Communications of the ACM
Computers Aid Dentistry
New small-scale in-office CAD/CAM tools make it possible to go from preparing the tooth to fixing the permanent crown in a single visit.
Credit: MidtownDentalCareAssociates.com
Americans get fitted with 2.3 million dental crowns a year, according to the American College of Prosthodontists. Anyone who has had one knows the fitting of a dental crown is usually a lengthy, multistep procedure.
The standard process (once the tooth is prepared) starts with the dentist taking an impression of the tooth using a horseshoe-shaped tray filled with a putty-like substance. The impression is sent off to a laboratory that makes a model of the tooth from the mold, scans the model, and manufactures a crown to fit. It can take two to three weeks for the permanent crown to come back from the lab, and during that time the patient has to wear a temporary version, usually a cruder tooth-sized "cap." Finally, the patient returns to the office to have the permanent crown placed and reshaped as necessary.
New small-scale in-office CAD/CAM tools make it possible to go from preparing the tooth to fixing the permanent crown in a single visit. These Chairside Economical Restoration of Esthetic Ceramics (CEREC) systems rely on handheld 3D scanners, specialized computer-aided design (CAD) software, milling machines, and sintering ovens. Using such a system, a dentist can take a scan of the tooth, have the software model the crown and modify it as desired, and manufacture the actual restoration all in a few hours, without involving an outside lab.
How it started
The idea behind CEREC systems arose around 1980, when Dr. Werner Mörmann, a Swiss prosthodontist, reasoned that inlays could be produced in the dentist office by grinding them out of a block of ceramic. By 1985, working with Dr. Marco Brandestini, an electrical engineer, Dr. Mörmann had developed the first CEREC system, which entered clinical trials in 1987.
It is difficult to get a fix on how many CEREC systems are in use today. In 2014, CEREC ACCEPT, which offers training in the use of CEREC systems, claimed that more than 40,000 systems had been sold worldwide. One of the reasons it's hard to pin down the number of systems in use is that a CEREC system comprises multiple components that don't necessarily all come from the same vendor. "Not every manufacturer provides all devices for a CEREC workflow," according to Dentsply Sirona, a manufacturer of CEREC systems and an early partner of Dr. Mörmann. "We know that some practices use more than one scanner or milling unit, for example."
According to a Fortune Business Insights report on the dental CAD/CAM market in 2021, "The market is highly fragmented," with just a few major players accounting for most of the global market and other vendors active in specific regions or market segments. The report identified Key Companies in the sector as including:
- Align Technology, Inc. (U.S.)
- Dentsply Sirona (U.S.)
- Axsys Dental Solutions (U.S.)
- Medit Corp. (South Korea)
- Institut Straumann AG (Switzerland)
- PLANMECA OY (Finland)
- 3Shape A/S (Denmark)
- YENADENT (Turkey)
How it works
The CEREC process comprises several steps, some of which are the same as with traditional crown manufacture. First, the dentist prepares the tooth to receive the crown, by removing decay or performing a root canal, reinforcing portions of the tooth as necessary, and so on.
The next step is where the processes diverge. With a CEREC system, instead of taking a putty impression, the dentist uses a wand-shaped three-dimensional (3D) scanner to capture the geometry of the prepared tooth and, for complex restorations, the neighboring teeth.
CAD software running on a dedicated workstation (which Dr. Joel McFaul, a Dentsply Sirona CEREC system user, says the company described the workstation to him as a "high-end gaming PC") reads the scan and generates an initial model of the crown. The dentist can use the software to modify the crown, based on their experience and the individual patient's needs.
The final CAD model is then sent to a tabletop milling or grinding machine that whittles the crown from a metal or ceramic block. The last step in producing the crown itself is to use a small sintering oven to glaze and stain the material to match the color of the patient's other teeth. At that point, the crown is ready to be cemented into the patient's mouth, another place where the CEREC process is the same as the traditional approach.
Rather than taking those last two manufacturing steps in the office, it also is possible for the dentist to send the CAD data to an outside lab with a compatible system. That approach provides access to a wider range of possible shades for the crown and allows for producing more complex restorations. "We still send STL files to remote labs for bridges that are too big to fabricate in our office," says McFaul. "We can make bridges that replace two teeth, but for three or more, the bridge will be too long." The dentist can also export the images, or include them in a document to provide to the patient or to his/her insurance company.
Training
Not surprisingly, getting set up with a CEREC system represents a big investment of both time and money for the dentist. One source estimates a new system can cost upwards of $147,000. However, the savings from not using an outside lab can be substantial: an article on the Off the Cusp dental industry news site estimates that doing one implant and one bridge a week in-office with a CEREC system can save a practice about $2,000 a month.
Dentists also must undergo training to use the unfamiliar process. "My formal training came through online instruction, practical hands-on instruction in a dental simulation setting in Arizona, and in-office procedure instruction once the scan of the tooth had been obtained," recalls McFaul.
Other forms of chairside manufacturing may soon find a place in the dentist's office as well. Dr. Cord F. Stähler, chief senior vice president of Digital Platforms & Solutions and technology officer at Dentsply Sirona, recently told Dental Tribune, "A 3D printer could be a useful addition to the portfolio for use in applications in which milling and grinding machines do not always provide an optimum result — such as in the use of composites. I believe that 3D printing … is ready to become a part of the daily workflow for clinics and laboratories alike."
Jake Widman is a San Francisco, CA-based freelance writer focusing on connected devices, Smart Homes and Cities, Extended Reality, and other emerging technologies.
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