Medical

Dental Applications
One of the most well-known of all rapid manufacturing applications is Align Technology, Inc.’s InvisAlign™ orthodonture process. Stereolithography is used to make the tools to fabricate numerous clear plastic aligners which are worn sequentially by patients to move teeth into a desired final orientation.

Numerous rapid manufacturing approaches to the fabrication of dental restorations are commercially available or under development. These range from using a model generated by RP methods for casting dental materials, to the direct fabrication of the dental restorations themselves. As an example of the former, Cynovad Inc. (Canada) supplies equipment from 3D Systems on an OEM basis for use in dental laboratories. The agreement between the companies represented one of the largest sales ever made of additive fabrication equipment. 3D is now offering specially adapted versions of its ProJet system to make dental wax-ups.

Sirona Dental Systems’ InfiniDent service uses direct metal laser sintering (DMLS) technology from EOS GmbH to fabricate the metal framework of a bridge with up to six teeth from a specially-developed cobalt-chrome alloy. The starting point is a three-dimensional scan of a plaster casting of the patient's dental impression. The data set created from this is massaged by specialized software and subsequently sent to InfinDent’s fabrication center over the Internet. Once several hundred coping and bridge framework data sets are collected and checked, they're fabricated in a batch by the EOS machine in just a few hours.

The whole process takes just three days from start to finish and the building time of an individual crown works out to only three minutes. A single machine can make 80,000 or more units per year with great consistency, and at a cost of only about US$25 each. This contrasts sharply with the manual process which permits a trained technician to make only about ten crowns in an entire workday.

It's no longer necessary for technicians to mount, embed, cast, de-flask or spend much time cleaning the molded product. The frameworks emerge from the machine at full density and ready to be veneered with ceramic after very little finishing. The slight roughness of the sintered parts also works to good advantage in this application improving the adhesion of the ceramic.

Each RM approach seems to offer at least some unique and notable advantage. One example is the ability of Three Dimensional Printing to accurately match tooth color. It will be interesting to see how the competition among the technologies plays out. It’s also noteworthy that patent documents have begun to appear that describe techniques for the mass production of customized dental products. The progression is analogous to that followed by customized hearing-aid products, which are now largely made using RM.

Medical Devices...