Zirconia & Cements: Optimizing Durability and Predictability

You're listening to The Dr. Phil Klein Dental Podcast Welcome to the show. I'm Dr. Phil Klein. Zirconia categories are specific to patient needs, and it's important to know what to use for a given patient and clinical application. Today we'll be discussing both zirconia and dental cements and how they contribute to durable and predictable results. Our guest is Dr. Daniel Poticny, who maintains a full-time private practice in Grand Prairie, Texas, and is an adjunct clinical professor at the University of Michigan School of Dentistry. He is a published author on digital dentistry, materials, cements, and adhesive dentistry, having presented internationally since 2005. He is a consultant and advisor to manufacturers, and serves as an editorial board reviewer for numerous dental journals. Before we get started, I'd like to mention that Dr. Poticny’s webinar titled Zirconia and Cements, Best Practices for Predictable Results is now available as an on-demand webinar on VivaLearning .com. Simply type in the search field Patikny, P-O-T-I-C-N-Y. If you're doing or considering doing zirconia in your practice and you want to get a better feel for the materials and the cements for these materials, I highly recommend watching this webinar. Dr. Poticny, it's a pleasure to have you on Dental Talk. Thank you, Phil. So we really appreciate your time. I know you're extremely busy, as many dentists are, and you're involved with education and so forth, so we're happy to have you on the show. So to begin this podcast, let me ask you this about zirconia. How are zirconias categorized these days, and what does it mean for a dentist's laboratory to understand this? You know, I think there's a lot of confusion out there about how do you typify zirconia and how do you apply it to your clinical practice? And there's a lot of, I think, confusion in terms of labs communicating to dentists exactly what they're using. More commonly, dentists, I think, associate... the use of zirconia with brand names, and there are, you know, an awful lot of them out there, and there are a lot of popular ones. You know, going back to the original one, you know, the one that most dentists are familiar with some 10 or 15 years ago. More importantly, I think a dentist needs to understand what the chemical composition or the composition of the material that they're using and how these things kind of relate to performance. Fortunately, there is a way of actually knowing if your lab will actually share this information with you. For instance, Currently, we have what we call 3Y, 4Y, and 5Y zirconias, and it relates to the amount of ytria, mole percentage of ytria that's incorporated into the material. The tertagonal phase is what typically is what is known as the strongest zirconias out there, and it's 100% tertagonal, and that would be the 3Y zirconia. On the other hand, the 5Ys are typically the cubic phase zirconias where they're a 50-50 mix. Consequently, their strength actually drops because they're a 50-50 mixture of the octagonal along with the cubic phase. And then, of course, now, later on, we have the four Y zirconias, which are the four mole percentage zirconias, and they're typically a 75% octagonal and a 25% cubic phase. And what we should know is that the stronger the material, you're going to get a decrease in translucence. But again, doctors are typically using zirconia for its strength properties. Now, there's also a lot of confusion related to flexural strength versus fracture toughness. And if you had to have one or understand one better over the other, I think fracture toughness is going to be the one you're going to typically count on more for clinical performance because it's actually a better indicator. Flexural strength is something doctors are all familiar with. They think the higher the flexural strength, the better. Well, in a way, that's actually true. So how do we kind of put all this together? Well, fortunately, there is a way that's being used and has been used perhaps the last five years and something you should talk to your lab about. It's called the ISO standards. And the ISO standards, it's an international organization that uses uniform methodology to help. in our case, to help doctors understand how a material like a class 2 material, a class 3 material, 4 and 5, and so on, can relate to clinical applications. For instance, a class 2 ISO standard would be used for a single unit. It easily plays cementation. I'm talking about ceramics now is what I'm talking about. And typically, these are going to be in a range of 100 to 300 megapascals. An example for this would be our typical glass silicate restorations that we have used for years that are typically bonded to the tooth. The Class III materials can be used as single units or three-unit anterior bridges, typically in the range of 100 to 500 megapascals. Something like this would be commonly known as a material such as lithium disilicate, which is wildly popular for dentists and is actually being somewhat supplanted by zirconia now as doctors tend to relate. tend to prefer something that is actually what they call bulletproof. Then there's the class four materials, and these can be used as three-unit anterior or posterior situations, and they range from 500 to 800 megapascals. Now, there are some exceptions to those because some of the four Ys actually exceed those parameters. And of course, the class fives are the materials that are used, that doctors typifies the three Y zirconias, which exceed 800 megapascals in strength. Now, i've been talking about flexural strength and if you were to ask your lab what class material are we using for the zirconia that you're supplying to me rather than the brand name they should know the answer to that this is how you're going to want to typify these things because the class 5 zirconias are typically going to have a fracture toughness uh well in excess of the strength that would actually be required for clinical performance so i think you should use these ISO standards universally rather than talking about how much flexural strength you have. Fracture toughness is going to be related in the ISO standards here that I'll talk about here a little bit when we get into the category of talking about strength versus aesthetics. For the general dentist that goes to work every day that has a million things to worry about and lots of different procedures they're doing, they should have a lab where the doctor would explain to them which tooth it is, they should have an understanding of the occlusion. The occlusion obviously is going to be the factor that's critical towards long-term success on most of these CAD-CAM materials, I would assume. The lab would say you should be using this particular class material, this ISO standard. That's a great way of, I mean, that's a good question because If I were to call a lab, and I've done this with laboratories, I'd say, I've got a three-unit bridge here, and I want to use something that's going to be a ceramic. What should I be using here? That material should be selected based on its class properties. On the other hand, if a doctor calls and says, I'd like a class four material for something that I'm using here, and this is where I call labs, and they're totally confused, they don't know the answer to that. They'll typically just say, well, it's X mega Pascal. So you have to know where these things kind of fit in. And you can find these charts anywhere that shows the relationship of these things. And I think if doctors understand this a little bit better and they understand how, you know, aesthetics and strength work together, I think it's a lot easier for both the lab and the dentist to communicate with each other. Right. So you mentioned how aesthetics and strength work together. So I'm assuming based on what you just described and what I know already is that as you move from class two to class three and up the ladder, you're getting greater strength, but your aesthetic considerations are being slightly compromised, right? How does that work with a general dentist who's trying to achieve aesthetics and strength with zirconia? Well, you can't have your cake and eat it too, as they say. All right. But there are some, you know, actually some workarounds on those things. So, for instance, the three wide zirconias, which are the strongest and toughest, have 100% retagonal phase. And they break up light as it passes, tries to pass through it, which is why it looks relatively opaque. The cubic phase looks actually better, okay, because it lets light pass through on a more even or linear basis. So it has a more natural appearance. Now, if you think about that just for a minute, and this has always been true with silicate restorations, it's always said the more glass content, the more attractive the material is. And this is actually what you're talking about over here. So, for instance, in a 50-50 proposition, you would not want to be using a material like this typically on a molar. On a 3Y, though, you're not going to typically be wanting to use this on a canine or an incisor either, okay, for the obvious reasons that, you know, you're going to. It's going to look very dull. It's not going to look very attractive in a patient's mouth. So it kind of gets to the point where four Ys maybe kind of fit into these things because it's actually a little bit better blend where you get a nice balance of the strength. On the other hand, you get a decent amount of aesthetics with it that give you just a little bit more flexibility. You know, I'd make the statement that sometimes strength is overused because we've had tremendous success with, for instance, lithium disilicate restorations over the years, and they've done actually quite well. And they tend to fall in a category known as the class three. But, you know, they can't be used for things like fixed partial dentures, those types of things, three and four unit types of things. so you know for that reason i think that it's a more a balanced approach everything's a trade-off you know everything you got to look at your patient what's the patient's needs like for instance if i got a bruster and it's a second molar i'm going to use a 3y i have no reason uh i can i can make it so when a patient opens their mouth they're not going to be embarrassed but if you look at it with uh you know through a magnet you know through loops You know, you look at it real close and you're going to blow it up, you know, on a monitor. Well, it's never going to look as attractive. But the more important thing here is function and something that's not going to embarrass a patient, typically known as a gold crown today. To me, a 4Y fits a nice niche because you can actually use those materials, what I believe, from a premolar back to a first molar type situation. I'm sold on 3Ys for the molars. but i think the four wives fit a niche and that's my point now on the other hand when you get to the anteriors you're talking in the social six canine to canine i'm not probably going to use either one of those for a patient unless for instance i've got a 65 year old patient you know they've got uh some really dark teeth or monochromatic those things might actually work but That said, as a general statement, the answer would be no to that. So it's understanding how strength and aesthetics need to be balanced on the location in the mouth. Yeah, totally makes sense. So what is necessary to achieve adhesion to zirconia? Because we hear all about that all the time. Can you bond to zirconia? What's the best way to get it to stay on the tooth where we don't have any problems getting a phone call in the middle of the night saying that the crown came off? And of course, that goes along with, and I'd like to... to address this as well regarding conventional looting cements versus pairing zirconia cementation with adhesive cements? I've been using zirconia for a very long time, you know, actually since it first came out. And it really relates to what doctors are kind of reporting out there in the field. I don't have, I'm not bragging, but I just generally don't have an issue with things staying in place and with things breaking. Although... is enough of this reported in the field because dentists have this idea that it's a bulletproof material why am i you know why am i still having problems and also because zirconia is relatively new to dentistry although it's wildly popular now there's concern that the long-term bonds of cements to the zirconia interface by itself is not durable Now, I'm not certain that we have enough information at this point in time. I think caution is still advised. But if you think about it, zirconia can also be conventionally cemented. It doesn't always have to be bonded, which we'll talk about here in a minute. You know, zirconia has no glass content. And because it has no contact, unlike a porcelain, it can't be etched. And if it can't be etched, you can't get that micromechanical retention with the addition of silane that will actually create a bonding effect like you can get with glass ceramics. Other issues come into play because zirconia, if you're going to try to bond or zirconia, zirconia is a crystal. And in the absence of glass, you're going to depend on a chemical bond with no micromechanical retention possible. Saliva can contaminate the intaglio surface of zirconia, and it can defeat the bonding attempt by doctors. So for that reason, zirconia needs to be clean on the intaglio. There are a variety of different ways of making it clean. Cleaning pastes are very popular today. The cleaning paste could be applied to the intaglio, left in contact for 20 seconds to a minute or so, rinsed off, and that will eliminate the phosphate or the effect of saliva on the bond or the chemical bond to the zirconia surface itself. Bleach is also very effective. It's certainly less expensive. It can be a little messy if you get it on a black scrub. But, you know, that said, bleach is also effective. My favorite way of doing this, and I think anyone that handles zirconia or porcelains of any type in clinical practice, they should have some level of air abrasion available to them. Typically, you could use 50 microns of aluminum oxide. pressure lower than two bar, and you can clean the surface. It will eliminate the phosphates, and it's also believed that it energizes the surface of the intaglio of zirconia to make it more receptive to the MDP primer, which is the necessary component to achieve a chemical adhesion to the intaglio. and it must be MDP. Now, MDP can be used as a separate primer, and it can also be incorporated into a variety of the universal adhesives that are out there today, which also contain MDP. I can't vouch for one over the other. I tend to use the universal adhesives, and I had tremendous success with it ever since the first one came out back in 2014. Just out of curiosity, what are you currently using in your office as far as adhesion and cements? I like to keep things simple. The fewer the steps, and assuming everybody reads the instruction, the better. I like products with known support, with reputation, products that are proven to work, both through the manufacturer's testing and through independent testing on both sides. Wouldn't it be great to have one product to do all your adhesion and one bottle to take care of all the chemicals that... i like the universal products i like to use 3ms universal self-adhesive resin cement which can be used and is compatible with their universal primer adhesive so if i want adhesive bond to zirconia or porcelains i can use the self-adhesive resin cement which contains silane and mdp you can do a one second tack cure it peels off in a gel state You can cure through the material, or you can wait for it to self-set. If you need superior adhesion, you can use the primer and adhesive with the self-adhesive resin cement, and they are compatible with each other. I use no other cements or no other bonding agent in my practice. End of story. No confusion with bottles, no confusion with mixing, simplified delivery, and a long-term track record. And that's really important is keeping inventory simplified and workflow simplified and not mixing materials from different manufacturers because then one manufacturer blames the other one and so forth. At least you can get the support from the company that you work with. And 3M, of course, has been in the business of adhesion for a long time. This podcast is telling our audience that you really have to have a broad understanding of all the nuances of... the preparation design, the occlusion, the materials, the aesthetic considerations, all these things have to come into play. And then you have to have a good laboratory that you can communicate with so they understand what you're looking for. And that plus good technique, isolation is going to give you what the title of this podcast is, which is durability and predictability. That's what we're trying to achieve. Thank you so much for your time. Thank you, Phil. Have a great day.