The influence of design parameters on the FEA-determined stress distribution in CAD-CAM produced all-ceramic dental crowns.

INTRODUCTION Knowledge of factors, which influence stress and its distribution is of key importance to the successful production of durable all-ceramic restorations. The objective of this study was to evaluate, by finite element analysis (FEA), the influence of the shape of the preparation and the cement layer on the stress distribution in CAD-CAM produced all-ceramic crowns and in their cement layer. MATERIAL AND METHODS The CAD models of multi-layer all-ceramic crowns for posterior tooth 46 of three patients produced with CAD-CAM-technology were translated into a three-dimensional FEA program. The stress distribution due to the combined influences of bite forces, residual stresses caused by the difference in expansion coefficient of the two ceramic layers, and the influence of shrinkage of the cement was investigated. RESULTS The tensile stresses in the crown for the chamfer knife-edge preparation might put the integrity of the currently available ceramic materials at risk, while a non-uniform cement layer might result in stresses exceeding the bond strength. It was concluded that for long lasting restorations in the posterior region it is advisable to make a chamfer with collar preparation, the cement layer as uniform, and the difference in thermal expansion for the two ceramics as small as possible. SIGNIFICANCE This study indicates that for full ceramic crowns in the posterior region, specific design rules should be followed, and that FEA utilizing CAD-CAM data can be a successful tool to develop design guidelines for all-ceramic restorations.