Mechanisms of failure in porcelain-veneered sintered zirconia restorations

Abstract

The continuous increase in the demand for highly aesthetic and natural-appearing dental restorations and the development of strong ceramic materials has led to the adoption of sintered ceramics as new load-bearing components used in dental prosthetics. Zirconia is one of the most attractive restorative materials due to its advantageous mechanical properties and biocompatibility. Veneering porcelains are used to coat the surface of zirconia to enhance the aesthetic appearance of prostheses. Nevertheless, porcelain-veneered zirconia restorations are prone to failure primarily by the fracture of the veneering layers. In this paper, the nature of the interfacial bonding and failure modes on samples of broken porcelain-veneered sintered zirconia restorations were studied using Environmental Scanning Electron Microscopy (ESEM) with Energy-Dispersive X-ray (EDX) analysis. Typical fractographic features were observed in broken porcelain-zirconia prosthesis. The chipping mode fractures in the veneering porcelain indicated the dominance of the cohesive fracture mode, in agreement with clinical experience reported in the literature. The crack initiation and propagation within the veneered porcelain layer was also observed and analyzed by a further examination of the fractographic features on both the prosthetic samples and the fractured surface of porcelain zirconia bars. The result indicates that the crack initiated at the location of maximum stress (point of occlusal contact). In addition, it is surmised that the fragility of the prosthesis may result from the high Vickers hardness and the associated low toughness of porcelain.