New Zirconia, Oven Combination Set a Sinter Speed Record

Dental Lab Products, Dental Lab Products October 2022, Volume 44, Issue 5

For the first time, full-arch zirconia can be sintered in less than 4 hours, a significant improvement over the typical 16-hour cycles.

Three years ago, Zubler USA began working with a lab and milling center to develop a full-arch workflow for zirconia. Zubler USA provided the milling machines, sintering ovens, and zirconia, leading to fantastic results. But one area needed improvement: the zirconia sintering time.

Full-arch zirconia typically takes more than 12 hours to sinter; in this case, it was a 16-hour cycle. Zubler USA owner and President Bryan Parker decided that needed to change, so the team went to work on creating a zirconia with a faster sintering time. The result? After several years of research and testing, the company released 3:45 zirconia. Unlike any other zirconia on the market, according to Zubler USA, it can be sintered in 3 hours and 45 minutes, a significant improvement.

“Before, when you loaded the oven, you couldn’t touch the work for 16 hours, creating a bottleneck,” Parker says, noting that, with this material, new cases can go in the ovens every 4.5 hours. “We reduced the time but are still able to get the same results as with a 16-hour cycle, and for a lab that’s huge.”

Now, labs can turn their ovens over more than once a day. For example, if a lab starts the process at 8 AM, they can begin to sinter at 12:30 PM and again at 5 PM—meaning 1 oven can now do more work in 1 day, Parker says. Labs can take on rush cases they would have had to turn down before, bringing in more revenue.

Many technicians thought achieving such a comparatively short sintering time was impossible, but in the few months since the material was released, more than 700 arches have been placed, according to Zubler USA. Parker expects that number to climb rapidly.

So far, technicians have been surprised by and happy with the results, Zubler USA Vice PresidentChris Wilson says. Although many customers would call the company asking for help in speeding up their sintering cycles, none expected to get it to under 4 hours. It became clear that lab technicians were looking to increase their throughput, which was another reason for Zubler USA to work on quicker sintering times.

“The answer was always the same: the zirconia manufacturer dictates the cycle for the zirconia, not the oven. The oven provides the capability,” Wilson says. “We have ovens that go so much faster than the parameters zirconia manufacturers provide, so we wanted to take advantage of those capabilities.”

Developing the Zirconia

During the development process, Parker ran much of the testing, with the goal of creating a material that could withstand the temperature increases and necessary heat rates for faster sintering while maintaining optimal esthetics.

The team continually repeated experiments, because it was important for Parker to achieve an always consistent result; 96 or 97 out of 100 wasn’t enough. The outcome is the same every time, with the high-quality raw materials and manufacturing processes being a big part of the reason the sintering time was reduced significantly. “We wanted it to be fast,” Wilson says, “but we didn’t realize how fast it would be.”

A Focus on Strength and Esthetics

For these types of restorations, large chunks of zirconia are typically used to support the mechanical structure against the forces of heating and cooling, because they can cause warping and cracking during sintering. Zubler USA’s zirconia sintered with the 16-hour cycle never required that support, and it was important for that to remain the case with the new, faster-sintering material, Parker says.

Even with the rapid heating and cooling 3:45 zirconia requires, the stable material does not need extra support, Wilson says, saving zirconia that can be used for single posterior units or 3-unit bridges.

“The worst part about milling with support is after you sinter the zirconia, you have to cut the support out,” Parker says. “By doing so, you risk cracking, so it was very important for us to continue to mill without a support and to have the stability and the fit after it was sintered, so it can go from the sintering oven directly to layered porcelain or stain and glaze.”

In the past, you could speed up sintering times for single units (never a full arch like what is possible with 3:45), but the result was not the beautiful restoration doctors and patients seek. That is not an issue with 3:45 zirconia.

“We ran a lot of experiments in our different sintering ovens, and I’d always cringe as I watched it come down because I thought for sure esthetics were going to be an issue, but they never were,” Wilson says. “It’s amazing to see what it looks like after it’s been sintered. It’s just a great material to work with.”

Achieving the right chroma and translucency was paramount, and probably the biggest challenge, Wilson says. “It had to present well, be reliable and consistent, and perform well,” Wilson says. “The performance we got pretty quickly and the repeatability we got very quickly; it was more getting the color right, which we did.”

The Ovens

Investing in the right oven is just as important as the material, because most were not built to handle sintering so quickly. Many do not have the space to complete many cases at once. Zubler and Mihm-Vogt ovens handle the sintering, with some holding 6 to 8 full-arch cases and others as many as 10 to 12.

“The only thing we are challenged by is the limitation of some of the ovens,” Wilson says. “Some can’t sinter that fast. The tables won’t come down that quickly, or [even though] the ovens can reach the temperature ranges and heat rate necessary, they won’t allow you to cool down fast enough.”

The zirconia was repeatedly tested in Zubler and Mihm-Vogt ovens, so there was no doubt they could handle the material. “It’s the zirconia and it’s the oven,” Parker says. “And it’s very critical to put porcelain or some type of porcelain material on the zirconia after it’s sintered.”

The Zubler USA porcelain oven plays an important role, Parker says, because it provides the even heat distribution and cooldown that allow for a better success rate. “The last thing you want to do is spend the time, money, and effort on an arch like this and get to the end of the process and it cracks, because at that point you have no choice but to start over,” he says. “The equipment helps you achieve the success you want, and Zubler has been shown to have next to zero remakes with its ovens.”

Zubler USA is known for offering top-quality ovens that last, but a little help keeping them in good shape never hurts. The faster sintering time for the 3:45 zirconia is better for the ovens, Wilson says, because they spend less time at oxidizing temperatures.

As ovens improve, faster sintering times are the next logical step, Wilson says. “Everything is going in that direction,” he says. “We wanted to be ahead of the curve.”

What’s Next

The company is already working on its next release, which should be out shortly, Wilson says. The single-unit, multiple-layer material, with a sintering time of 20 to 30 minutes, is more complex than the 3:45 and is another significant advancement for zirconia restorations. For the past 2 years, the team has been tweaking the color, chroma, and translucency to get it just right.

Zubler continues to innovate, and today offers a zirconia material that sinters in a time frame no one thought possible. The team strives to offer “unbeatable” products, according to their mission statement.

“We built the company based on awesome products and awesome customer support,” Parker says. “We don’t want to offer a product unless we know it’s been tried, tested, further tested, and perfected, because our reputation is more important than a fly-by-night product. That’s why we offer the products we do and support our customers in every possible way.”