CAD/CAM - international magazine of digital dentistry

08 I I CE article _ practical lessons in CAD/CAM can be hypothesized that monolithic chairside milled IPS e.max may perform better. In a 10-year study, Kern et. al. found three-unit fixed partial dentures (FPDs) made from monolithic lithium disilicate ceramic showed five- and 10-year survival and success rates that were similar to those of conventional metal-ceramic FPDs.8 They con- cluded that for the monolithic lithium disilicate FPDs, the calculated survival rate was 100 per cent after five years and dropped to 90.8 per cent (when considering only catastrophic ceramic fractures) and 87.9 per cent (when considering catastrophic cera- mic fractures and biological failures) after 10 years.8 It is interesting to note that all catastrophic failures occurredinmolars.8 Single-unitmonolithicIPSe.max can be expected to perform better than FPDs in this study. Interestingly for both clinical studies mentioned, the restorations that were conventionally cemented performed just as well as those that were bonded.7,8 Therefore, assuming proper retention and resistance form has been achieved, it is acceptable to conven- tionally cement monolithic IPS e.max restorations. Because of the incredible flexural strength of IPS e.max, some clinicians were concerned that IPS e.max may be aggressive on the opposing den- tition.Inaclinicalstudy,Silvaet.al.foundIPSe.max to be more gentle on the opposing enamel than feldspathic ceramics with a wear rate on enamel similar to natural definition.9 Chairside CAD/CAM allows the clinician to predictably provide more conservative restorations, such as IPS e.max inlays and onlays, that have a longevity similar to full coverage crowns.10 The advantage to onlays over crowns is the conservation of healthy tooth struc- ture and subsequent prolonging of the tooth’s life cycle. Chairside milled onlays are an ideal restoration compared with direct resins. Despite their popu- larity, large posterior resin-based composite (RBC) restorations last only six to seven years.11,12 RBC restorations have poor clinical longevity, higher recurrent caries and greater need for replacement compared with the alternative, high-copper amal- gam.13–17 Amalgam and cast gold are not a popular option formanypatientsbecauseofaestheticconcerns,and an E4D onlay restoration is the ideal treatment for many patients who refuse these alternative treat- ments. Milled inlays and onlays have been shown to be very successful. Figs. 7–9_With the strength of IPS e.max, predictable restoration of second molars using the E4D Dentist System is possible. Figs. 10 & 11_In this case, a 37-yearold male presented with severe acid erosion and abrasion from gastroesophageal reflux disease and bruxism. CAD/CAM 3_2013 Fig. 8Fig. 7 Fig. 9 Fig. 11Fig. 10