What do Superman and zirconia have in common? If you said strength (both are unquestionably strong), esthetics (they both look great—even disguised as Clark Kent, Superman is still a dreamboat), and affordability (sure, this one is a little bit of a stretch, but Superman provided his services free of charge), then you are right.
Of course, claiming either as “the best” in their respective fields is somewhat subjective, but it’s getting harder and harder to argue that opinion, especially where zirconia is concerned (Batman fans would likely disagree as to whether Superman is the best superhero).
There’s a lot to know about zirconia, and dental lab professionals need to understand how this material helps them, doctors, and patients.
History
Zirconia is a fairly new material used in dentistry (only in the last 20 years or so) and is usable only in the CAD/CAM workflow, supplanting porcelain-fused-to-metal (PFM) restorations.
“In the early 1990s, the Nobel Company started producing the world's first sinterable dental ceramic produced by CAD/CAM, a material called alumina,” says Ben Godfrey, application engineer at Axsys Dental Solutions. “But, due to difficulty of use and lack of longevity, this material sprung up and then died just as quickly, and the market needed a new material. On the heels of those new cylindrical dental implants, [Per-Ingvar] Brånemarklicensed and partnered with Nobel to produce Procera brand zirconia. The entry price tag was quite high, as the new digital process required investment in a probe-based scanner that touched the die as the die spun—leading to many margin breaks as the probe rode along any undercut and tended to easily break thin edges on stone dies.
“The system was intended to scan only stone dies and produced only thimble copings until software updates in the early 2000s,” he continues. “It wasn’t until the mid-2000s that the full-contour zirconia market got its legs, owing to failed porcelain-to-zirc in years previous. Around about ’08 to ’09, when proper liner agent was developed for layered zirc, the market for monolithic zirconia claimed a lot of ground from PFM and gold.”
Nathaniel Lawson, DMD, director of the Division of Biomaterials at the University of Alabama at Birmingham School of Dentistry, remembers when zirconia made it big. “When it first started, it was just the framework as zirconia,” he says. “So, it was something that they were using just for its strength. And then they had to put porcelain over it to impart enough translucency to make it look natural in the mouth. But when the zirconia revolution started was when they started making zirconia that could be monolithic, so it didn’t have to have any veneering porcelain over it.”
Claudia Fernandez, a lab technician for several decades, and currently a territory sales manager at Smart Dentistry Solutions has been working with zirconia for many years and recalls the early struggles with debonding issues, and the lack of esthetics relegating the material to posterior use. But with better complementary materials and workflows, those challenges are issues of the past, and today zirconia is well suited to play a role in almost any type of restoration.
“Now it has evolved to being more aesthetic and more translucent,” she says. That's thanks to all the technology that now used in manufacturing zirconia.”
Comparison
Zirconia gained traction in dental restorations because of its strength, wear-resistance, and biocompatibility. When compared with older analog materials, like PFMs, or even newer materials, like Ivoclar Vivadent’s IPS e.max, zirconia has clear advantages.
Lawson looks to a study conducted by the Journal of the American Dental Association revealing 277 American Dental Association Clinical Evaluators’ attitudes and opinions towards zirconia.
“The biggest thing was that 57% of people said that zirconia’s biggest advantage was its strength,” Lawson says. “And then 14% of people said its [advantage is] versatility. What we meant by that was, ‘Can [zirconia] be used for a whole bunch?’ It can be used as a crown; you could use it for a hybrid prosthesis, meaning you could replace an entire arch with it; you can use it for an implant abutment; you can use it for a lot of different applications.
“The third was wear resistance because it doesn’t really wear away over time,” he continues. “And then the fourth was cost—and I’m surprised that wasn’t higher—because zirconia really has reduced laboratory costs for crowns, just because you can manufacture them relatively inexpensively.”
According to David Sipperly, sales training manager at Dentsply Sirona, a lack of metal components means that esthetics are improved, and biocompatibility is better.
“All-ceramic restorations typically have better esthetics than PFMs, because you’ve got a metal substructure and gray metal substructure base, particularly when you have tissue recession, you can see that gray line or a metal halo in a patient’s mouth,” he says. “Or you can see a gingiva tattoo that some people would have because of the metal. And some people have sensitivity to metal, so all-ceramic or metal-free is the way to go from a biocompatibility and esthetics perspective. Now that being said, PFMs were the norm 15 years ago. It was 80% of the business, [with] 20% all-ceramic. Today, it’s completely reversed. All-ceramic restorations are 70% to 80% of the and PFMs are 20% to 30%.”
Zirconia’s composition makes it not only esthetic but also strong.
“One of the benefits zirconia versus PFM is you have no metal showing,” says Raffi Hatzakortzian, co-owner of Alien Milling Technologies. “If the patient’s gums do reduce over time, you don’t have to worry about that metal showing. The second advantage would be that it’s actually stronger than PFM, so you do have less chance of breaking.”
But it isn’t just the patient who benefits from a zirconia restoration. Dental lab professionals realize the advantages of using the material.
“The first big one is labor-saving,” Godfrey says. “With the advent of zirconia produced via CNC, you now need only click the mouse to do your design digitally, and as the project is on the screen, you can click buttons and boxes to make things appear, disappear, or adapt. For example, with a click, you can adapt your crown to the contacts perfectly. Secondly, in terms of material selection, zirconia today has dozens of varieties allowing for unprecedented flexibility in adapting to shades. There are hundreds of brands of zirconia on the market, and each can come in several varieties of strength and translucency characteristics. We’ve come a million miles from dead white copings 30 years ago. It can be a daunting task finding a zirconia that works best for your case, but as many people are finding out, once you know what you need from your workflow, it’s a pretty simple process.”
Esthetics
According to Elke Kopp, new procedure marketer at 3M, form and function are the most critical qualities of dental restorations. On the form front, zirconia has an edge.
“The big advantages of zirconia are that they are highly biocompatible,” she says. “They are metal-free; they have a toothlike color; they have a lower minimal wall thickness than e.max, and minimally invasive restorations are possible. They can be dry milled, which is an effective manufacturing process; they have a flexible use depending on needs and are easy to cement. There is no discoloration in the mouth; and low wear. Although veneered zirconia is the golden standard in esthetics, monolithic zirconia is reaching high levels of esthetics.”
A lot of this is, of course, subjective, and it seems to vary depending on who you talk to and their role.
“This is a topic that always stirs debate,” Godfrey observes. “Esthetics are one way in the eyes of the lab [professional], another in the eyes of the dentist, and another in the eyes of the patient. If you want to have an objective discussion, you have to resort to talking about zirconia in an ‘on-paper’ sense. Zirconia can be produced as white or preshaded, and it’s often that lab professionals go for preshaded zirconia because it accelerates the workflow and eliminates the white spots that you’d see as a clinician making small adjustments to the crown at time of seating. “Therefore, if you grind into a preshaded A3 crown, you will never see white spots—the color goes through the whole material,” he continues. “There are a great many methods of achieving finer detail of stain, from pre-sinter liquid application, to glaze kits that transform the look of any zirconia according to the skill of the artist. The ceramists don’t need to fear losing their jobs to automation…yet. Many technicians today don’t put the same effort into zirconia as e.max by virtue of the fact that the 2 materials start from a different esthetic point—e.max has qualities in it that make it easier to achieve the perfect shade without much effort, and almost all technicians prefer to put porcelain on a crown to achieve a quality shade.”
A more recent advance in the esthetics possible with zirconia restorations is the development of multilayered zirconia discs that combine the strength of zirconia traditionally used in the posterior region with the enhanced translucency of zirconia designed for use in the anterior. Fernandez says these materials allow labs to use zirconia without compromising strength for translucency or vise versa, and the manufacturers of these materials are getting better and better at creating smooth transitions between the layers.
“It means that it goes from a veneer as thin as a veneer can be to inlays, onlays, and all the way to a 14-unit, implant supported structure or custom implant abutment structure,” she says.
