's not a polymerization reaction like it would be with composite okay. And you get chemical adhesion to to structure which again was very nice. And as I mentioned earlier there were several different types to face depending upon what you wanted to do. So you could use it as a filling material, you could use a cement, etcetera. All right. Now, in terms of the properties. What's the one word that comes to your mind whenever someone says glass eye on? Yeah. The Fword. Fluoride. All right, so as soon as you mention glass, you should say, oh, yeah, that's the fluoride releasing one. Right? That's true. All right. But it has a has other properties that make it really good. One is it's chemically adhesive to two structure. Now remember there are two ways of adhering something or two structure micro mechanically and chemically. Micro mechanical is good for immediate high bond strength, especially to dentin and enamel. But chemical bonding is actually better for long term durability. The problem is that it takes a while for the chemical bond to to take effect. That's why in the early use of glass animals, we were actually told not to finish and polish it. When you did it. For example, we were doing it as a class five restorative material. We were told to cover it with a cavity varnish, and then wait at least a couple of days until it was fully set and fully bonded, because it took hours and hours and hours for glazing conventional glass to bond to to structure. All right. And fluoride release charismatic. And the only comment I'll make here is that don't think if you use a glass it's impossible to get secondary caries. That's not true. It's just less likely to get secondary caries. Okay, so it's not perfect, but it's good. But it's not perfect. All right. And strength and hardness were good. Biocompatibility was good. Film thickness is very good okay. So lots of good properties. But here's the bad news. When we started using Ketek Sam or Fuji one. Because it sounded so good. We would get one out of five, one out of ten patients who would experience significant post-operative sensitivity. Okay. And at first, nobody could figure out why because a lab test said it was biocompatible. The lab test said it was. The pH was nice and close to seven, so you shouldn't get post-operative sensitivity. But we did. And one out of five is not good because if you have to redo one out of five crowns that you do because of a weird post-operative sensitivity, you'll go broke and you won't. You won't gain a lot of patients confidence. Okay. If one out of five of your crowns has to be redone because of this weird, unexplainable post-operative sensitivity. All right, so here's the issue. Conventional glass cinema was very slow to set. The setting time was like ten minutes. Okay, okay. And it was not easy to maintain moisture control, especially when you're cementing a crown on tooth number two or cementing a crown on tooth number 31. Right. So it was the slow, vulnerable setting time that would allow for the cement even before it's set to to wash out, because the moisture would get up underneath the crown and dissolve away some of that moisture. So very susceptible, sensitive sorry sensitive to both moisture and and dehydration. And it was because of the very slow and very vulnerable setting time. Okay. But we didn't know that at first. All right. And as I said earlier, one out of five, one out of ten is way too many failures especially, you know, is there anything more frustrating than getting a perfectly fitting crown, a beautiful esthetic result, and you cement it and the patient calls back like two days later saying, I can't even look at ice cream because my two, my tooth throbs every time I drink something cold. Make your day right. Okay. All right. So, in fact, this was an interesting article that I took a picture of a long time ago, and I can't even remember this guy's name. But anyways, I have absolutely nothing positive to say about glass or cement. So we're just seeing the tip of the iceberg in terms of post-operative or whatever. So this guy actually stated in this article that it was malpractice to use glass of cements because of the high incidence of unexplainable problems. Okay. And when you remove the crown, this is what you would see. Okay. And this is a crown. I don't remember the exact time, but this was actually relatively soon after. It was cemented like a month later. And you already see washout. But that washout didn't happen over long periods of time. It happened almost immediately while it was going through this slow, vulnerable setting time. Okay. All right. So. Just like poly carboxylate cement sounded great. Pretty disappointing. Conventional glass sounded great. Little disappointing, in fact. Really disappointing. Okay, but then the chemists who make glass and cement figure out a way to make it much better. And the answer is resin modification. So resin modified glass cements are now the number one conventional cement in the universe. Well, at least in Earth. All right. So remember when I say conventional cement I'm not talking about resin cements. Those are adhesive bonding cements. Conventional looting cements are things like zinc phosphate poly carboxylic conventional and resin modified glass cinema. All right. So relics looting which is now relics looting plus Fuji plus these are really good resin modified glass items okay. So resin modified glass animals our true glass monomers, they do release fluoride. They do have chemical bond to to structure. And they're light curable. So the true glass monomers but much better working properties. You don't have to wait as long and you don't have to maintain contamination control as long as you would with conventional glass monomers. Okay. And it actually tolerated a little bit of moisture and tolerated a little bit of dehydration with no post-operative problems. Mechanical properties are better because you add a little bit of resin. You make it harder and stronger. Okay. The adhesion was actually better as well, and it released fluoride. So the question became. If this is much, much better, why would you use conventional glass cinema? And the answer is most of us stopped using conventional glass. Most of us started using resin modified glass armor, which has now been around for over 20 years with a huge amount of success. The numbers of failures I've had, the numbers of post-operative problems with zinc, with resin, modified glass. The armor is very close to zero, so it's a highly successful cement. And finally we have the first real, real, real true alternative to zinc phosphate. Because with a with a polycarbonate and the conventional glass cinemas, we were too disappointed. But we weren't disappointed with resin modified glass cinema. All right. Okay. Now the only argument about resin modified glass is that it does swell a little bit. So it does expand slightly, but in most of our opinions it's not clinically significant at all. In fact, maybe it's better that it's slightly swells. Maybe it fills, it fills in some little gaps. So let me show you. Now let's stop. Let's take a do the QR code and I'll give you a short break. And did you notice a new. What is this, a podium or a lectern? Is this the podium, or is this the lectern? No, this is the podium. Okay, this is a lectern. How often are those two words used improperly? Yeah, all the time. So most people say this is my podium. It's not. All right. I don't know why I'm even talking about stuff like that. Well, who puts this on caps? I don't know how to spell my name. Rob a Cronulla. Now that can't be. Oh, dear. Okay. We're going to start up again at 11:00. So do the sure thing and then go to the restroom if you have to. Troops. Yeah. Okay. How? Oh, that's. So anybody who still needs this? Nope. Okay. 11:00. Now, a couple of weeks ago, I talked about the fact that mixing things is becoming much easier than it used to be. And I was talking specifically about impression materials. We also say the same thing about cement. So I'm going to talk about two different. I'm going to talk about a very significant trend in dental materials or the delivery system for dental materials. Now let's look at one of the earliest resin modified glass. And I think it's the market leader. I think more people use rely excluding cement than almost any other cement. It's a great resin modified glass that originally was in a powder liquid form. So you mix the right amount of powder with the right amount of liquid, and I can quickly show you the technique. One is to take the powder and shake it so you fluff the powder so it doesn't settle to the bottom of the thing. And that wasn't me moving my camera. That was my dental assistant doing this to make certain that the powder was fluffed. Okay. And then three little scoops of powder were put on one side of the paper mixing pad. Then three drops of free flowing liquid was placed over here and then it was mixed. Into a quote unquote looting consistency. It was mixed into a nice fluffy looting consistency. Now the problem with powder liquid, it's notorious for being non standardized. So if you have one dental assistant mixing compared to another dental assistant mixing compared to another dental assistant mixing, they are all different slightly different proportions. It's all like if you were a baker, you know, like on that English baking show. So let's just say you are a baker. If you're a really good baker, you can eyeball stuff. I'll tell you, one person's scoop of flour is different than another person's scoop of flour. One person's cup of of liquid is different than another person's cup of liquid. So the single biggest problem with powder liquid anything is inconsistency of mixing. And it's more time consuming. So frequently you don't have the right proportions of the powdered liquid simply because of this inconsistency. So the trend that I was just talking about is going from powder liquid to paste paste. Okay. Now why is powder liquid? I'm sorry, why is paste paste so much better? And the answer is as long as you use a gun like this properly, okay, it's almost impossible to have unstandardized mixes of the two things that have to be mixed. They're almost always the same. And if you did a study with 100 dental assistants using this, they would all be exactly the same consistency because the proportions were exactly the same. Plus they could mix it much faster, much faster than this. And even now there's little thing you can put on the tip that auto mixes it. This earlier version just put out the right proportions. The newer version not only has the right proportions, but also has that little baffle tip on it that you can inject directly into your crown or directly into your your restoration. But again, this earlier version simply had the right proportions. All right. So clearly the trend and this is going to be important when we talk about other things in dentistry as well. The trend is away from the hard to mix things like chilled glass slab and zinc phosphate cement to just squeezing something or pushing a button for much, much easier dental assistance. Their job is so cushy nowadays. All right. Okay. And then of course, once it's been mixed properly, do you fill up the crown with cement? And the answer is no. You coat the inside of the crown with cement shortly after it's mixed. You coat the inside and then seal it with very firm pressure. Remember, you don't want to screw up now. You don't want to make a big mistake now by not seeding it with firm enough pressure. Because then what are you going to do? Okay, some of the earlier auto curing resin cements were notorious for setting too fast. Think about the problem with something setting too fast. Okay, I have 3 or 4 examples of students who are slow because their students. Okay. And they were taking their time because I want to get the instructions, follow the instructions properly. And by the time they went to seated it was starting to set. So a crown would be like half on. And the cement was getting harder and harder and harder. Okay, now what you should do is take it off as quickly as possible. But a student would probably just keep pushing. Okay, so what do you think would happen? The crown is now half cemented with a cement that's rock hard. Okay. And what do you have to do now? Well, first off, you student, you have to go to an instructor and tell the instructor what you did and be ready for. Oh yeah. So the instructor will then have to come over and help you remove it. And of course, the patient is saying the student doesn't know what the hell he's doing. All right. So. So for a whole number of reasons, you don't want something to set too quickly. All right. So again, coat the internal surface of this and seated as quickly as you can. All right. So this clearly and this is just another brand. This isn't from three MSB. This is from GCC America. The trend in a lot of different materials is going from powder liquid to paste paste. All right. And again this is simply a GC America's dispenser for dispensing the appropriate amounts of the two things that have to be mixed together. All right. So today is a very important statement. Resin modified glass is by far the most popular general purpose looting cement. Most of us restorative dentists, if we're cementing a gold crown, use this. If we're cementing a zirconia crown, we use this. If we're cementing porcelain views to metal, we use this. If we could use this to cement posts. Okay. So there are a whole number of kind of general purpose cements and the only viable alternative today. Is. Resin cements. Okay, so today if you are starting a practice and you wanted to be frugal and you didn't want to buy something you weren't going to use, all you really need is two cements. You need a resin modified glass, either from Fuji, the Fuji products or the the Relix products, or I'm sorry. And you need a good resin cement, probably a dual cure resin cement. So if I had just if I could only use two cements, I pick a good dual cure resin cement and I would pick a good general all purpose resin modified glass cinema. And there's really no need for anything else in both of those products. Both of those types of cements have plenty of evidence behind them anecdotal evidence and scientific evidence to support their use. So remember, resin cements could be auto cure like the old fashioned. Was the name I just mentioned. I don't know why. Right. That's right. All right. So it could be auto cure. Could be only like cure, which is only good for. Translucent veneers. And it could be dual cure. And this is really the one that I want to talk about. Next would be the next slide show that we're not going to get to our finish up this week. So resin cements have the best mechanical properties by far. So they are the hardest of all the cements. And they're the strongest of all the cements okay. So th