تاثير سماكة القلوب الزيركونية المصنعة بطريقة ال CAD/CAM في مقاومة التيجان للكسر (دراسة مخبرية)

Background& Objective: This study was carried out to test fracture resistance of crowns with Zirconia core made by CAD/CAM of two thicknesses, and test the influence of decreasing the core thickness on its fracture resistance, and study the patterns of failure. Materials & Methods: An acrylic tooth(shape of a lower molar)was prepared to receive full crown with a chamfer finish line(1mm).then we copied it into 24 metal replicas, then 24 ceramic crowns with Y-TZP Zirconia core were made, divided into two groups, (E4)12 crowns with 0.4 mm in core thickness,(E6)12 crowns with 0.6 mm in core thickness using Zirkodenta system of CAD/CAM. We veneer the crowns with 1 mm thickness of IPS emaxZirpress, we cemented the crowns with GIC, every abutment was placed into an acrylic base with a rubber layer. Fracture test was conducted applying a vertical force on the center of the occlusal surface using the general mechanical testing machine at the speed of 0.5 mm/min to the point of fracture, and the forces were recorded in N. The statistical analyses was conducted using T-student,Q2 . Then occurrence of the patterns of failure was studied p>0.05. Results: The mean value of the fracture force in group (E4) was 2115.33 N, and the 2855.67 N in group (E6). After the statistical study it was concluded that no significant differences between the two means were present, p>0.05.three patterns of failure were recorded, and no significant differences between them were present. Conclusions: There is no difference in fracture resistance between the core with 0.4mm thickness and the core with 0.6mm thickness in the crown made by CAD/CAM.