I digital dentistry _ CAD/CAM composite are ignored), the Kaplan–Meier survival rate was 89 % over the observation period. Dental adhesives were not yet available at the beginning of the study. If the patients are separated into two groups (that is, patients treated with and without the use of a dental adhesive), a significant difference is revealed. Without dental adhesive, the survival rate fell to approximately 80 % after 16 years; with dental adhesive, the survival rate was 90 %. The size of the filling did not play a role. Premolars performed better than molars. Vital teeth performed better then non-vital teeth. During the observation period, 122 events occurred. In 86 % of the cases, this resulted in the loss of the restoration. Fractures (39 %) were the most frequent reason for renewal.7 Similar findings were reported by Prof Gerwin Arnetzl. Between 1988 and 1990, Prof Arnetzl placed 358 two- and three-surface inlays made of Dicor, Optec, Hi-Ceram, Duceram and CEREC 1 (Mark I) using the adhesive bonding technique. The control group consisted of cemented gold inlays. After 15 years, CEREC and gold had a survival rate of 93 %. This was significantly higher than the equivalent figure for laboratory-produced sintered ceramic inlays, which had a failure rate of 32 %.8 Fig. 4 Fig. 3 Dr Reinhard Hickel and Dr Jürgen Manhart reviewed the scientific literature over a period of 10 years and calculated the annual failure rates of various materials used for Class I and II cavities. They found that CEREC restorations displayed 25 % fewer failures than cast-gold fillings.9 A particularly interesting investigation was carried out by Dr Anja Posselt and Prof Thomas Kerschbaum, who analysed the performance of 2,328 CEREC restorations placed in 794 patients in a dental practice.10 The survival rate after 9 years was 95.5 %. The filling size, tooth vitality, the prior treatment of caries profunda, the type of tooth and the location of the filling (separated according to upper and lower jaw) did not have any influence. The most common reasons for failure were tooth extractions (22.9 %) and fractures (17.1 %). Dr Andreas Bindl confirmed the suitability of chairside fabrication methods for anatomically sized CEREC crowns, milled and placed in a single visit.11 Various stumps were prepared for 208 feldspar ceramic crowns. After 5 years, 97 % (premolar) and 94.6 % (molar) of the conventionally prepared crowns (chamfer preparation) were still intact. Clinically short crowns with a reduced stump height achieved a survival rate of 92.9 % (premolar) and 92.1 % (molar), respectively. The failure rate for endo-crowns placed on premolars was significantly higher. Fig. 5 Fig. 3_Survival rate (according to Kaplan–Meier) of CEREC inlays and onlays: 88.7% after maximum of 17 years. (Source: Dr Tobias Otto) Fig. 4_Survival rate of one- to foursurface restorations (no significant difference) after maximum of 17 years. (Source: Dr Tobias Otto) Fig. 5_Survival rates of restorations on molars and premolars: CEREC restorations on premolars display a slightly higher success rate. (Source: Dr Tobias Otto) _CAD/CAM ceramics conform to the gold standard A further long-term study of the durability of CEREC restorations was published by Dr Bernd Reiss in 2006. In a private dental practice, 1,010 CEREC inlays and onlays were placed in 299 patients. After 15 to 18 years, 84.4 % of these restorations were still clinically perfect (Figs. 6 & 7). Up to the end point of the study (18.3 years), no further events were observed. If the retention of the restoration is seen as the sole criterion for evaluating survival (that is, if therapeutic procedures such as trepanation and subsequent margin corrections with the aid of 36 I cosmetic dentistry 4_ 2009