In vitro failure of crowns produced by two CAD/CAM systems

Previous laboratory studies have demonstrated satisfactory fracture resistance of all-ceramic crowns placed using a resin-composite luting material and a dentine bonding system. This study investigated the fracture resistance of teeth restored using CAD/CAM technology, namely, Zirconia Based crowns and Cerec produced feldspathic porcelain crowns, both luted with a self adhesive resin luting material (RelyX Unicem Clicker 3M ESPE). Standardized preparations were carried out on two groups often sound, unrestored, maxillary premolar teeth. Ceramic crowns were constructed to have a thickness of 2mm at their midline fissure. Compressive fracture resistance was determined for each group using a Universal Testing Machine. The failure modes were also examined visually and interpreted according to a chosen scale. Mean Compressive fracture resistance of 746 (147)N and 1630 (175)N were recorded for the Cerec and Lava groups respectively; differences were statistically significant (p0.001). The fracture resistance of teeth restored with Lava crowns is significantly greater than a similar group of teeth restored with Cerec crowns.