The Influence of the Cervical Finish Line Designs on the Fracture Resistance of CAD/CAM Monolithic Zirconia Crowns, an in Vitro Study

Background: One of the most common problems of all ceramic restoration is their fracture tendency under occlusal and lateral forces. The effect of different margin designs on the fracture resistance of monolithic fully contoured zirconia crowns has not been widely investigated. Objective: This study conducted to compare the effect of two marginal designs namely Deepchamfer and Shoulder finish lines on the fracture resistance of Monolithic zirconia crowns. Materials and methods: An experimental study done by preparing two identical acrylic first maxillary premolars, one with deep chamfer margin (Group I) and the other acrylic tooth prepared with shoulder finish line design (Group II) then taking ten impressions using Polyvinyl siloxane impression for each group followed by pouring the impressions to construct 20 epoxy resin dies. Scanning each epoxy resin die, scanned data transferred to CAD/CAM machine (Laserdenta, Germany) to fabricate the crowns. Checking of seating and marginal adaptation of each crown on its corresponding die then each epoxy resin die was seated in an acrylic base to facilitate fracture resistance testing and cementation of the crowns to their corresponding epoxy resin dies using self-adhesive resin cement then fracture resistance testing was done using Universal testing machine (Instron, USA) and the load was applied at the center of each crown. Data were collected, tabulated and statistically analyzed. Results: Results showed that the highest fracture resistance values were recorded with Deep chamfer finish line. Conclusion: Within the limitation of our study the following conclusion were drawn: Finish line design has a significant effect on the fracture resistance of all ceramic crowns. Deep chamfer finish line has a significant effect on increasing the fracture resistance of Monolithic zirconia crowns.