The effect of crown length on the fracture resistance of posterior porcelain and glass-ceramic crowns.

This in vitro study measured the changes in the fracture resistance of posterior crowns as a function of crown length. The crowns, 10 for each group, were made of a feldspathic porcelain (Ceramco), a glass-ceramic material (Dicor), and an alumina-reinforced glass (In-Ceram). Three different crown lengths were tested on acrylic resin dies. The restorations were fractured in a testing machine using a steel ball, 12.7 mm in diameter, that contacted the occlusal surface at three distinct points. Statistical analysis was performed using the Weibull distribution. The fracture resistance increased significantly with increasing crown length for all crown materials.