In vitro evaluation of marginal adaptation and fracture strength of monolithic and double-layered zirconia ceramic crowns

Aim: The purpose of this study was to evaluate marginal adaptation and fracture strength of monolithic and double-layered zirconia ceramic crowns prepared by CAD/CAM method. Materials-Methods: 40 stainless steel dies representing prepared teeth were formed with CNC. The specimens had 6,5 mm height, 1.0 mm margin width (shoulder or chamfer) and 60 axial wall convergence angle. Crown samples (n=40) were divided into two experimental groups in two different margin configuration (n=20). Two experimental groups were divided into two subgroups as dental porcelain veneered on the zirconia copings and full contour (monolithic) zirconia crowns (n=10). Monolithic zirconia crowns were fabricated from Non-HIP zirconia blocks (Supra, Turkuaz Dental, İzmir) with CAD/CAM system. Zirconia copings were also prepared with the CAD/CAM sytem from Non-HIP zirconia blocks. Veneering material (IPS e.max Ceram, Ivoclar Vivadent, Schaan, Liechtenstein) was applied with the layering technique. All crowns were evaluated for marginal adaptation by using an optic microscope. Fracture strengths of crowns were measured by a universal testing machine at a speed of 0.5mm/minute after thermo-cycling at 5 oC -55 oC, 5000 times. All data were analyzed statistically. Results: Monolithic shoulder group showed the lowest values in marginal adaptation measurements (p<0.001). Monolithic zirconia groups showed the highest value of fracture strength (p<0.001). Conclusion: All groups showed clinically accepted values in marginal adaptation and fracture strength tests.