Wear of CAD/CAM ceramic inlays: restorations, opposing cusps, and luting cements

Six standard mesio-occlusodistal restorations in extracted mandibular human molars and six opposing palatal cusps from maxillary human first molars were prepared per group. The occlusal contact areas of the restorations and of the opposing enamel cusps were digitized with a three-dimensional scanner. The specimens were exposed to a clinically correlated long-term in vitro wear test. Dicor MGC, Cerec Vita Mk I porcelain, Cerec Vita Mk II V7R porcelain, and Cerec Mk II Vita V7K porcelain were tested. The mean wear of these ceramic materials at the end of the long-term test ranged from 24.3 +/- 10.3 microns (Cerec Vita Mk II V7R) to 88.0 +/- 37.3 microns (Dicor MGC). The mean wear of the opposing human enamel cusps ranged from 93.5 +/- 30.8 microns (Cerec Vita Mk II V7R) to 224.3 +/- 117.4 microns (Cerec Vita Mk I). All ceramic materials except Dicor MGC wore less than did previously measured standards, such as natural human enamel and amalgam. However, because the wear of opposing enamel cusps was high with Dicor MGC and with Cerec Vita Mk I the total wear of these two materials--the sum of the restoration's and the opposing tooth's wear--was higher than that of the standards. Only the new fine porcelain Cerec Vita Mk II V7R showed a total wear comparable to that of enamel, because of its moderate abrasivity against opposing enamel. The wear of the two luting composite resins was measured at the end of the test. Both luting composite resins wore more than did the ceramic inlays and surrounding enamel, leaving a shallow ditch around the restorations.