The Esthetic Option Anyone Can Bond
Inside Dental Technology delivers updates on digital workflows, materials, lab techniques, and innovation in dental technology through expert articles and videos.
March 1, 2023
Volume 14, Issue 3, March 2023
Page(s): p. 10
Inside Dental Technology (IDT): What are the ideal circumstances for glass-ceramic restorations?
Joshua Polansky, MDC: I use lithium disilicate for the majority of our veneer cases. The advent of millable options has been significant; the ability to mill these materials makes them our go-to option for highly esthetic digital cases. Beyond veneers, we sometimes use lithium disilicate for crowns when dentists request it, though we prefer zirconia for its strength. Additionally, we occasionally use lithium disilicate for jacket crowns when we want high esthetics, such as on the centrals. We do not use lithium disilicate for bridges, and we do not splint it, even though many people say that is possible. A manufacturer's indications are helpful, but a laboratory should develop its own indications as well; when a restoration breaks, the dentist does not want to hear about the manufacturer's indications. Zirconia just holds up better for anything with a substructure. I have had cases when a pontic breaks off a lithium disilicate Maryland bridge, which is a problem. With metal or zirconia, the whole restoration breaks off, which is not as bad because it can just be re-cemented. When the pontic breaks, the restoration needs to be remade. For that reason, I really stay away from splinting with lithium disilicate when occlusal forces are involved.
IDT: Is there still a place for feldspathic ceramic in modern dentistry?
Polansky: I love feldspathic ceramic. It can be technique-sensitive, but many technicians in our laboratory have been trained with it, and in our opinion, it still looks the best. There is definitely a place for it; a large portion of our new clients seek us out specifically for feldspathic ceramic because, apparently, not many laboratories are offering this restoration. We love it.
IDT: Are there other situations you encounter frequently when a dentist might ask for a glass-ceramic such as lithium disilicate and you need to push back?
Polansky: Yes. There is a misconception that lithium disilicate can be used on anything, and at any thickness. Dentists sometimes ask for no-prep veneers, but we need a minimum of 0.2 mm to 0.3 mm. When I was hand-processing feldspathic ceramic, I could make it 0.0 mm. With pressable materials, however, we need a certain thickness in order to deliver the strength the dentist expects.
IDT: Conversely, are there times when a dentist defaults to zirconia and you recommend a glass-ceramic?
Polansky: Yes. We have dentists who have asked us for zirconia veneers, and we tell them we do not do those. Lithium disilicate can be bonded very well, which is super important for us. Any time the dentist wants strength via bonding, we prefer monolithic lithium disilicate. I have dentists who believe in zirconia bonding, and I am aware of the literature supporting it, but the clinical results I have seen have not been good. I am running a business, so I cannot recommend something I do not believe in. If the dentist still wants zirconia, I will do it, but I recommend against it.
IDT: When do you micro-layer lithium disilicate, and how do you treat it?
Polansky: We micro-layer the majority of our lithium disilicate cases, as our dentists have become accustomed to our layering skills. We can make the units look good with just stain, but our experience has been that micro-layering just makes them pop more.
IDT: You mentioned milling vs pressing lithium disilicate. Is the material the same in all forms?
Polansky: There are differences, but not in the material itself. I can recognize a restoration fabricated by hand on a good analog model because we can thin it out more in the processing stage, whereas with milled restorations, we need to trust the machine. Accurate margins also are important when milling because I cannot compensate like I can with an analog model.
I do use both methods, depending on how the case arrives at the laboratory. If I receive a physical impression, I press the restorations. If it is a digital case, I mill them. Moving from analog to digital, or vice versa, creates the possibility of introducing processing errors.
IDT: What are the long-term clinical results you have seen with lithium disilicate?
Polansky: Lithium disilicate has proven to be durable in the mouth over time. Esthetically, in my opinion, it blends better in the mouth for single units than zirconia. Zirconia tends to lean toward a higher value, whereas lithium disilicate leans toward a lower value. We adjust accordingly.
IDT: With multiple lithium disilicates on the market now, along with lithium silicates and other glass-ceramics, what are the important differences to note?
Polansky: The density is the primary difference in lithium disilicates. Think about if you have one glass filled with sand and one filled with rocks, and you pour water into each. In denser materials the glass matrix is tighter and cannot be penetrated during investing, so there is no reaction layer. So, not all lithium disilicates are the same, which also means they cannot all be processed the same. Following the manufacturer's instructions, especially pertaining to firing temperatures, is extremely important.
The lithium silicates that we have available are primarily reinforced with other material, such as zirconia. There are also other glass-ceramics that demonstrate excellent esthetics, but their strength is not ideal. For cases when esthetics are the highest priority, however, they are good options.
IDT: How impactful would printable glass ceramics be if they become reliable and economically viable?
Polansky: It would be huge. I have seen enough to know anything is possible, so I believe printing technology probably will overtake milling in the future. I know some people are already printing lithium disilicate, but currently, the materials are not esthetic enough. It is similar to when zirconia first came on the market; the materials are strong, but they do not look great. I am sure they will improve, however, and printing technology is more user-friendly than milling, so it will be very impactful.
