The Evolution of Dental Materials

How new innovations in millables and other materials are making the future brighter than ever.

The birth of CAD/CAM changed everything for labs. Suddenly, it was possible to do tasks in minutes that used to take hours of painstaking labor. In the beginning, the results might have left something to be desired, but the promise was there. Fast-forward a couple of decades, and now many dental technicians use at least a portion of a CAD/CAM workflow almost daily.

But none of this would have been possible if millable materials hadn’t evolved along with the equipment technology. Since the advent of CAD/CAM, the results have only been as good as the materials that are used. And those materials? They’ve taken a huge leap forward. Here are some of the biggest innovations in digital materials and what the future of the industry might look like.

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Evolution

Like any technology, early mills were expensive and found in few labs. But over time, with both improvements in performance and reductions in cost, mills are now more prevalent than ever.

“Historically, full laboratory CAD/CAM systems were either too expensive for the average laboratory or not geared toward the level of production required for day-to-day business. This meant many laboratories could not effectively integrate full-fledged CAD/CAM systems into their respective businesses,” says Dr. George Tysowsky, vice president of technology at Ivoclar Vivadent. “Today, equipment prices have lowered, average equipment sizes have shrunk and there are small steps laboratories can take, such as outsourcing, to grow or transition their businesses in a digital world. The path to in-house milling is now clearer and more achievable than ever before.”

Different labs have different needs. And, in the case of large milling centers like Custom Milling Center in Arvada, Colo., mills made specifically for dental applications are not even used.

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“We used to use machinery that was set up specifically for the dental industry,” says Ryan Faufau, Custom Milling Center’s director of CAD/CAM resources. “Today, we actually use a Haas Milling Unit. It’s a milling machine that’s set up for more of an industrial-type application. So far as our milling technology, we’re kind of a different breed when it comes to that application, which is a good thing because it gives us the ability to do some advanced milling, tool pass and things of that nature.”

Labs that adopt milling technology should consider the implications for their business when utilizing the equipment.

“Milling in-house is an aspirational goal of many laboratory owners today,” Dr. Tysowsky says. “We urge the market to not only consider the best equipment investments to make for their laboratory but also who their best business partner is for supporting not only the equipment but also their people. Adequate training, a clear backup plan when a mill needs service and exceptional customer support are all absolutely critical when integrating milling technology.”

Improvements

Not only is milling more affordable than ever, but labs can do much more than they could when they were first introduced.

“Milling technology has improved in a number of ways, including accuracy, level of software integration and automation at a scale that is accessible by the average laboratory,” Dr. Tysowsky says. “If we use the Wieland Zenotec select hybrid as an example, the average laboratory can purchase a milling machine that utilizes milling tools as small as 0.3 mm in diameter for exceptional detail; can hold eight discs, or 48 blocks, for extensive automation;  has preprogrammed milling strategies for all Wieland materials; and has a growing array of customized milling tools optimized for different material types. Although zirconia is a popular topic in regards to milling, machine automation also allows continuous and overnight milling of IPS e.max CAD. As expected in today’s world, we push free software updates to the milling machines to introduce new options free of charge to customers.”

Automation is a feature greatly increasing lab productivity. That ability is one of the most innovative features of today’s mills.

“For people who are doing more and more milling, you can leave the machine overnight and mill a few different products,” says Mark Ferguson, assistant manager at Core3dcentres in Las Vegas. “With all the different materials coming out, with the different zirconias and the multilayers and PMMAs and things like that, you can let the machine go. You don’t need somebody there babysitting it to keep reloading different materials.”

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Ivoclar Vivadent streamlines the process even further, allowing the materials to self-identify with the milling machine.

“All of our millable discs  utilize RFID technology to enhance laboratory workflow and enable automated milling of up to eight discs while minimizing the need for manual inputs,” Dr. Tysowsky says.

New zirconias take center stage

Material advances go hand-in-hand with hardware developments. Zirconia was a huge advancement for restorations, and the material continues to evolve and improve, making formerly demanding restorations possible.

“The newest product that is out in the industry is going to be the super high translucent zirconia,” says Alex Thomas, general manager of DAL DT Technologies in Davenport, Iowa. “A lot of other companies have them. We have our own version of it. It’s called the cubeX2 zirconia. It’s a lower strength, higher translucent zirconia with which we can provide a full-contoured anterior restoration. In the past, with zirconia, you’ve only been able to do a full-contoured posterior and then you did a porcelain over zirconia in the anterior. [The new material] allows us to use the zirconia product in the anterior as a full-contour. It decreases our costs manufacturing-wise for products we would use in the anterior. It’s less for us to manufacture. It’s easier for the doctor. It’s a more conservative prep for them.”

The new generation of zirconia promises improved applications and better esthetics.

“The new, more translucent zirconias are becoming very popular, very quickly, and so that’s kind of exciting to get,” Ferguson says. “The knock against zirconia has always been the esthetics when you want to go full-contour. Now we’re getting to the point where the esthetics are reaching the level of the ceramics or the pressables.”

New long-term PMMA products

Many companies have also developed multilayered, millable PMMA discs for long-term provisionals. German company anaxadent is one of them. However, Tay Harvey, director of U.S. operations at its North American headquarters in Ardmore, Okla., saw a different need for the United States market.

“For crown and bridge, it was great, but what we try to focus on here in the U.S. is the full-arch, hybrid denture restorations,” Harvey says. “I wasn’t satisfied with the layered pucks as a solution because when I talk to our customers, they said, ‘Hey, they’re beautiful, as long as your incisal edge is pretty flat, you don’t have a lot of variation in crown length and you don’t have to nest the case in the puck at an angle because once you angle it, your translucency is off.’ The colors are off because you’re picking up different layers that you don’t want to pick up. You’ve either got too much translucency or not enough. The layered is a great concept, and for the right restorations it can work beautifully. In some hybrids it works beautifully, but we got enough feedback from our customers to know that there had to be a better way.”

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Anaxdent’s solution was creating a millable disk based on its popular New Outline powders.

“In 95 percent of the cases, with New Outline, we know they’re mixing the dentin and incisal powders together in a homogeneous mix before they add the liquid,” Harvey says. “They shoot in one layer, but it brightens it up, leaving the enamel layer. It gives it more translucency so your incisal edge looks more translucent where it gets thinner.

“So I talked to Germany, and I said, ‘Hey, in this market, that’s what people are doing with the powder/liquid. I think they would be happy with that solution in a millable disk, as well, so they created about a 70/30 homogenous mix of dentin and enamel. But it’s one layer so no matter where you nest the case, whether it’s at an angle or the incisal edge is all over the place, you’re going to get a nice, translucent incisal edge.”

New temporary options

Creating temporaries with CAD/CAM streamlines the process over traditional methods, making it easier and faster for the technician to create the restorations.

“In the past, we did diagnostic wax-ups by manually waxing up a case,” Ferguson says. “Now, we can do them digitally a couple different ways: We can prep the teeth on the model and then scan it and treat it like a crown and bridge case, mill some temporaries and send those off to the doctor as shell temps. Or we can glue them to the model and give a diagnostic wax-up model similar to what we were doing when we were manually waxing up the case and then giving matrices for the doctor to do temps in the mouth.”

Technique: Creating better provisionals

Milling also lends its beneficial attributes to the production of temporaries, allowing streamlined production and consistency.

“Milling allows the use of industrially produced, fully polymerized discs such as Telio CAD for Zenotec,” Dr. Tysowsky says. “This eliminates the variables of traditional temporaries, such as polymerization shrinkage and proper mixing of components, and allows for optimized physical properties. Further, CAD/CAM technology has brought an improved level of reproducibility and efficiency when transitioning from the temporary restoration to the permanent prosthesis.

“For example, long-span fixed-hybrid zirconia cases continue to grow in popularity. The CAD file used to mill the temporary prosthesis is saved while the patient evaluates esthetics and function after a period of intraoral use. Any modifications requested by the patient and/or dentist are quickly made to the design, and the milling of the final prosthesis can begin immediately.”

The ability to make temporaries via CAD/CAM is also a very cost-effective solution.

“All the machines we sell and use can mill PMMA material,” Thomas says. “We can mill any temporary restoration. It’s quite common on those full-arch zirconia, screw-retained bridges because it is such a costly restoration for the dentist so typically beforehand they do a try-in, and that’s made out of temporary material. We do those with frequency, as well. So temporaries have come a long way in the laboratory.”

Millable Metals

It isn’t just zirconia and polymers that can be shaped via milling. Metals can also be crafted into whatever form the lab needs.

“We mill titanium and chrome-cobalt,” Ferguson says. “With titanium being classified as a noble alloy, some other labs are looking into the different porcelains for build-up on titanium, and some of those are getting really nice. Obviously, titanium’s not the easiest material to do porcelain build-ups on so a lot of labs are still skeptical about doing that, but we’re also doing chrome-cobalt milling. At that point, it’s just non-precious PFM work. We can do that for implant cases. So you can do a PFM, screw-retained bridge or regular crown and bridge cases.”

Metal milling has led to advances and improvements in lab work.

“Laboratories are able to mill their own titanium restorations,” Thomas says. “For instance, abutments and titanium bars. They are able to mill their own chrome-cobalt restorations, PFM non-precious copings and, the most talked about restoration on the market, the full-arch zirconia hybrid, screw-retained bridges. That was something that was not a restoration being done in the industry. It most likely could have been milled, but what you see is the most popular. It’s what everybody wants to do. They want to get to the level of doing their own full-arch, screw-retained, zirconia bridges.”

Metal may or may not be on the way out, depending on industry trends.

“We actually saw a wave of chrome-cobalt prescriptions on cases we received,” Faufau adds. “We saw lots of screw-retained chrome-cobalt cases just because of the compatibility of the alloy with porcelain. Since then, we’ve seen a huge shift over to screw-retained hybrid cases where it’s full-contour zirconia with some pink porcelain at the gingival. So we’ve actually seen the shift from chrome-cobalt over to the zirconia application.”

Milling is one way to shape metal, but a new advancement utilizes lasers to form a restoration’s metal components.

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“And then there’s another way to get them done,” Thomas says. “You can do some precious alloy as opposed to non-precious. It’s called the Selective Laser Melting (SLM) technology. Those are really done at some of the bigger labs. The BEGOs and the Argens are doing those. We have not purchased the equipment to be able to do it, but laser melting-as opposed to milling-allows you to do some precious alloys as well.”

Polymers

Another class of millable materials is polymers. Anaxdent, in partnership with Swiss company Cendres + Meteaux, market a new product called Pekkton. Pekkton is a polymer that is strong enough that it can replace metal.

“If somebody were considering a titanium or chrome-cobalt frame, they could use our polymer instead,” Harvey says. “There could be a lot of advantages for that plus it mills like PMMA so you don’t have to have a wet mill like you would typically have to have for a millable metal. We don’t get into the millable metals because we are focusing on finding a better way.”

Pekkton is not a full-contour material. Rather, it is best used at a replacement for metals in applications like copings.

“You could definitely use it to mill copings in cases where metal wasn’t ideal,” Harvey says. “Maybe the patient wants a metal-free restoration. It’s a good alternative there, too. It just has clinical and functional benefits in comparison to metal when you give it to the frame.”

New materials like Pekkton are designed to be an ideal replacement material because of their shock-absorbing properties.

“When you bite down, it’s not a rigid experience,” Harvey explains. “It’s an elastic feel because you have periodontal ligaments surrounding your roots, and they’re providing shock absorption. That goes out the window once implants are placed, and Pekkton puts it back. Right now there’s a lot of concern with the full-arch hybrid, screw-retained dentures being such a popular option for patients. There’s a lot of concern because we’re putting rigid materials onto the implants. The implants are rigidly osseointegrated with the bone, and now something’s got to give. It’s either going to be the implant, the joint or the bone because, in nature, that shock absorption is there. Those shock-absorbing ligaments are there for a reason. When you’re using Pekkton, you’re basically stimulating that same shock-absorbing property, which we’re really excited about.”

The effects of more detailed milling

Different mills offer different levels of functionality-some more hearty than others. For example, three-axis mills operate along the X, Y and Z axes. Five-axis machines offer the ability to operate on two additional rotary axes, A and B.

The use of a five-axis machine is dependent on the case and the customer needs.

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“Generally, if we’re notified from the customer, or if we see a case that requires the five-axis milling, we’ll apply it at that time,” Faufau adds. “ With most of the full-contour single units you mill, it’s not necessary to mill in five-axis. Most of those cases can be milled in your conventional three-plus-one. But, for example, we have to mill screw-retained, full-contour hybrid bridges in five-axis to get the correct detail from the machine. Without doing this, there’s a lot of hand work that needs to be implemented after it’s out of the machine to get it back where it needs to be. We always try to do the best we can with the machine so we’re not having to rely on the manual labor of going in and just redoing things the machine should have caught.”

While five-axis machines are currently the top of the line, there are times when they are overkill.

“We use five-axis machines for everything, as a milling center,” Ferguson says. “That being said, five-axis machines are not necessary for everything. For anything with your typical crown and bridge, five-axis machines are not really necessary because you really can attack anything from the top and bottom on a three-axis machine or even the three-plus-one or three-plus-two where you can angle the discs. A lot of labs that have five-axis machines, when it comes down to it, they’re not using it as a five-axis machine, which is fine. They’re getting results they really like, but, on the other hand, they’re buying a five-axis machine and realizing they don’t need to use that full functionality.”

The wild card: New 3D printing material

The process of and results from milling get better every day, but there’s new manufacturing technology that approaches production from an entirely different perspective-3D printing. Where milling is a reductive process, 3D printing is an additive process. 3D printing is currently only used for support applications, but the ambition is for it to be bigger.

“Printing models, surgical guides and other things were the beginning, but printing end-user parts, like temporary restorations, is where 3D printing needs to go,” says Avi Cohen, director of global dental at Stratasys.

“Most of what we’re printing is actually for implant cases from intraoral scans,” Ferguson says. “The doctor places a scan flag at the implant site, scans it with his or her intraoral scanner and, for us at Core3d, we’re actually working with, basically, every intraoral scanner available, whether it be CEREC, E4D, iTero, TRIOS, Carestream, 3M TrueDef-all of them. And we’re printing a model and putting a lab analog in that model. So then the lab can really do whatever it wants with it. It’s really keeping it right in the workflow it has always done. The technicians are most comfortable having their hands on what’s actually what’s going on, and, obviously, at that point, they’re able to decide what types of materials they want to use and whether they want to do a [milled] material, a pressed material or PFM porcelain build-up.”

Like milling, 3D printing is expected to get better with time, and Stratasys is already introducing more capable machines.

“We released another machine, called Dental Selection, at IDS this year that already enables you to create mixtures of colors so you can select any tooth color you want and the machine mixes the materials and prints the selected color,” Cohen says.

Many agree the future of CAD/CAM manufacturing is in 3D printing.

“I think printing, eventually in the future, will be the new method,” Faufau says. “I think once materials get developed for some newer products, that probably will be the manufacturing method for dental restorations in the future.”

“Printing the end-user part is where the future is going,” Cohen adds. “You go to the dentist or the lab, select what you want, press print and it prints for you. From a temporary restoration to final restoration, orthodontic appliances, anything you put in your mouth, even dentures, you put [what you need] into [the printer], select the colors of the patient and send the design to print.

“We are not there yet. There is a small step ahead to reach that.”

If 3D printing is to take off, it will require a level of market maturity we do not yet have.

“Not everybody has a scanner and the software and the vision,” Cohen says. “So it will take some time.”

But within a decade, Cohen expects 3D printing to be commonplace.

“This is the future,” Cohen says. “So 10 years from now, people will print everything they want. In 10 years, in the dental market, that was traditional for centuries, 10 years is around the corner.”

Digital materials are not part of every lab, but for those in which it is, the technology has streamlined workflows and only looks to get better.

Top photo: Lisa-Blue/Getty Images