Comparative Properties of Dental Restorations

Ladies and gentlemen, our next presenter is from Brazil, and no, he doesn’t have any spare tickets for the World Cup. Dr. Estevam Bonfante from Sao Paulo is a researcher of outstanding ability. He is here to give you the basis for a lot of the things that you’ve heard from Vin Morgan. His PhD, he comes from a dental family with father, mother, sister, and Uncle Tom Cobley and all, and I would like him to approach the podium. Thank you. Well, good morning. It’s a great honor to be here. I come from the University of Sao Paulo in Bauru, Brazil, where I teach at the Department of Prosthodontics. As you may notice from the slide, it says, Dr. Estevam Bonfante et al, so I do not speak for myself. I speak on behalf of a large group, which I’m very proud to work for. And why lecture on comparative properties of dental restorations in an implant meeting? Well, simply because it’s important to understand the clinical outcomes for tooth supported reconstructions in order to gain knowledge on implant supported prosthesis. And in addition to acknowledging the differences between the type of support, we must also distinguish where the prosthesis will be located. Is it an anterior or is it a posterior prosthesis? And what type is it? Is it a crown? Is it a fixed partial denture? Or is it a full arch? And lastly, and extremely important, as we shall see today, the material used to fabricate the prosthesis. And this is especially important in the all ceramic world. So just to give you an example, this is the mechanical failure rates of a variety of all ceramic materials, and we’re just generically speaking about them. We see that the mechanical failure rates, they increase towards the posterior region. So it is in the average of three percent in the incisor region, seven percent in bicuspid, and twenty one percent in the molar region. So there’s a clear increase in problems as we go towards the posterior region. So are we going to concentrate on the aesthetic zone or on the bicuspid region? No. Definitely not, because that’s not where the problems are. So just to give you an example of the combination of tooth supported crowns and the clinical outcomes with different materials, and let’s say, metal ceramic and all ceramic, and why are we speaking about metal ceramics here? Because we have to acknowledge that they are our gold standard. They’ve been in use this year for fifty two years. So, let us see how they what is the clinical outcomes according to this systematic review. In the anterior region, we see that if we use a metal ceramic or any given all ceramic material, the performance should be okay within five years. But when we go to the posterior region, there’s a clear difference, and we see that only the behavior of reinforced glass ceramics and those of densely sintered alumina can be comparable to those of metal ceramics. Okay? In terms of clinical outcomes and survival rates. And does that include zirconia? No. It doesn’t. Okay? And remember, we’re on tooth supported reconstructions. So now let’s go to zirconia. It’s a it’s a extremely important material. We know that of all the all ceramic materials, it’s the strongest one. And here are the outcomes for implant supported crowns, and this is pretty much all that is out there in terms of clinical studies. So, we see a study from two thousand and twelve, the follow-up period of two years. Here’s the outcomes of in terms of porcelain chipping. Twenty four point five percent for zirconia. Nine point five percent for metal ceramics. Another study from the same year, on a longer follow-up, three years, four percent of porcelain chipping in zirconia, none for metal ceramic. Another one, six months, seven point five percent for zirconia porcelain chipping. Now, this is the longest one that we have. It has just recently been published in the clinical implant dentistry and related research journal. The five years follow-up, it shows a forty two point eight percent of porcelain chipping. So, what I want to highlight here is not really how unhappy the patient will be with a fractured crown that has just been recently installed, but most importantly is the huge variability that we have in clinical outcomes. And I bet you may wonder that this is due to the use of different zirconia systems. And believe it or not, there’s just one main zirconia supplier in the world. Of course, they’re different differently manipulated by the different companies. But there are other problems involved in terms of handling and so forth. So it’s not as easy as that. It’s strong. Though we know that the framework rarely fractures, but we’re seeing an amount of complications which are just unacceptable. So, if one asks today, what is the state of the art of all ceramic materials for implant dentistry? We must acknowledge we have problems to solve. Alright? So we’re going to concentrate here this lecture on the hierarchical testing going from the least to the most complex geometries, Going from crowns to fixed partial dentures, and lastly, on full arch reconstructions, on all different kinds of materials that we can think of for using prosthodontics. We’re going to characterize these materials with a relevant fatigue testing method. And how relevant can it be? Well, we’ll see if it simulates the failures that we observed clinically. And this was done a while ago. It was developed at the Department of Biomaterials and Biomimetics at NYU. And I’m not going over too much detail on it, but we use sliding fatigue testing in the accelerated life testing method. But in essence, what does it do? We have an indenter that contacts a cusp incline, for example. It applies the load. It slides zero point three to zero point five millimeters, and then lifts off the sample without causing it any impact, just as it does in occlusion. These are some of the failure modes that have been observed in the clinics, compared to some that were produced in this laboratory. So, this was published five years ago, and everything that we’re describing from now on will have been performed using this testing methodology. So, as we said, metal ceramics, yes, it is our gold standard. And we when we first characterized it, you’ll be seeing this graph several times. Just be concerned about the horizontal axis, which shows the fatigue strength of the materials. And here, we are in molar crowns. Okay? So we see that the fatigue strength of metal ceramics, it’s over a thousand newtons. And let us see where zirconia is in this scenario. It is performing significantly lower in terms of fatigue strength, and this was also published a few years ago. And when you see these contours, when they do not overlap, it means that they’re significantly different. Okay? Can we improve zirconia? We certainly can. And I’m not saying that this is the best framework design that we could use, but it is clear that we must change the framework design. This is just an empirical framework design. We’re just bringing knowledge from metal ceramics to all ceramic world. And as you can see, what it has is just a lingual collar connecting to proximal struts, so it further improves the porcelain support. Do we really need porcelain support? Oh, yes, we do. If we don’t tell the CAD/CAM machine, this is the default coping that we may have, regardless of material that we’re milling. So it is an even thickness coping. We propose to modify it because if you see a cross section of a porcelain fused to anything crown, we see that at the end, the technician, he will layer, he’ll do the porcelain layering for aesthetics and function. And, at the end, we may end up with a huge discrepancy in porcelain thickness that we will never know, as you can see from these slides. You see, are having an even thickness in the buccal, which is, close to one millimeter. We’re we’re having two point one in the lingual. So is this a good scenario? Not for porcelain. Okay? So compared to uneven thickness coping, can we further improve it? Yes. We can, but yet, we’re far away from metal ceramics. Okay? So now, if the problem is porcelain chipping, let us completely remove the porcelain. We have materials out there that we can use it as a monolithic material. As you can see, lithium disilicate, e.max, to let us see what’s the performance of e.max, for example, in a two millimeter occlusal thickness. Okay. We see that its fatigue strength, it’s even higher than metal ceramic. That’s great. But we do not always have that amount of occlusal clearance. Let’s say that we have one millimeter, it still performs quite well. So, from this graph, which pretty much has characterized most of the relevant materials that are out there for when we’re using porcelain, porcelain veneered reconstructions. We see that, yes, we have materials that can perform as well as, or even outperform the fatigue strength of metal ceramics. But now for implants, there are a few other things that I would like to invite you to reflect about them with me. Okay? So one of them is that composite crowns, they have been shown to be better able to absorb shock from occlusal forces than crowns made of metal ceramic. And this seems to have an impact in bone, an important one. So it has been shown that ceramic crowns transfers higher stresses to the abutment and bone implant interface than composite crowns. And now when we rank the materials, when materials have been ranked for shock absorption capacity, we see that composite and above all acrylic resin crowns are more able to absorb shock from occlusal forces than crowns made of zirconia, ceramic materials, or even gold alloy that we know that it does present some ductility. So another thing, and a very important aspect that we cannot forget, and this directly applies to implant dentistry, is that a patient wearing an implant supported prosthesis, he presents a substantial loss of proprioception, okay, and a reduced tactile sensitivity. And that ultimately results in a decreased masticatory muscle coordination, and therefore an increasing susceptibility to occlusal overload. So that is why some patients wearing an implant supported prosthesis, they may be more prone to producing failures on their own restorations than patients wearing a conventional tooth supported prosthesis. So, now if we look back at the guidelines for reconstructions back in the early days of osseointegration, there was probably a gap in the course of evolution of prosthodontics, especially for implant dentistry. So, you’re all familiar with this publication. It’s a seminal publication from Brånemark, where he stated back then that although empirically, because we didn’t know all this, that artificial teeth made of acrylic resin tended to compensate for the resilience of the PDL. Maybe we should look back, and I’m not saying, I’m not even suggesting that we should go back to use the same composites that were used in the 80s. But what I’m inviting you to is to have an open mind and to acknowledge all the advances that have been especially in the polymer chemistry engineering. So, we have composites that are completely different from the ones back in the eighties. And for those of you who hate the word composite and cannot even think of it for any type of restoration, of final or definite restoration, you’ll be happy with this slide that Doctor. Morgan just showed you. So according to the latest code on dental procedures and nomenclature from the ADA, they say that porcelain ceramic, they’re defined as a pressed, fired, polished, or milled materials containing predominantly, Okay? Inorganic refractory compounds, and that including porcelains, glasses, ceramics, and glass ceramics. So note that the word predominantly changes everything here. So, that means that you can have some amount of organic matrix and some ceramics embedding in that, and it’ll be called porcelain or ceramic. But controversies aside between material science definition of porcelain, ceramic, and the ADA code, let’s go to what really matters to us. Okay? The IACs, and what are the questions that the clinicians would like to have answered if they are to use, or if they are willing to use composites for implant supported reconstructions. One of the questions that we thought of is how good is the bond between the composites and titanium. It has to be a strong bond in order to withstand occlusal forces, especially in the molar region. Strength? That’s an obvious question. Aesthetics. Why aesthetics? Because composites stain, don’t they? Alright. So, going to the very first question, I’m not going to spend much time over this, since as long as you sandblast an abutment, and you apply any type of metal primer, you can have sufficiently high bond strength. And not only in the immediately, but in the long term, as we have shown a few years ago. So we’re good with bond. Let’s move on to our second question. So this was a funny study that we did a few years ago too, where we compared several composites as used as IACs for molar crowns. We compared them to PFM. Okay? To porcelain fused to metal. But, back then, we only did single load to fracture testing. And as you can all see from these numbers, we have we have seen that all the composites presented strength as high as porcelain fused metal. And we have to acknowledge that a single load to fracture testing is not meaningful type of methodology to show anything. It doesn’t mean much. Believe it or not, this was one of the most important data sets that we have ever collected. And I’ll tell you why. From this study, where you see the loads to failure above a thousand newtons, we have learned that if we were to test composite materials for fatigue in regular screwed systems, we knew that the abutment systems abutment, their screws, or even the implants, they would actually fail even before the composite materials. So just to give you an example, half a dozen example out of our over twenty publications on the topic where we have investigated, for example, the effect of implant abutment connection designs, external hex, internal hex, internal conical connections, or what is the effect or the difference between screwing or cementing a crown over an implant, differences between platform switching and matching platform implants, and the combination of all of these. In all of these studies during fatigue, we have observed that the implant components, they usually fail at loads below four hundred newtons. Okay? So, just to give you an example of one of the strongest connections because they’re all internally connected, here are the failure loads. They’re all below four hundred newtons. So can we test composites on them? We certainly cannot. So and as we see, what are the relevant forces in the mouth? These are just examples of maximum voluntary bite forces, and and we know that patients don’t do that every day. But, just to give you an idea, and let’s go to bilateral because they’re more relevant, in female, they’re already above four hundred Newtons. In males, they can be over a thousand Newtons. Let’s put it as a relevant average six hundred Newtons. So, this slide may explain why dentists perhaps they feel more confident when they splint adjacent molars, for example, in regular screwed systems. Because in maximum voluntary biting forces, or even in functional forces, they could be able to fracture the screw or the abutments, and so forth. So we’ve learned that materials such as composites should be tested under fatigue on simplified implant abutment connections. So we cannot have screws. We need a solid abutment, a monolithic abutment, just as you see, just as the the locking taper because the screw retained components would fail before the composite materials. So this is the very first fatigue study that was performed by doctor Suzuki from Tufts University. And back then, he evaluated just two composites that were commonly used, diamond crown and ceramage, and he showed that the fatigue strength for both of them, they were not significantly different, as you can see from the overlap between the contours, and they were in the average of eight hundred newtons. An interesting finding from that study was that when we had a failure, it was usually a small composite chip that, by repolishing, we could return the crown to function, if that was a real crown in a patient. Or, if it were a little larger, the chunk of composite, it could be repaired for function, and be returned to function instead of crown being replaced. But now, one thing that we have always questioned because sometimes we have to acknowledge that there’s just a huge chunk of composite onto the abutments. And if we bring the knowledge from porcelain, we see that that would never be feasible for us. That would never be applicable for any porcelain based restoration. So the question is, do composites need support, or how much support do they need? We have designed this study where we had three different abutment designs. One that we called large base, where you had a six point four millimeter base, and the other ones, there are small base with a five point two diameter. And we had a four millimeter cone in the center just for composite retention. And we also wanted to see if we reduce that to two millimeters, where you would end up. This is just a cross section of the crowns, so you have an idea of the heresy that it is. If we think of this concept for porcelain, of course, we could never have this amount of porcelain unsupported, as you’ve seen previously. So, that’s the large base, a small base with a four millimeter cone in the center for composite retention, and the two millimeter. So our findings were that with a large base, it’s fatigue strength. It’s close to eight hundred newtons. Nothing new to what we have seen before. And compared to the small base with that tiny little post for composite retention, there is a significant decrease in strength, but yet, still, we’re in the six hundred newton average. And how are the failure modes in that tiny cone in the center? It was usually a crown debonding. We didn’t have, like, an actual failure. But then when we used the same cone height, okay, for composite for composite retention but in a reduced base, we had a fatigue strength similar to the large base. Answering the question, Do they need support? Actually, not. And this study was the basis for the development of the universal abutment that you’ve just seen in the presentation of Doctor. Morgan. One of the things that we’ve been realizing, we do fractography in every single study, is that while you’re packing a material, let’s say an indirect composite onto abutment, we always ended up inserting some voids during packing. And this is true for a technician who is hand layering a porcelain, will always find some defects, flaws, voids, bubbles, and so forth. And it is also true for pressed porcelain, as we have seen. So can we even improve the material’s overall strength if we mill them from a CAD block from a CAD/CAM block, where we’re having the material being more homogeneous. Well, let’s see. We have investigated that, and we have compared the indirect composites that you’ve seen with a resin nano ceramic material. Brand name is Lava Ultimate from 3M ESPE, and, of course, with our gold standard, which is metal ceramic. And we have found that, yes, there is a difference. You can get a substantial increase in fatigue strength. And we have been realizing that this is true for other materials as well, when they’re coming from CAD/CAM, and we’re using them as IACs. Interestingly, both of these materials, they’re not significantly different in terms of fatigue strength from metal ceramics. So this clearly shows that, yes, we’re on the safe side. So, just as a clinical significance comment here, as we think of repair, these are some of the failure modes. So, on the left hand side, you see an indirect composite, or it could be a CAD/CAM block failed, and on the right hand side, you see a metal ceramic failed. So, clinically, which one would be easier to repair? Well, for an indirect composite, all you need is a hydrophobic adhesive and just pack some composite onto it. For a metal ceramic, what you need is metal primer on the exposed abutment, hydrofluoric acid etching, silane, plus the composite. And, we’re commonly saying that there’s a huge advantage in composite repair, and we have no idea, until not long ago, what is the strength of a repaired composite. So, this was an interesting study that we have recently done. And one of the things that when we think of a block for a CAD/CAM, we have technology that, yes, we can get an acceptable aesthetics, but the blocks themselves, they’re monochromatic. So until the companies develop different shades within a block with different degrees of translucency, we’re sort of limited in terms of aesthetics. Can we improve that somehow? Yes. We can. We can, we could add a layer of direct or indirect composite onto an undermilled CAD/CAM block. Okay? So obvious questions. How strong is the bond between the CAD/CAM composite and a direct or an indirect composite. And, obviously, what is the strength of a repaired crown? So, in terms of bond strength, we have performed the micro tensile bond strength testing, and we have found that the bond strengths, whether you’re using Ceramage, an indirect composite material, or Filtek Supreme, the bond strengths, they’re high enough to withstand occlusal forces. Now, moving on to the repair study, we’ve developed a method to standardize cusp removal and to replace it back with either direct or indirect composite. In this case, the same composite that we used for bond strength testing, ceramage and Filtek Supreme. This is the inherent material. You have already seen this plot. To our surprise, when we used a direct composite material, like Filtek Supreme, yes, there is a decrease in strength, but still, we’re in the same average of fatigue strength of metal ceramics. But most surprisingly is that when you use an indirect composite material on the top of a CAD/CAM block, we go back to the same original strength of the inherent material. So there’s no loss in strength. So is repairing composites a safe procedure? Yes, it is. And most interesting, this really fun to see. The fracture that we have observed in fractography, it never occurred at the bonded interface. It was always cohesive within the composite. Okay, so then we answer the second question regarding strength. Going to the third question, which we’re also not going to spend much time over this, because you see from clinical examples, several composites being used over five or ten years. But just to show you some scientific study of composites that were aged and subjected to staining in coffee and wine. Okay? That’s the most aggressive type of staining that could be in a composite. So these authors, they have found that staining is superficial, only twenty microns of the surface. So original composite color can be reestablished by polishing. This is nothing new to Bicon users and who does IACs probably know that this is totally doable. So we’re good with aesthetics too. And as doctor Morgan said, this could even be called, yes, why not? Ideal telescopic crown. Not only you do not use a cement, you do not need a cement, but the crown is still retrievable. So, moving on to our second scenario, which is implant supported for fixed partial dentures. Let’s take a look at the clinical outcomes and the literature that we have for the different materials. We will go straight for the strongest ones, which is zirconia. So, this is study which is a prospective cohort of five years. It’s the same study that I showed for crowns, which showed a forty two point eight percent of porcelain chipping in crowns. When it comes to bridges, they have found sixty two percent of porcelain chipping in five years. Okay? And another study where they have evaluated two different systems, zirconia systems, they have found seventeen to sixty nine percent of porcelain chipping also in five years. That’s pretty much the same scenario that we have seen for zirconia supported crowns over implants. So this, for us, it definitely raises a red flag and calls for alternative materials. And when we talk about fiber reinforced composites, why? Well, because they present a unique high stiffness to weight and strength to weight ratios. What does it mean? It means that they’re light, yet they can be very strong. If we look around, fiber reinforced composites, they are everywhere. Alright? From the aerospace to aeronautical fields, and biomedical applications include artificial tendons, ligaments, intervertebral discs, hip stems, and so forth. When used as an implant supported restoration, it has been shown in finite element analysis that implant supported fiber reinforced composites when compared to metal ceramics. They could eliminate the excessive stresses in the bone implant interface and maintain normal physiological loading of the surrounding bone, and therefore minimizing the risk of peri implant bone loss. The same scenario that we have seen for crowns. So, this motivated us to further drop a few questions regarding the use of TRINIA. So, one of them is how strong is the bond between TRINIA and adhesive cement or most importantly, is the adhesion like between TRINIA and Ceramage. So, in this case, we have evaluated also in micro tensile testing the bond strength using just the hydrophobic Ceraresin Bond from Shofu, in either sandblasted or no sandblasted TRINIA. Our findings were that bond strengths were high for either group, but there was a significantly higher bond strength when we sandblasted. Do we really need that much of strength? Of course, need, and we do recommend sandblasting. Although the difference is not that much, if we see the numbers, it’s forty one as opposed to thirty six to a non sandblasted TRINIA surface. But yes, it will be nice to sandblast them prior to composite veneering. To our second question, regarding the performance of materials for implant supported reconstructions used as fixed partial dentures, we have basically compared metal ceramics to pretty much everything that is out there. And that includes in every material, in every bridge that has a substructure, we have used a twelve square millimeter connection. So we have compared metal ceramic to TRINIA, also on a twelve square millimeters veneered with composite, solid composite bridge, okay, no framework whatsoever, and zirconia veneered, also on a twelve square millimeters. And additionally to that, we have evaluated and I know this sounds like heresy, but we did it we have evaluated a TRINIA framework of three square millimeter area connector. That means three millimeters height by one millimeter width, in addition to this group. So there are five groups here. This is a cross section, you have an idea what it looked like. The solid composite and that is the twelve square millimeters bridge. This is what everyone would conventionally use. We know that for all ceramic materials, the minimum that we can use for zirconia is nine square millimeters. And let’s see how it all behaved. In terms of probability of survival, TRINIA on a twelve square millimeter had the same probability of surviving that amount of cycles and loads as metal ceramics. And the same was true for the monolithic composite. Okay? And the only difference here in terms of failure mode is that failures in the monolithic composite, they were catastrophic. There was no chance for repair. Zirconia, the same framework design and area, presented a significantly lower probability of survival compared to metal ceramic and to TRINIA. There was a drop, of course, in probability of survival when we went to that tiny connector in TRINIA. And it was similar to zirconia in the twelve square millimeters, although in higher numbers. Okay, seventy nine percent as we see, as opposed to fifty five percent for zirconia. So, in terms of strength, if we put all of them in this chart, going from our gold standard, metal ceramics on a twelve square millimeter, we see that TRINIA is not significantly different from them nor is the monolithic composite. Not surprisingly, if we reduce the connector dimension to a three square millimeter, and that’s a real worst case scenario, That decrease in strength, significant decrease, only happens due to prosthesis flexing during loading. But when we put zirconia in the chart, it is not significantly different from TRINIA with that tiny connector. Also, different in terms of strength from metal ceramic. But, what is important to see here is that zirconia is down on the graph because it presents a llow Weibull modulus, which indicates a wide variability in results and scattering data. As conclusions, we see that the failure modes, they all allowed repair except for the monolithic composite bridge, Fractures were obviously larger in the three square millimeter due to prosthesis flexing when compared to TRINIA twelve square millimeters. But even in that group with that tiny connector, we did not find a single framework fracture, which was quite interesting and it was a big surprise to us. The probability of survival for any composite bridge in the twelve square millimeter dimension they were not significantly different compared to metal ceramics, except for zirconia, which was significantly lower. Now, going to the very last scenario, which is full arch prosthesis. This is an example of a TRINIA four on short. And how are we going to test that in the lab? Well, it’s quite a challenge, and the best that we can do is to maybe divide that and split that in half and test that as a cantilever. So, we designed them. We thought it was crazy back then to have a twenty millimeter span cantilever, so that means two molars. And we found out just yesterday that that was not maybe as crazy as we thought we could go. Yesterday, we were testing an even longer span, which I’m not telling you today because we’ll probably have all set of results in a couple months. But, a twenty millimeter span cantilever with three different framework designs. And let us see our findings. The only difference in the framework design here was the amount of composite that we had occlusal to the abutment. Okay. So, we either have had one millimeter, two millimeter, or three millimeters. And we applied the load in the most distal end of the cantilever. Of course, we needed to have some clearance to allow prosthesis flexing. Our finding was that there was such a huge amount of flexing before final failure that maybe from a clinical standpoint that wouldn’t be relevant because the prosthesis would be contacting the soft tissue prior to breakage. Clinically, what do we need? We need at least two millimeters on the top of the abutment. We haven’t really evaluated anything between one and two. We’ll be doing that soon. But, if you have two millimeters occlusal to the abutment, in that scenario of a twenty millimeter span cantilever, we can be on the safe side. As relevant finding, if we want to improve the strength of TRINIA, when used as a twenty millimeter cantilever framework, we must provide at least two millimeter occlusal thickness for each coping because that preserves the integrity of the fiber mesh continuity. So, this is what we’re looking for, and this is what we do want to avoid. We need fiber mesh continuity on the top of the abutments. So, if we think of all the framework design principles or that have been proposed for any porcelain veneered prosthesis, and we try to translate that to composites, they simply do not apply. Framework design principles for porcelain veneered reconstructions such as connector dimensions or anatomical support for veneering, they’re not relevant for TRINIA prostheses. So, we can have the answers for these questions in terms of performance. We must acknowledge that every decision that we make in the practice, they do have a role in the final longevity of the prosthesis. Most of these knowledge and most of these information is already out there in the literature. We see that some types of treatment planning, as, Let us do a full arch zirconia on an external hex implant, on screw root form short implants. Do you think they’re looking for trouble? I think so. As a take home message, when choosing a material for implant supported prosthesis, let us consider how easy it is to fabricate, adjust, repair, always remembering that implant supported reconstructions commonly demand more maintenance than tooth supported ones. High reliability. What do I mean by that? High probability of survival. Aesthetics and versatility, of course. I do acknowledge that it’s a massive amount of information, and much of it may sound like heresy, just as our group thought it was several years ago when we had started our own independent testing. But it is really clear to us now that we must have an open mind. Alright? So, as this German scientist who is known as the father of rocket science once said, One good test is worth a thousand expert opinions. And patients, they do not benefit from random opinions. They’re the ones who usually say, You’re the doctor. Go ahead and do whatever you think is best. So let us do our best. Thank you very much.