I digital dentistry _ CAD/CAM CAD/CAM expands the scope of restorative dentistry Author_ Manfred Kern, Germany Owing to the high degree of polymerisation shrinkage, these inlays required extensive machining, did not fit exactly to the inner surfaces, and displayed large tolerances at the margins. In addition, Prof Mörmann wished to use ceramic on account of its similarity to natural enamel and dentine. Only with the aid of computer-controlled profile-grinding and milling machines was it possible to mill silicate ceramics (and later oxide ceramics) subtractively for highly aesthetic restorations—restorations that displayed constant and reproducible material characteristics, as well as scope for cost optimisation. The broad acceptance of dental CAD/CAM procedures is evident from the more than 20 million all-ceramic restorations (chairside plus labside) that have been produced worldwide. _Adhesive bonding furthered the development of CAD/CAM restorations Two factors played a role here. The first factor was the desire of proponents of computer-aided chairside restorations to machine an industrially manufactured silicate ceramic with defined physical characteristics directly adjacent to the chair, and treat the patient in a single visit, without the need for a temporary. The second factor was the introduction of adhesive bonding, which creates a force-locked link between the ceramic restoration and the residual tooth tissue, does not display a mechanical interface and hence prevents crack-inducing tensile stresses. Since the introduction of adhesive bonding, it has been possible to apply defect-oriented and substance-conserving preparation techniques. The combination of CAD/CAM ceramics and adhesive bonding facilitated the permanent stabilisation of seriously weakened cusps (Fig. 2). It was possible to dispense with mechanical retention in the cavity geometry because adhesive bonding guarantees an intimate link with the residual tooth. In many cases, a partial ceramic crown eliminated the need for a metal-based crown. This latter type of crown has the disadvantage that it necessitates a circular preparation (and hence the loss of healthy tooth tissue) in order to achieve the necessary retention. The mechanical strength of individually machined silicate ceramics is transferred directly to the tooth tissue. Fig. 1 Fig. 1_Prof Werner Mörmann and Dr Marco Brandestini in 1985 with the CEREC 1 prototype. (Photo: Prof Werner Mörmann/ Quintessenz) _Today, it is impossible to imagine dentistry without digital technology and CAD/CAM procedures. Intra-oral and extra-oral measuring, the scanning of antagonists and bite registrations, 3-D design on a computer, the availability of countless tooth shapes in a dental database, the creation of anatomically shaped occlusal surfaces, functional articulation on a virtual model, the subtractive machining of high-performance ceramics—all this would be impossible without computers. The groundwork for this quantum leap was laid in Switzerland in 1985. For the first time ever, a 3-D optical impression of a prepared tooth was acquired using an intra-oral video camera (triangulation measuring technique) and then transferred to a computer.1 Using a computer, special imaging software and a CNC milling unit, Prof Werner Mörmann and Dr Marco Brandestini from Zurich University created the first CAD/CAM inlay from a silicate ceramic material (Fig. 1). This development was occasioned by Prof Mörmann’s unpromising experiments with occlusionborne composite inlays as a substitute for amalgam. 34 I cosmetic dentistry 4_ 2009