Digital design and fabrication in dentistry

Abstract

In the past three decades, the fast growing technology of Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) has been continuously developed and applied to many fields in engineering, manufacturing, entertainment, and medicine. While maturing in some of the fields, CAD/ CAM is still in developing stages in the medical and dental arena. From industry surveys, more than 240 million people are missing one or more teeth in North America, Europe and Japan. There are approximately 400,000 dentists in the United States and Europe, with 20,000 dental laboratories making over 40 million dental devices/restorations (crowns, bridges, implant restorations, dentures) each year to treat the patients (Nobel Biocare, 2005). Traditionally, dental restorations have been manually fabricated, which is a lengthy process. Initially, an impression of the patient?s mouth is made with a rubber-like material and a gypsum (plaster) model or cast, often called a stone model, is made from this impression. A wax pattern of the restoration is then created by manually adding wax to the stone model using small instruments with magnification. The completed wax pattern is then encased in a heat-resistant investment mold with the wax pattern burned out in an oven. Melted metal alloy is then cast into the mold to make the replacement tooth or restoration. This process, also called the ?lost-wax technique? is very labor intensive. Although the concept of CAD/CAMfor dentistry was advocated in 1970s by Francois Duret (Duret, 1988; Schmitt, 2001), the actual use of this computer automated design and manufacturing technology has been slow to evolve until lately. In the past, dental automation was difficult because the software and hardware needed for the automation was not fully reliable and too expensive. Today, advances in imaging, digital design, and solid freeform fabrication plus their increasing cost advantages have enabled CAD/CAM technology to become increasingly attractive compared to the traditional dental restoration practices. One of the major driving forces behind the transition to CAD/CAM technology in dentistry is the severe shortage of qualified dental laboratory technicians. There are at least ten different commercially available CAD/CAM systems for making dental restorations, and with the exception of one system all of them are laboratory-based.With this technology, many of the labor intensive steps of restoration fabrication are computer-based, allowing the technicians to focus on the more artistic aspects of the restoration process, such as adding the final layer of esthetic porcelain to the restoration framework. In the case of the office-based system, patients no longer need to make multiple visits to the clinicians, and there is no need for temporary restorations. However, the office-generated restorations are limited to simpler, one-tooth restorations, rather than more complex bridges used to replace missing teeth. This chapter describes and discusses digital technologies for design and fabrication of dental restorations including crowns, inlays, bridges, and dental bars for implant restorations. The remainder of this chapter is structured as follows. Section 8.2 provides an overview of commercially available dental CAD/CAM systems. Section 8.3 describes digital data acquisition methods by use of contact and non-contact digitizers. Section 8.4 presents techniques for surface reconstruction from the acquired digital data. Section 8.5 describes methods of digital design for standard teeth, inlays, and dental bars. Section 8.6 discusses digital fabrication processes including computer numerical control machining, rapid prototyping followed by investment casting, and direct digital manufacturing. © Springer 2008.