An Esthetic Alternative for Substructures
A Q&A With Alexander Wünsche, CDT, President of Zahntechnique in Miami, Florida
Inside Dental Technology (IDT): Why has the introduction and proliferation of high-performance polymers in dentistry been significant?
Alexander Wünsche, CDT: It is just an evolution in dentistry. In recent years, we have progressed from high-noble metals to noble metals to non-precious metals, and then from acrylics to glass-ceramics to zirconia. The industry went crazy over zirconia, but we also recognized that it is not without limitations. In our pursuit of more versatility, we looked to the medical industry—especially surgical orthopedics—because they have some materials with amazing capabilities for the body. In particular, certain polymers are almost 100% biocompatible. With some, nothing sticks to them, so they do not become saturated with plaque or bacteria, which is fantastic. They are very stable, and they can be fabricated via multiple methods including pressing and milling.
IDT: Sometimes, something sounds good in theory, but clinical evidence does not back it up. What is the clinical evidence thus far with high-performance polymers?
Wünsche: The long-term results I am seeing are fantastic—even better than I thought they would be. You never know how any new material will perform long-term in the oral environment. Working with high-performance polymers, I have been amazed. We have been milling these materials for more than 8 years, and we have had fewer issues than with any other modern material. We are not performing intensive testing like a university would, but we have live cases and experiences, and we have the lowest numbers of remakes and issues with these materials.
IDT: What are the most useful indications?
Wünsche: We have tried using high-performance polymers for a number of indications, ranging from removable over semi-fixed or semi-removable with implants to removable partials. Currently, we utilize them primarily for larger implant reconstructions—at least two implants, and usually full arches. These materials are so useful for complex implant cases because they are biocompatible and the color is great for esthetics. They do not produce the gray shine that even opaqued metal does. They do not have the bright white shine of zirconia or that high-value color. They are more like a grayish-beige color, very similar to bone. What is underneath gingiva naturally? Bone. So, for full-arch cases, these materials produce great coloration; for example, for a hybrid restoration, we just cover the bony color with pink tissue. If you know how to utilize a pink composite, you can fabricate a highly esthetic restoration without any artificial grayness or high value underneath. Esthetically, I love it.
The material also is very lightweight, which may be an advantage, though we do not necessarily hear complaints from patients about other prosthetics being too heavy. It does have a very comfortable wear, to which patients respond extremely well. When we restore a patient who previously had a full-arch zirconia hybrid in the mouth and complained that it was too loud or felt too hard, they are telling us that the high-performance polymer feels much more comfortable.
We do not use high-performance polymers for monolithic prostheses, which can be both advantageous and not. Having the fewest different materials combined in the mouth is simpler. However, for maintainability in the future, having both a polymer framework material and a veneering material along with a pink composite is great. If there is tissue recession, we can just add a bit more pink composite to what is already layered; this can be done by the dentist chairside or in the laboratory, and it is quick and easy. Conversely, a zirconia restoration needs to go back in the oven, which presents the risk of fracture because zirconia gets stressed when repeatedly heated. The other advantage to a polymer framework is that if there is a failure in the veneering material—for example, on a crown or a bridge segment on the framework—we can just take it off, remill it, glaze it, and put it back on. We had a mandibular hybrid with a high-performance polymer framework and lithium disilicate crowns, and one of the incisors broke off, along with a piece of the polymer; we just removed the two adjacent teeth and basically milled a zirconia bridge, bonded it to the framework material, finished the pink composite, and it was unnoticeable. That is just one example of a restoration that was retreatable—almost repairable. That cannot be done with zirconia. When zirconia breaks, we basically need to start from scratch with a very expensive repair.
IDT: How about contraindications?
Wünsche: Like every material, there are pros and cons. One contraindication for high-performance polymers is long cantilevers; even if the anterior-posterior (AP) spread on the full arch would allow, for example, a two-tooth cantilever, I would not do it because of the stress on the material. High-performance polymers are not as solid as zirconia or even some composites. They exhibit a certain flexibility, especially on long cantilevers; over time, the tendency would be either for them to break or for the veneering material to flake off.
Another contraindication is when the vertical space is insufficient, forcing the framework to be very thin. Those same risks related to the flexibility would be present. Obviously, you would not use high-performance polymers for a full monolithic restoration because they are not pretty. They are pretty substructure materials as a replacement for bone, but they need to be veneered.
IDT: Are there any other special considerations when deciding which cases to use these materials for?
Wünsche: I evaluate a whole array of risk factors for every case we do, especially large implant cases, and one is the age of the patient. For a younger patient who needs a long-lasting and comfortable restoration that is not too forceful on other aspects of the bone, dentition, muscular system, etc, a high-performance polymer is preferable. Conversely, for an older patient who needs something very esthetic and straightforward, we would be more inclined to use zirconia.
Additionally, a high-performance polymer restoration is a high-end product. It is definitely labor-intensive. It is technique-sensitive. It is one of our highest-priced products, not only because of the time it takes to fabricate but also because of the knowledge that had to be accumulated in order to utilize these materials well.
Another factor is the lightweight nature. For a maxillary telescope restoration, a high-performance polymer framework is fantastic because that is a restoration that needs to be lightweight.
IDT: Are dentists mostly accepting of these materials? How do you educate them on exactly what this class of materials is?
Wünsche: It is very mixed. We have many dentists who are very open and love it. We have a small number of dentists who specifically ask for it because they are very educated themselves. And, of course, we have some who say it is too progressive; these dentists had a hard time accepting zirconia for many years, but they have now, so maybe they will embrace polymers in 5 years. We do promote a consultative approach, however, so many of our dentists trust us when we recommend certain materials and explain the benefits.
We do also need to take into account the dentist's ability to work with these materials. For some, a simpler restoration is more likely to be successful.
IDT: When you are working with these materials, what is important to keep in mind in terms of processing in the laboratory?
Wünsche: These materials usually have a very high density. Nothing really sticks to them, so we needed to develop workflows whereby we could bond composites, bond ceramics, and then also bond composites to ceramics, so we have that onion layer of material in some areas. We had to be really diligent in determining how to accomplish all of this and which materials work best. Over the years, we developed a very strict protocol for bonding composite to polymers, how to bond ceramic—even if it is lithium disilicate or zirconia—to polymer, and how to actually create a seal between the composite and the ceramic to avoid any discolorations.
The other crucial factor is knowing what the minimum thickness of a polymer framework should be. What is the minimum area for a connector, given the flexibility? What is the minimum size of a preparation for the crown or bridge to be stable? We experienced some fractures as we went through the learning curve, and every laboratory needs to go through their own.
IDT: What do you need clinically from the dentist?
Wünsche: Accuracy is the key. For example, for a hybrid—the most common application for these materials—I need to make sure I am getting a really accurate record from the dentist because we want to keep the contact of the gingiva in the non-esthetic areas in polymer, rather than veneering material, because it is healthier for the gums. There is less porosity and less bacteria settlement. I need to know that the dentist knows what they are doing in terms of not only impressions or scans but also bite, occlusal records, functional records, etc. I do not want a lot of occlusal adjustments to be necessary.
IDT: What is the repairability factor for high-performance polymers?
Wünsche: As I mentioned previously, if a restoration includes multiple materials and one fails, it is repairable. However, it is very important to understand that all of these polymers are like the other progressive materials we have on the market: They are not repairable themselves. If I have a framework fracture, it is done. I need to rebuild the framework. We can repair veneering material on top of the framework, but the material itself is not repairable.
IDT: What developments would you like to see in the future?
Wünsche: My wish list is long, but at the top, I would definitely love to see a realistically printable high-performance polymer. I know some people are already printing them, but the methods they are using are still too complex to really utilize in the everyday laboratory workflow with our equipment. But that would be very helpful.