The influence of zirconia core designs on stress distribution in dental restorations: finite element analysis

Recently, substantial improvement in dental materials enables wide use of a variety of new systems in clinical dentistry. There has been a growing interest in all-ceramic materials due to their favorable esthetics and outstanding biocompatibility. On the other hand, it can be observed cohesive (chipping) and adhesive (delamination) failure on the all-ceramic crown. So as to decrease the occurence of this failure, veneer ceramic should be supported with zirconia coping against tensile stress. Some modifications in the coping design of all-ceramic crown can be made as it is done with the framework of metal fused to porcelain. With these modifications, the aim is to reduce the sress on the veneering ceramic. Three dimensional finite element analysis is a current technique for the measurement of stress amount and distribution. The aim of the current study was to evaluate and compare the amount of tensile stress in all-ceramic crown supported by different coping designs using finite element analysis. For this purpose, a morphologically accurate, large scale maxillary first premolar tooth model made with dental stone was scanned using smartOptics scanner. The models obtain as a result of scanning were compared to the morphological data on Wheeler's atlas and necessary changes were made. Using the VRMesh software, 4 models that have various buccal/ palatinal shoulder height and facet porcelain veneer were created. Loading conditions were determined and stress analysis were performed. The minimum tensile stress was observed in the zirconia crown with facet porcelain veneer. This design can be beneficial if aesthetic is not primary concern,. The stress decreased in the cervical area by increasing buccal and palatinal shoulder height. As the height of the buccal shoulder increased, tensile stress on the buccal cervical area decreased during the laterotrusive movement. The design that has 3 mm palatinal shoulder and 1 mm buccal shoulder was be effective in decreasing the stress on veneering ceramic.