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I 07 special _ CEREC I CAD/CAM 1_2010 This is particularly beneficial in the case of inlays, onlays, partial crowns and seriously weakened cusps. Prof Mörmann’s goal was to deploy CAD/CAM technology to create immediate all-ceramic resto- rations chairside without the need for temporaries. This goal derived from his experience that temporar- ilyrestoredinlaycavitieshaveasignificantlynegative influence on the integrity of the enamel. In many cases, the non-adhesively bonded temporary was positioned like a wedge in the cavity and transmitted the chewing forces to the weakened residual tooth. The applied forces also deformed weakly protected cusp walls. This resulted in cracks in the oral and vestibular enamel surfaces. A second goal was to make use of high-strength oxide ceramics, such as aluminium oxide (Al2O3) and zirconium oxide (ZrO2), and computer-controlled milling machines in order to create crown-and- bridge frameworks and hence pave the way for metal-free prosthetic treatment. Another recent development is the online trans- mission of intra-oral and extra-oral digital impres- sions and restoration design data to external dental laboratories,whichthenperformthemillingtasks.As a result, the dental laboratories are now more closely integrated into the work flow of dental practices. _Clinically proven All-ceramicchairsiderestorationsnumberamongst the most intensively researched dental treatment procedures. Numerous studies confirm that the clinical performance of inlays and onlays is at least comparable with that of cast-gold restorations. Durabilityisoneofthemostimportantevaluationcri- teria for ceramic materials. This underlines the im- portance of the study published in 2008 by Dr Tobias Otto (Aarau, Switzerland) that presented long-term clinicaldatagoingasfarbackas17years.2 Since1989, Dr Otto (one of the first CEREC users in Switzerland) has monitored 200 inlays and onlays produced using theCEREC1systemandfeldsparceramic(VITAMarkI). These restorations were placed in 108 patients in his dental practice between period 1989 and 1991. Heevaluatedhisfindingsonthebasisofthemodified USPHS criteria and summarised his clinical obser- vations after 10 years and 17 years, respectively. According to Dr Otto, 187 of the 200 restorations were still in place after 17 years. This was a survival rateof88.7%afteranaverageservicetimeof15years (Figs. 3–5). In other words, the annual failure rate was 0.75%.FailureswithCharlieandDeltaratings(USPHS) occurred between the 6th and 13th year. In most cases, these failures were attributable to ceramic fractures. The probability of survival was significantly higher than that of layered laboratory-produced ceramic inlays and was approximately equivalent to that of alternative long-term restorations, such as cast-gold inlays,whichhaveasurvivalrateof87%after20years andanannualfailurerateof0.7%.3 DrOttoestablished that 166 of the CEREC inlays (of an original basis of 200 restorations in 1991) were clinically intact. This is equivalent to a success rate of 83 % after an average servicetimeof15years.Thesurvivalratewassuperior to that established by Smales4 for cast inlays after 15years(lossrate:1.5%).Italsocomparesfavourably with the 1.3 % annual failure rate established for all- ceramic, non-CAD/CAM ceramic inlays.5 A contributing factor is that chairside ceramic inlays can be placed immediately in a single appoint- ment, thus eliminating the need for temporaries. In the case of conventional labside restorations, a temporaryisunavoidable.ProfRolandFrankenberger established that under the influence of chewing forces,thetoothissubjectedtotorsionalstressdueto the low elastic modulus of the temporary composite material. These forces can deform inadequately pro- tected cusp walls, cause partial fractures and incipi- ent enamel cracking, and weaken dentine adhesion. By contrast, the immediate placement of the ceramic inlay facilitates a contamination-free adhesive bond with the hard tooth tissue and stabilises weakened cusps.Thestabilisingeffectontheresidualtoothand theexistenceofanadhesivebondobviouslyoffsetthe consequences of wider adhesive gaps, as evidenced by long-term clinical findings.6 Fig. 2_Finite element measurement with the exertion of chewing forces: the ceramic inlay bears the chewing load; the tooth substance remains stress free (inlay is hidden). (Illustration: Prof Albert Mehl) Fig. 2