The Clean Alternative
Dental technology is forerunner of e-manufacturing for metal products.
Direct metal laser sintering (DMLS), a layer manufacturing process, first originated as a method of rapid tooling and rapid prototyping. It has advanced, via a multitude of innovations, to be the key technology for e-manufacturing, the fast and cost-effective direct production from electronic data. Sirona Dental Systems (Bensheim, Germany) uses laser sintering to manufacture customized series products out of metal. The firm has been producing dental prostheses in a special cobalt-chrome alloy, which has increased the efficiency of dental laboratories.
When Dr. Gunter Saliger goes to the dentist, his thoughts revolve around the issues of process optimization and materials development. And for a good reason—the physicist works in the CAD/CAM division at Sirona Dental Systems, one of the leading manufacturers in the field of dental technology. He is responsible for the production service infiniDent. The name represents a unique range of services offered in which Saliger and his eight-person team assume the role of extended workbench for dental laboratories throughout Europe. Since 2004, with modern technology and special production facilities, they have been making crown copings and bridges out of ceramic materials such as zirconium oxide and aluminum oxide on behalf of dental laboratory technicians. The fact that (since summer 2006) infiniDent's fabrication center can now manufacture dental prostheses out of metal in tantamount to a mini-revolution. This breakthrough has been made possible by a close collaboration with the German systems manufacturer EOS (Electro Optical Systems). The company, whose headquarters are located in Krailing, Bavaria, is one of the leading representatives of laser sintering technology. It delivers complete systems solutions to key industries such as the medical technology, aerospace and automotive. Originally, EOS machines were implemented for rapid prototyping and rapid tooling in the context of development processes. Today the trend is moving towards batch-sized optimized series production—e-manufacturing. In the area of plastics, laser-sintering based e-manufacturing is very much an established term. In the manufacture of metal parts it is just beginning to gain a foothold as a replacement process as a clean, efficient alternative to casting. And that is exactly the crucial point in the case of Sirona.
The End of Casting
While casting, with all its laborious pre- and post-processing, used to
be the only relevant molding process for metal dental prostheses,
dental laboratories can now choose laser sintering from the range of
services offered by infiniDent. "We are now virtually relieving the
dental laboratory technician of the messy part of the work. He no
longer needs to spend time mounting, embedding, casting or even
deflasking and cleaning a mold, but instead can concentrate on core
competences such as the ceramic veneering of the metal framework,"
explains Dr. Saliger. This framework—the anatomically static base of
construction of the dental prosthesis—is made at infiniDent's
fabrication center with the help of DMLS. Here, the EOSINT M 270
technology comes into use, processing a bio-compatible cobalt-chrome
alloy (inCoris NP), which EOS has developed specifically for dental
prostheses on the basis of input from the dental laboratory technicians
at Sirona.
Laser sintering is a layer of manufacturing process, which—depending on size and geometry—can economically manufacture small to large series. In this process, the products are directly built up 100 percent dense—without any molding tools whatsoever—in a generative process where layers of powder material are fused by a laser beam positioned via precision optics. The necessary technical control data for the laser technique are generated from geometric data using well-known 3D CAD programs such as SolidWorks, ProEngineer, Catia and AutioCAD.
Dental Direct Manufacturing
In dental technology, the control data comes from Sirona's CAD/CAM
system, inlab/inEos, which is widely used in dental laboratories in
Germany. This process-oriented, complete solution is made up of, among
other things, a modern 3D scanner (inEos) and an efficient 3D CAD
program (inLab 3D). The scanner digitizes the plaster castings made
from the individual patient's teeth impressions. Using the CAD program,
the dental laboratory technician (re)constructs the framework for the
metal prosthesis on-screen. The CAD data resulting from this is then
sent to infiniDent's fabrication center via Internet. One of Sirona's
technicians checks the received data for its completeness and prepares
it for laser sintering and then transfers it to the control unit of the
EOSINT M 270. Once there are a sufficient number of crown copings and
bridge frameworks for a job lot, the laser immediately starts
production. Layer-by-layer and in a period of only a few hours, the
machine produces several hundred dental prostheses out of the
cobalt-chrome powder. The built speed is approximately three minutes
per crown.
Up to and in excess of 80,000 units per year can be produced like this on a machine, whereby it is possible with laser sintering to produce bridges with up to six elements. And the delivery time from order receipt is just three days at most. Those are three days that the dental laboratory gains for processing further orders. "The throughput times decrease to a minimum through the use of laser sintering technology. That is comparable to an enormous increase in productivity and a definite technological advance for the dental laboratory," says Dr. Saliger. In comparison, while an experienced dental laboratory technician can produce about 10 crowns in one day, many hundreds of frameworks can be created on a laser sintering machine—always of the same consistently high quality. And they are made at an unbeatable unit price of only $25 each.
"There is currently nothing that can match the EOSINT M 270 as the technological heart of infiniDent's e-manufacturing process. From the point of view of cost-effectiveness, DMLS is way ahead of casting and even mechanical production," Dr. Saliger stresses.
The available capacity inside the machine (10 x 10 x 9 inches) provides sufficient space to built hundreds of crowns and bridges in one job lot. With layer thickness of only 20 micron and the precision-focused laser, even the most intricate of geometries and complex structures can be reproduced exactly. These are arguments which also make DMLS interesting for applications outside of medical technology. In many cases, the slight roughness of the parts' surfaces is a great advantage. For example, in the infiniDent process this improves the adhesion between the cobalt-chrome of the dental prosthesis framework and the subsequent layering with ceramic.
One-offs in Series
The Sirona example underlines the trendsetting significance of direct
metal laser sintering for the advancement of e-manufacturing in dental
technology. Yet, at the same time, the infiniDent project highlights
the really fascinating element of the process—the cost-effective
manufacture of series products of a very individual nature. After all,
no two dental prostheses are alike. But even though each part is
unique, it can be produced inexpensively and efficiently in series. For
this reason alone, laser sintering could become increasingly attractive
for many other specialist areas of medical and orthopedic technology.
The future role that the process will play, as an alternative for series production of metal parts in other industries, depends greatly on the development of different metal materials.
These will need to meet the ever-increasing demands in strength, temperature resistance and accuracy. Recognizing this dependency, EOS is working with industry to rapidly develop new materials. In September, stainless steel, a new DMLS material, came onto the market, and titanium will follow in the early part of 2007. Meanwhile, a number of developers are already conducting research into the next—currently secret—solution.
