Dentistry enters 3D digital world
Digital and dentistry are two words one doesn’t expect to hear in the same sentence. But if a company called KaVo has its way, the two words will be synonymous for dental technicians throughout the world.
Dental technicians traditionally rely on steady hands and expert eyes to prepare crowns, bridges, inlays, onlays, veneers and frameworks. Although they often are considered artists, the manual process is time-consuming, imprecise, and requires materials that might not provide the best durability or aesthetic appearance. 
A completed crown from KaVo’s Everest system.
From cars to crowns
KaVo, based in Leutkirch, Germany, is pioneering digital production of dental devices that saves time by automating the process and eliminating the need for adjustment. The new manufacturing process also enables superior materials to be used that are difficult or impossible to incorporate into the traditional manual process.
KaVo has adopted many of the digital design technologies traditionally used by auto and aerospace industries. But, the need for individualized products provides a unique challenge for the dental industry.
KaVo meets this challenge with a digital process that enables individualized dental devices to be designed and manufactured quickly in large quantities. The company’s turnkey dental system, called Everest, is based on the input and feedback of dental technicians who have worked for KaVo for more than 20 years. At the core of the system is software built for the dental industry by Geomagic, whose technology is used by manufacturers worldwide for mass production of customized devices, build-to-order manufacturing, and automatic re-creation of physical parts and molds.
Since its introduction in April 2002, about 120 Everest systems have been implemented under lease agreements in Europe, the U.S., New Zealand, Australia, China and Japan. Dental labs are able to conduct all work on site, providing greater control over production schedules and quality.
The fully digital Everest system enables individualized dental devices to be designed and manufactured quickly in large quantities.
The new process
Like any dental procedure, KaVo’s process begins in the dentist chair. If a crown is needed, for example, the patient’s cracked or damaged tooth is grinded, and a plastic impression made. The impression is sent to the dental lab, where a technician produces a stone master model. A crown made of wax is also created using conventional methods.
The Everest process starts with a 3D scanner that can capture a model of a tooth stump in about three minutes with an accuracy of 20 micrometers. The scanner looks like a microwave oven with a turntable that tilts. A single-button push sets the scanner in motion, capturing data from different angles to produce 15 point clouds.
The next step is to process the order through Everest control software, which is pre-installed in the computer connected to the scanner. There are four modules in the control software: scan, surface, CAD and CAM.
The scan module forms the user interface to the scan unit. With a few menu-guided steps, the operator can control the scan process for both stone and wax models. For the direct scan of production copings, KaVo uses special gypsum, which permits reflection-less exposure to guarantee reliable measurement without shiny surfaces. Scan data is automatically passed to the surface module.
The surface module incorporates a specialized version of Geomagic Studio software. The software, produced by Geomagic, a U.S. company based in Research Triangle Park, N.C., is the vital link in the customized manufacturing process. Geomagic software enables manufacturers to create an accurate digital representation of a physical part or object, and to tie together all the hardware and software required to produce individualized pieces in mass quantities.
In the case of a new crown, two data sets are imported into the surface module: The master model of the tooth stump, also called a die, and the wax model of the crown. The first step is to align the 15 different scans of the die relative to the surface of the crown and combine the die and the crown into the same orientation. This forms the basis of the mathematical surface calculation that is performed automatically. A preparation line is automatically detected on the die and the crown is cut according to the line. The die and the crown are then oriented and automatically adjusted so that there is minimum undercut.
All surfacing operations can be run automatically or interactively for operator-assisted modifications. Bridges are prepared in a similar process. Once the crown or bridge surface is prepared, the file is passed on to the CAD module.
The CAD module enables operators to design the final copings or bridges on the computer screen. The software automatically positions the digital model and trims it to the gum surface. The model can also be individually positioned or scaled. The finished design is now ready for the CAM module.
The CAM module automatically calculates the cutting data, taking into account processing properties specific to the material being used. The data is then transferred to the CNC system by way of an Ethernet connection or TCP/IP protocol.
The CNC system, called the Everest Engine, is a computerized five-axis cutting and grinding machine. Three axes define horizontal and vertical travel, while the two remaining axes define the pivot range of the clamping bridge and the rotational range of the spindle and tool. A double tool spindle and a pivotable clamping bridge do away with the need for tool changes during processing, and allow either four individual workpieces or two bridge constructions to be manufactured at one time.
For ceramic pieces, sintering of materials is the final step in the process, and is performed with a microprocessor-controlled thermal unit. Operators open the front door in an upward motion, load the pieces into firing trays, and place them inside. The thermal unit can be recalibrated by the operator and easily adjusted with a removable control device. Sintering takes about 12 hours.
When the process is complete, the finished piece is ready for the patients. No excess material needs to be removed, and the digital model guarantees a perfect fit.
Quality and precision
The digital process increases quality and precision, according to KaVo engineer Siegfried Gaile. When constructing crowns, for example, different layers of material traditionally had to be burned on top of one another. That layering method increased the chance of breakage. Using the Everest system, the material can be programmed to be appropriately homogenous, which lowers the risk that the crown will break in the mouth.
In addition to improving quality, the system gives technicians the ability to calculate exact measurements – an important factor in fitting dental pieces. In the case of a three-point bridge, connectors have to be placed between the copings on the left and right side of the crown. Measurements for those connectors must be precise to avoid breaking in the mouth – in the case of zirconium, for example, they must be a minimum of 9 mm².
“Conventional methods don’t allow for exact calculation, so technicians make estimations,” says Gaile. “But the mathematically derived definition of the digital model produced with the Everest system allows technicians to input desired measurements. They can rest assured that all connectors are correctly sized right down to the millimeter.”
Superior materials
The Everest System also opens the door for superior materials to be used, since it has few of the restrictions associated with manual casting and finishing. KaVo provides materials such as titanium for frameworks, leucite-reinforced glass ceramic, presintered zirconium oxide, and sintered zirconium oxide.
“The digital process enables us to use highly advanced materials that can’t be incorporated into conventional techniques,” says Martina Kürzinger, product marketing manager at KaVo. “The framework of a bridge, for example, can be made with a more attractive ceramic material rather than the traditional metal.”
A new glass ceramic used by KaVo can withstand 1,200 megapascals (MPa) or about 174,000 pounds per square inch. That’s more than sturdy enough to be used in the framework of bridges.
Threefold production increases
With digital dentistry, better quality and materials don’t come at the cost of productivity. Automation eliminates manual steps and inevitable human error, translating to as much as a three-fold increase in the number of high-quality pieces that a technician can produce in a given amount of time.
While conventional methods require about an hour to produce a titanium framework, the Everest system needs only 20 minutes. Production of a glass ceramic full crown takes nearly two hours with conventional methods, compared to less than 45 minutes with the Everest system. And, the finished product is made of superior materials.
Redefining digital dentistry
Continued development by KaVo will bring enhancements in the future that promise to make the process simpler and more automated, and that will result in dental pieces that are more precise in fit and more customized to the individual patient.
“We are constantly working to add new capabilities that will improve the process,” says Mohr. “Digital dentistry is in its infancy, but it’s already fulfilling its potential to dramatically improve the production process for technicians and to provide better end products for customers.”
