Predictable, Exceptional Esthetics with Durability
A Q&A With Pinhas Adar, CDT, MDT, Owner of Adar Dental Laboratory in Atlanta, Georgia
Inside Dental Technology (IDT): Why is zirconia such a useful material for full-arch restorations?
Pinhas Adar, CDT, MDT: When I started doing full-arch zirconia cases approximately 10 years ago, minimal layering was recommended. The restorations were beautiful if the technician was artistic. However, the very first dual-arch case I fabricated resulted in the patient chipping the ceramic 2 weeks later. I had charged approximately $60,000 for the case, so of course, I worked on it for free. I did not understand why it had chipped, but I debonded it, fixed the ceramics, polished the cement, and sent it back. A few weeks later, the patient chipped it again. I learned that ceramic on implant cases can fracture, regardless of how protective it is. That was a turning point because I wanted to help these patients, but it was not a good business model to be in the repair business when every piece eventually will break. They look beautiful, but I was not willing to pay that price. On the case that I mentioned, we remade it with monolithic zirconia. I knew I had to find a better way. I worked on developing a system that would be more duplicatable with a monolithic, strong material that would be biocompatible in the mouth. Research shows that the tissue responds well when zirconia is polished and treated well. Obviously, it should not be rough.
Still, there are also limitations for zirconia. It cannot be used for every case. If the planning is not done correctly—for example, if there are too many implants and too many holes—it creates a weaker product. That is not a product problem, but rather a planning and indication problem.
IDT: Are there particular types of zirconia you prefer to use for these cases?
Adar: When I experimented with different products, the outcomes did not look different esthetically. Anything can be made to look good with the human touch. The question is what is predictable and sustainable in the long-term, with a duplicatable process. Multilayer zirconia with multiple translucencies can be a very effective material, but it has some disadvantages; the angulation or positioning for screw-retained restorations is not always consistent, so the strength and translucency do not always end up in the correct place. I wanted a workflow that would be more predictable for every case, so I now use one color: white. It is high-strength at 1,250 MPa. I get the strength and predictability of milling, along with the predictability of coloring because of the system we developed. We provide clients with customized shade tabs that we fabricate using the same materials from which the final product will be made. The patient selects their preference from our five options: bleach, OM2, B1, A2, and C3. All of those shades start with the same white block, so the coloring technique is the same. Any of my technicians can replicate it, and there is no guesswork involved in trying to match to a different shade guide.
IDT: What are some of the other important considerations involved in getting the most out of zirconia on these cases?
Adar: Vision is the main requirement for any case, digital or analog. If you do not have vision, you do not know where you will end up, and nothing else matters. Digital tools are great because they allow us to scale our businesses, but what differentiates my laboratory from another laboratory that uses the same tools and the same zirconia is our vision and our abilities. That may be 20% of the whole workflow, but it is closer to 90% of the overall difference. Technology does not replace the human touch. It enhances the human experience. It allows us to do more. I can mill three full arches overnight, and the machine does not complain. But the post-processing—shaping and finishing—is the key. Each laboratory has its own protocols, obviously. Ours is very efficient. We used to do one full arch per week, and we have now scaled up to 24—that is mostly due to the speed of milling, but also because our post-processing protocol for coloring, adding pink ceramic, etc, is very efficient.
IDT: What are the other important considerations such as sintering and supports?
Adar: Many people talk about a completely digital workflow, which is modeless. That is a good concept for milling PMMA or 3D printing, but zirconia is a different product. Sintering makes a difference. Sometimes, it can warp the zirconia. Checking the fit on a model is critical. We also have figured out which types of cases are more prone to fit problems, and we avoid those. Regardless, however, sintering is a crucial part in our process. We have experienced issues with cracking when we used faster sintering protocols, so now we raise the heat very slowly and cool it very slowly, for a total of approximately 17 hours. Our newest oven can sinter nine arches simultaneously, so the longer sintering time is not a problem.
We also stopped utilizing the support for 99% of our cases. Sometimes it worked and sometimes it did not. Sometimes the bridge was snapping from the support. With a flashlight, we noticed small flaws in the supports, and sometimes the cases did not end up fitting as a result. Without the support, not only do we achieve better fits, but we also can often fit two arches in one block.
For some very complex cases, such as zygomatic implants with angles of screws coming out from the ears, it is better to have a metal bar and a secondary part, but we do not mill metal bars, so we do not do those cases.
IDT: Are there other contraindications for zirconia?
Adar: A lack of space is definitely a contraindication. I receive cases with 5 mm of vertical height, and the cylinder alone needs to be 6 mm. Metal would be a better option there, or else the dentist needs to open the vertical or reduce bone—which is typically not an option at the point when we receive the case. Physically, we could mill something for a 5-mm space, but it will break.
As I mentioned earlier, I have noticed that the more implants you have in zirconia—for example, 14 teeth and 10 implants—the weaker it may be because a thickness of at least 2 mm between each abutment is necessary for ideal strength. More holes also increases the likelihood that the milling may not be completely accurate. So, for those cases, I recommend either a different material or a substructure. A significant amount of space is necessary for a metal bar and a secondary zirconia structure, but the metal supports the zirconia from breaking. I know laboratories that do that successfully, and it looks nice.
IDT: Is zirconia ever too heavy a material?
Adar: I hear stories about that. However, a bridge is not held in our hands; it goes in the mouth. I have asked patients with some of the biggest bridges I have ever fabricated whether they felt heavy, and nobody has ever complained. They say it feels natural.
IDT: What about clicking noises with zirconia against zirconia?
Adar: I have heard that concern as well. I always tell patients that zirconia has a certain feel and sound. When you prepare the patient for that up front, there is typically no issue. I tell them it will be the most biocompatible material, it does not smell, and it has so many other benefits, but it does make a certain sound, like how glass against glass sounds different from wood against wood. Some people solve the problem with a plastic-type material on the mandibular, which works almost like a night guard, but that is subject to wear. I do a lot of dual arches and have never had problems.
IDT: Regarding long-term durability, how are these restorations holding up in the mouth?
Adar: Some of my dentists see their patients periodically and take the restorations out to change the screws, and what has shocked me is how clean they are, especially on the intaglio surface, if they were designed correctly. It is amazing. You need a modified ridge lap, not a ridge lap like on a denture, but I have seen great long-term results with no breakage or chipping because it is monolithic. The only time breakage occurs is when the impressions—and, thus, the models—are not accurate, because zirconia does not forgive. I teach a system that is very accurate for capturing impressions.
IDT: What is the repairability of these large zirconia cases?
Adar: You cannot repair zirconia. You need to redo it. If it breaks, you cannot solder it. However, there is a reason any time it breaks: either the wrong indication of space or an inaccurate model. Those are the risk factors that all dentists should know. I put it in big, bold text for my clients. If they provide X-rays, everything is accurate, and the space is adequate, the outcome will be successful. If there is insufficient space and they still want zirconia, we cannot guarantee success.
Regarding adjustments, we are able to utilize a simple protocol with 3D printing. We duplicate the conversion with whatever changes are requested, and we use that as a reference. Alternatively, we can copy exactly what they have as a conversion, but once they try-in the printed version, they can make any modifications they desire, such as adding to the intaglio surface if they want adaptability, adjusting the bite, or moving the midline. We also can print a try-in of another design. But if the print is confirmed, and the bite and intaglio surface are perfect, we use that information to copy it. After it is copied and executed with zirconia, the typical delivery time we have now is 2 minutes, 20 seconds for dual arches with no adjustments, which is amazing. However, if additional modifications are requested—such as the patient complaining about a food trap, requiring more ceramic to be added—then we need to charge an additional fee because starting over to add ceramic underneath the intaglio is time-intensive. So, the best strategy is to do all the functional temporaries in the mouth via milling or printing; we print the try-in, adjust, the pink is waxed to see where the papillae are, and we go straight to the finish.
IDT: Do you polish or glaze?
Adar: I always polish. I have methods for polishing zirconia in the green state. I have found that it is really slick when it comes out after polishing that way. You can easily shine it up if around the gum if you want to. But I use liquid ceramics, not glaze.
IDT: Does that affect the wear on other materials or natural dentition?
Adar: No. It is low-fusing and a very thin layer. It does not impact the bite unless you make it too thick.
IDT: In the end, why is zirconia your preference for full-arch restorations?
Adar: Every case has a shelf life. Certain materials may be beautiful at the time of delivery, and they may be called same-day permanent teeth, but they are not permanent; they are temporaries. Every product has its own indication. Zirconia is not for everything.
However, zirconia can look as beautiful as layered porcelain. In fact, I performed a double-blind study to make sure that my zirconia looks as good. For seven different types of cases, I fabricated two sets of each—one with a layered glass-ceramic, and one with my system for monolithic zirconia. I put them in A and B boxes and sent them to the dentists. I asked them to try-in each one and ask the patients which ones they preferred. All seven patients selected the solid zirconia. So, my conclusion is that we do not need to layer.