CAD0110

Fig. 1_Prof Werner Mörmann and Dr Marco Brandestini in 1985 with the CEREC 1 prototype. (Photo: Prof Werner Mörmann/ Quintessenz) 06 I I special _ CEREC _Today, it is impossible to imagine dentistry without digital technology and CAD/CAM proce- dures.Intra-oralandextra-oralmeasuring,thescan- ningofantagonistsandbiteregistrations,3-Ddesign on a computer, the availability of countless tooth shapes in a dental database, the creation of anatom- ically shaped occlusal surfaces, functional articula- tion 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 op- ticalimpressionofapreparedtoothwasacquiredus- ing an intra-oral video camera (triangulation meas- uringtechnique)andthentransferredtoacomputer.1 Using a computer, special imaging software and a CNCmillingunit,ProfWernerMörmannandDrMarco Brandestini from Zurich University created the first CAD/CAM inlay from a silicate ceramic material (Fig. 1). This development was occasioned by Prof Mörmann’sunpromisingexperimentswithocclusion- borne composite inlays as a substitute for amalgam. Owingtothehighdegreeofpolymerisationshrink- age,theseinlaysrequiredextensivemachining,didnot 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 lateroxideceramics)subtractivelyforhighlyaesthetic restorations—restorations that displayed constant and reproducible material characteristics, as well as scope for cost optimisation. The broad acceptance of dentalCAD/CAMproceduresisevidentfromthemore 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 thedesireofproponentsofcomputer-aidedchairside restorations to machine an industrially manufac- tured silicate ceramic with defined physical charac- teristics directly adjacent to the chair, and treat the patient in a single visit, without the need for a temporary.Thesecondfactorwastheintroductionof 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 sub- stance-conserving preparation techniques. ThecombinationofCAD/CAMceramicsandadhe- sive 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 thedisadvantagethatitnecessitatesacircularprepa- ration (and hence the loss of healthy tooth tissue) in order to achieve the necessary retention. The me- chanical strength of individually machined silicate ceramics is transferred directly to the tooth tissue. CAD/CAM 1_2010 CAD/CAM expands the scope of restorative dentistry Author_ Manfred Kern, Germany Fig. 1