Unstable cracking (chipping) of veneering porcelain on all-ceramic dental crowns and fixed partial dentures.

The central argument of this study is that residual stresses developed during the preparation of all-ceramic crowns and fixed partial dentures coupled with contact-induced cracking are the origin of the excessive chipping observed in clinical applications. The aim of this paper is to provide a simple basic analysis of the causes of residual stress development in ceramics and identify the key thermo-mechanical parameters responsible for these stresses and the resultant contact-induced failure. For simplicity, a bilayer planar geometry is considered. The key outcomes are the critical role of thermo-elastic properties and the thickness of the structures. The approach is then used to evaluate the propensity for unstable cracking of a range of crown structures, including substructures of a range of ceramics, and to show that two specific combinations are most prone to this behaviour, namely porcelain fused to glass ceramics and zirconia substrates. In addition, a simple approach for the minimization of the likelihood for such behaviour and chipping is proposed.