Advanced crown and bridge design

The present article describes the CAD construction procedure of copings, reduced crowns, anatomical crowns, hybrid bridges, and other construction software features contained in the Digident dental CAD/CAM system (Girrbach Dental, Pforzheim, Germany). The individual design of a crown or a bridge framework will, of course, influence the stability and the longevity of the final dental restoration. Especially an anatomically reduced crown framework possesses--in comparison to a simple coping design--several advantages, while for some materials, a full crown design is esthetically not suitable. An anatomically reduced crown design results in a mechanical support of the occlusal cusps, as the high strength framework is mechanically more favorable than the veneering ceramics or composites. Moreover, the reduced construction of the anatomical shape allows the creation of ceramic layers of approximately homogeneous thickness. This has the effect that the residual stresses in the veneering ceramic after the thermal treatment, i.e., several firing and cooling cycles, are minimized. A prerequisite for the computer-aided anatomical construction of crowns is the inclusion of adjacent teeth and the articulation of the opposing jaw. In these terms, the opposing jaw or a bite impression have to be scanned, digitized, and positioned virtually in bite relation. While taking patient-specific articulator parameters into account, a software-integrated "virtual articulator" allows simulation of dynamic occlusion and therefore a computer-aided reduction of interfering contact points.