High-tech tooth repair: incisive software may allow dentists to stop worrying about making a good impression

Science News, Dec 10, 1988 by Rick Weiss

High-Tech Tooth Repair

Dental researchers are planning a computer-driven revolution that they say could prove both pleasing for patients and profitable for the profession.

To date, the computer's role in the art of dental reconstruction has been largely limited to printing patients' bills and keeping track of their payments. With the advent of small, extremely powerful processors, however, a computer can get directly involved in patients' mouths as a designer and creator of dental prosthetics -- a prospect that is spurring both enthusiasm and controversy among dental professionals.

The application of computer-aided design and computer-aided manufacturing -- or CAD/CAM -- to dental prosthetics foreshadows a revolution in dentistry, researchers say. With its space-age hardware and sophisticated computer graphics, the new technology promises shorter, fewer and more pleasant office visits and an unprecedented flexibility in the types of materials used to make dental crowns, bridges and tooth-surface inlays.

While the Food and Drug Administration (FDA) has yet to approve the technology for use in the United States, a few European dentists already operate prototype dental CAD/CAM systems in their offices. These dentists can fit patients with custom-designed crowns in a single, one-hour office visit. The technique eliminates the need to make time-consuming, putty-like impressions of a patient's mouth, and so could change the dental laboratory's role in reconstructive surgery.

"The use of CAD/CAM for producing dental restoration represents the most sophisticated use of computers in dentistry so far," says Jack D. Preston of the University of Southern California (USC) School of Dentistry in Los Angeles, where a dental CAD/CAM system of French design is due to arrive in February for experimental use. Before long, software-designed prosthetics will become such an integral part of the profession that dental students will "grow up with [computers] like they grow up with the burr," Preston says.

For all the excitement over high-tech dental design, however, nettlesome problems persist. And the sparkling white promises of a new dawn in dentistry have reawakened an age-old dispute in the profession: What level of perfection is acceptable in oral reconstruction?

"Dentistry today is largely an art, and there is very little scientific rigor behind anything," says Reggie J. Caudill, a mechanical engineer at the University of Alabama in Tuscaloosa, who investigates dental applications of robotics and computer graphics. For decades, dentists have argued over exactly what constitutes a suitably snug dental prosthetic. The emergence of computerized engineering -- with its emphasis on high-precision specifications, or "specs" -- is forcing the profession to crunch some of its numbers anew.

Indeed, says Caudill, "probably what is going to be the biggest impact of all this technology on the field of dentistry is to move it from a qualitative, art-oriented profession to one that is based upon numerical rigor with some real definitions of what is a good fit."

The fundamental technique for making dental bridges and crowns -- permanent replacements for missing or damaged teeth -- has changed very little over hundreds of years. This "lost wax-casting" technique today takes at least two visits to the dentist's office, both generally requiring local anesthesia.

During the first visit, the dentist uses a burr (less accurately called a "drill") to grind down the outer layers of one or more teeth, leaving a reduced base upon which the permanent prosthetic will rest. After making a mold of that reduced surface with a putty-like, or "elastomeric," material -- a process prone to error -- the dentist fits the patient with one or more plastic or stainless steel temporary "caps." The patient wears these for about a week while dental laboratory technicians use the rubbery mold to cast a permanent replacement tooth from porcelain or metal.

On the second visit, after removing the caps, the dentist cements the cast crown or bridge permanently into place.

"Anyone who is working in dental CAD/CAM is basically working on the same philosophy: You want to automate making crowns," says Dianne Rekow, a CAD/CAM developer at the University of Minnesota Schools of Dentistry in Minneapolis. "The turnaround time can be much faster, you don't have to have a temporary, you don't have to have a second set of anesthesia, in theory it should fit much better, and you can do it all in one appointment -- all of which has a great deal of appeal."

Meeting this challenge with a computer requires an optical probe that can "read," or map, the detailed contours of a patient's prepared tooth base -- eliminating the need for impressions and casts of these spaces.

These probes trace the topography of a given tooth surface to generate a three-dimensional computer image. The topographic data are transmitted to a computerized, high-precision milling machine that uses an arsenal of small, rotary cutting tools to carve out the crown.