Simulation of clinical fractures for three different all‐ceramic crowns

Comparison of fracture strength and fracture modes of different all‐ceramic crown systems is not straightforward. Established methods for reliable testing of all‐ceramic crowns are not currently available. Published in‐vitro tests rarely simulate clinical failure modes and are therefore unsuited to distinguish between the materials. The in‐vivo trials usually lack assessment of failure modes. Fractographic analyses show that clinical crowns usually fail from cracks initiating in the cervical margins, whereas in‐vitro specimens fail from contact damage at the occlusal loading point. The aim of this study was to compare three all‐ceramic systems using a clinically relevant test method that is able to simulate clinical failure modes. Ten incisor crowns of three types of all‐ceramic systems were exposed to soft loading until fracture. The initiation and propagation of cracks in these crowns were compared with those of a reference group of crowns that failed during clinical use. All crowns fractured in a manner similar to fracture of the clinical reference crowns. The zirconia crowns fractured at statistically significantly higher loads than alumina and glass‐ceramic crowns. Fracture initiation was in the core material, cervically in the approximal areas.