The Capabilities of Multilayer Zirconia

IDT: Was the esthetic aspect just something you evaluated subjectively, or was there some sort of specific technological advancement?

JM: I tell everybody: Not all zirconia is created equal. All the major players work hard on creating the best formulations; they perform extensive internal testing on shades. The gradient and how they blend it is very important. However, the most important question is: When you mill it out, does it look like A1 to you? Does it look like A2? The ultimate test for the laboratory is when it goes to the clinician and the patient. When you do these cases and start to receive positive feedback, that is when you know you have the right materials. Dentists should not be able to tell that the restoration is not layered. When you are using zirconia for indications such as single centrals and you are getting perfect, world-class esthetics and shade matching, that is when you know. Depending on the manufacturer, the amount of translucency, incisal material, and gradient can vary, but the key is to find the one that you like that provides the look you need.

IDT: Which strength specifications are most important?

JM: Flexural strength is the main one, but even that is not as important today as it used to be because most leading zirconias on the market are very strong. There is still so much misinformation-mainly on the clinical side-about 5Y zirconia, which was known to have less strength than 4Y and 3Y zirconia due to the higher yttria content. Our laboratory almost exclusively uses 4Y and 5Y zirconia. The 5Y classification scares many clinicians who have not kept up with the advancements in the materials, because when it was introduced to dentistry, 5Y zirconia was very brittle. It would break in the mouth and even in the laboratory. The manufacturers went back to the drawing board, though, and figured out that the brittleness was due to the manufacturing process. They all changed the way that they manufacture and process 5Y zirconia, and we saw a jump in strength. Now, most of our super-translucent multilayer zirconias are 5Y and they are within the 750-MPa to 850-MPa range. We no longer see brittle 5Y zirconias in the 500-MPa range, but many clinicians do not realize that. I recently worked with a clinician who had no idea 5Y zirconia was strong enough to be indicated for use in three-unit bridges, and it is. Talking with your clinicians and keeping them educated on the advancements of the materials you are using is so important.

IDT: What are the keys to using multilayer zirconia correctly and getting the best esthetic results? Is it all about nesting?

JM: Nesting is definitely important, but I do not give it as much weight as most people do. I believe the key is using the right zirconia for you esthetically, and then using support products such as liquid ceramics to really get the most out of the restoration. You can spend all day trying to perfectly nest a puck full of restorations with the perfect amount of incisal and the perfect amount of dentin, but that is not efficient. Often, we pick the zirconia based on the value we need, even for a single central. One of our zirconias is more opaque and brighter, while the other has higher translucency, which lowers the value in some instances. We have done single centrals with the more opaque one that match perfectly because we chose it based on value.

IDT: Do your zirconia restorations get bonded?

JM: We fabricate a large volume of zirconia single-wing Maryland bridges and zirconia veneers. By definition, zirconia cannot be bonded the way lithium disilicate can be bonded to a tooth. It is different. But that does not mean it cannot be done. Several researchers have published fantastic results, but the protocol I suggest reading about and recommending to clinicians for zirconia veneers or even regular full-coverage restorations is the APC technique from Markus B. Blatz, DMD, PhD. I find that this is absolutely bulletproof. In the early days of zirconia in dentistry, there were some issues with restorations staying cemented in the mouth; it was not uncommon, especially in the posterior region. Now, with advancements in materials and techniques like the APC, those problems are almost nonexistent.

(Editor's note: Read about the APC concept in this month's issue of Inside Dentistry at insidedentistry.net)

IDT: You've mentioned crowns, bridges, and veneers-what else are you using zirconia for?

JM: Everything. You would be hard-pressed to find a case that cannot be restored in zirconia. Everything in our laboratory across our four locations is manufactured with multilayer zirconia, except for the occasional PFM by request. We do crowns to partials in monolithic multilayered zirconia. We do hybrids in monolithic multilayer zirconia. We use it for regular, bread-and-butter work such as crown and bridge, single centrals, and anterior esthetic cases. I tell everybody, if you do not have enough room for zirconia, you do not have enough room for anything else. The only outlier in that argument would be a metal occlusal, but those cases are super rare.

IDT: What about situations when a dentist requests lithium disilicate? What is your pitch for zirconia?

JM: That conversation starts with your relationship with your clinicians. It's the trust and the respect you have for each other. The conversation might start with, "We do not do lithium disilicate." Right away, that shocks the dentist, but we follow it up with, "This is why." You need to be well-versed in the materials you are discussing. You cannot go into the conversation saying, "We do not do lithium disilicate veneers because we think zirconia is better." Remember, we are professionals, and we are talking to other professionals. You need to be prepared with literature and knowledge, so when you have that conversation, it is coming from a very educated standpoint. The clinician will respect that. One question that comes up when talking about zirconia veneers is, "How will I bond it effectively?" Well, let me point you in the right direction. Let me show you this paper, this literature, this research done by respected clinicians, and then we can talk about our experiences. "We have done these with many clinicians who are achieving excellent results." The conversation comes down to you saying, "I have a material that is as esthetic, if not more esthetic; that can be monolithic and has double the strength; and that has a bonding technique for it." When you start having a higher-level conversation, it puts your clinician at ease, and they are more apt to adopt what you are recommending. But you need to believe what you are saying. If you think zirconia veneers are awful, that will be evident in your conversation and your clinician will not want them. You need to believe in the products and materials you are using, and you need to believe in your work. If you are confident and prepared, then those conversations are easily had.

IDT: Are there any developments you want or expect to see in the next few years regarding zirconia?

JM: I think we will see some variations and some different blends, but I do not think it will be anything game-changing until we are able to 3D print zirconia effectively. I have used a zirconia printer, and I was not necessarily thrilled with the results, for many reasons. When you are evaluating something, it needs to be as good as or better than wherever the industry standard currently is. For laboratories, subtractive technology has proven to be wasteful, time-consuming, expensive, and inefficient; we all know the benefits of additive technology, but the materials need to catch up. We still mill today because we need to mill. But I would suspect that on the horizon someday, we will see a printed zirconia. It would be fantastic to be able to print it layered to shade. And maybe it is not even zirconia, but another material that shares the same properties of strength and esthetics that can be easily produced by laboratories. Right now, zirconia has advanced so far, and it is not a perfect material by any means, but I believe it is by far the best restorative material we have ever had.