Ease of Use
Ultimately, the goal is the best-looking, best-performing restoration possible. However, zirconia affords lab professionals the opportunity to easily and consistently provide restorations. That is due largely to the benefits of CAD/CAM and the digital workflow.
“Zirconia is very easy to use,” Hatzakortzian says. “Then the greatest advantage you’re going to have with zirconia is that everything is done digitally, so you don’t have any more casting or waxing or anything like that. If a patient breaks the restoration or it gets lost, it can be remade because milling centers usually keep the files for up to 10 years. So anytime between that, if something does happen, we could just go in and remill it instead of the doctor bringing the patient back in and taking an impression.”
“Zirconia is easy to work with when you control the workflow and know what you want to see as a result or product of your labors,” Godfrey adds. “Every lab has its own workflow, and 2 labs produce different results, even [when] given the same zirconia. It’s the technicians in the labs that make the result work, not the zirconia itself. It should be said that every zirconia will have a different way of absorbing stains, blocking out dark stumps, or generally allowing light penetration, based on its composition. Scientifically, the majority of zirconia out there is stabilized with yttria, but different things happen when you get one that is stabilized at 3% versus 5%, and quite another thing when stabilized with calcium or erbium. Those are not quite as common but are out there still, and they produce a different result and require a different amount of work to get to the correct value/chroma. A good technician should be able to see and compensate for these things, but many dismiss these zirconia as not being worth the effort because of the amount of time it would take to correct the workflow.”
Further, according to Kopp, precolored zirconia makes the process faster and easier.
“Restoration making is established and easy, and a very good fit can be reached due to dry milling,” she says. “With the introduction of precolored zirconia material, it is easier to get restorations with good color match.”
Using a shaded zirconia not only makes it easier to achieve the desired esthetics, but it can also help create a more durable restoration, Fernandez says. While some workflows call for applying stains to the zirconia before sintering the material, Fernandez says any moisture, including that from stains and glazes can, have negative impacts on unsintered zirconia which is why zirconia is milled dry.
“We see that a lot of zirconias out there, especially monolithics, they have to use liquid stains between milling and sintering,” she says. “We don't recommend it. There is no need for it (with pre-shaded multilayer zirconia). We know it is easily stained after sintering without having to add any moisture to the zirconia. We've seen that that is something that could bring some issues.”
Disadvantages
But, zirconia isn’t perfect. According to professionals, for as good as it is, there is still room for improvement including necessary inventory efforts and high cost.
“Zirconia requires high-temperature furnaces (~1500 °C), and attention needs to be paid to maintaining the furnace and using the correct sintering temperature,” Kopp says. “Saliva contaminations can reduce cementations’ strength if not properly cleaned after try-in. Sandblasting is recommended. It has a lower translucency level than glass ceramics, and properly cemented restorations stick very strongly to the tooth. In case of a clinical need to remove the restoration, some effort is required.”
Zirconia is very strong, but only after it is sintered. Before it spends time in the sintering oven, it is very fragile.
Godfrey sees the fragility and cost of zirconia as a bit of a drawback.
“The material is quite brittle, and the supply cost can be rather high when you are in the business of producing All-on-X (AOX) solutions,” he says. “You must keep inventory in that circumstance, because if it should so happen that your AOX chips or breaks before—or during, heaven forbid—sintering, you need backup discs to keep producing. Lab [professionals who] focus on crowns and bridges generally don’t need to throw multiple discs at a problem. [It] can remill a single unit with relative speed and ease. [This is] not so for an AOX. Crack one of those, and you’ve got to not only add the cost of a new disc but also 1 day of lab time, owing to sintering, milling, and postprocessing. AOX is rightly a costly affair.”
Keeping Costs Low (and Consistent)
Zirconia is relatively low in cost and seems to be getting less expensive every day. This is a benefit to everyone involved—labs have cheaper operating costs, dentists can make more money, and patients don’t have to spend as much.
“It’s actually cheaper now than in the beginning,” Hatzakortzian observes. “It was more expensive, but now, because it’s all done digitally, you actually have the prices going down. With a PFM, it’s very hard to find good lab technicians to bring into the laboratory. So you have a scarce resource when it comes to lab technicians. It’s actually cheaper to fabricate as a zirconia restoration than traditional PFM.”
According to Lawson, Insurance companies are paying more for zirconia restorations than PFMs.
“Reimbursement rates are typically higher for zirconia restorations than they are for metal-based restorations,” he says. “But the laboratory bill is much lower for as the zirconia crown than it is for a PFM crown in most large dental laboratories, just because there’s no metal cost associated with zirconia. I think lab [professionals] have gotten so efficient with making zirconia crowns that [it] can offer them at sometimes outrageously low prices.”
According to Sipperly, there is another benefit on the cost-saving front because zirconia is not at the whim of the metals market; it is a fixed cost.
“Metal varies daily due to the precious metal market,” he adds. “You have nonprecious metals, semiprecious metals, and precious metals. They all have different alloys and gold content. They change on price—with the exception of nonprecious metal—daily. With zirconia, you have a fixed cost. Let’s say that a 98-millimeter disc of good quality zirconia, today, sells for about $120. You get about 20 crowns, on average, out of that. So that’s $6 per unit material cost per crown. Just a couple of weeks ago, gold was $1900 an ounce.”
What’s the Best For the Lab
Zirconia’s properties can be confusing, especially because of how it’s manufactured.
“That’s less well understood,” Lawson says. “Zirconia, essentially, is fabricated from a powder that looks like chalk dust. And then they put it into a mold and compact it into something that looks it’s like an oversized hockey puck, but it has the consistency of sidewalk chalk. The way that they compact it into that hockey puck can affect its properties. If it is compacted only from one direction, called uniaxial pressing, the zirconia may not be as homogenous as if it is compacted from all directions, called isostatic pressing.
“The composition of the powder is usually relatively standardized because there are only so many companies in the world that make powder,” he continues. “And a lot of dental manufacturing companies aren’t making their own powder; they’re buying the powder. But they will typically put some of their own additives in there. For example, many manufacturers will add their unique color additives. They don’t really specify, so it’s hard to know what else they could be adding to the powders, but you wouldn’t expect them to be too compositionally different from each other.”
According to Godfrey, there isn’t just one type of zirconia. Manufacturers offer different formulations based on desired traits, strength and esthetics, and how the material is produced.
“Today, manufacturers of zirconia differ tremendously in product offerings, primarily due to production processes and powders used,” he says. “Zirconia can be hot isostatically pressed and can offer yttria stabilizers or erbium-praseodymium stabilizers for a different effect, in terms of color and translucency. These don’t all sinter the same and vary significantly from offering to offering, [but] these things must be taken into consideration when [lab professionals] choose new products. You’ve got to give it an honest effort. It’s a science, but there is art to this science with variables all over the place. You can increase sintering temps slightly for better translucencies, and you can switch to a microlayering technique to produce a depth and warmth of color.”
Per Hatzakortzian, the restoration’s location has an impact on what type of material to use.
“If you’re looking for anterior zirconia, you got to make sure that the Yttria is pretty much 4 and higher,” he says. “The reason for that is you’re going to get much more translucency, but you’re going to lose the strength. And then anything for posterior the yttria level should be around the 3s, which is pretty much giving you much more strength, but less translucency. Again, in the back, you’re not worried about the translucency or the esthetics too much. You’re actually looking more for functionality than the esthetic.”
How do the lab professionals know the best type, and how much, of zirconia to stock? With so many shades and thickness available, inventory costs can add up quickly. Sipperly advises that most labs only need a couple of different types on hand.
“Obviously, they want to use only 2 or 3 because that’s less inventory dollars,” he says. “There are about 16 VITA shades and 1 or 2 bleach shades that they might need, and they come in all different thicknesses. So, even though there’s 1 diameter, there are 3 or 4 different thicknesses that [labs] may need to carry. The goal is that we want to try to use the least the number of zirconias that we can to do our work, but in reality, they’re going to need 2 or 3, hence the anterior zirconia and the high strength zirconia, there’s even a zirconia for abutments, even higher strength, so it’s all over the board.”
While it’s a good idea to keep multiple zirconia shades on hand, Fernandez says multilayered zirconia options allow dental labs to reduce the types of zirconia they need to keep in stock. By adopting multilayered discs of zirconia, a lab can use the same type of zirconia for any area of the mouth and any types of restoration from thin veneers to full-arch, implant-retained bridges.
“So we have the simplicity of inventory right there,” she adds. “We are not having to choose different levels of translucency nor strength. So at the end it is a type of an artistry without compromise.”
Zirconia Is the Real Deal
For all the things that Superman and zirconia share in common, there is 1 important difference—Although Superman exists in comic book pages, toy aisles, and in the movies, zirconia is real and it makes lives better for lab professionals, dentists, and patients every day.
