The effects of cyclic loading and preparation on the fracture strength of zirconium-dioxide implants: an in vitro investigation

Objectives: Zirconia is a potential material for the fabrication of oral implants. The aim of this study was to evaluate the effects of cyclic loading and preparation on the fracture strength of a zirconia implant system. Materials and methods: Forty-eight one-piece implants were divided into two groups of 24 implants: group A (without modification) and group B (1 mm chamfer preparation). Groups A and B were divided into three subgroups of eight implants each (1 = no artificial load, 2 = artificial load [98 N; 1.2 million loading cycles], and 3 = artificial load [98 N; 5 million loading cycles]). After completion of the loading, the fracture strength of each implant was determined in a universal testing machine. A two-way analysis of variance was used, the continuous response variable (fracture strength in Newtons) is modeled as a function of preparation, cycles, and the corresponding interaction as explanatory variables. Results: The mean fracture strength values obtained for the groups were: A1 (no preparation, no load) = 1928.73N, A2 (no preparation, 1.2 million cycles) = 2044.84 N, A3 (no preparation, 5 million cycles) = 1364.50 N, B1 (preparation, no load) = 1221.66N, B2 (preparation, 1.2 million cycles) - 967.11 N, and B3 (preparation, 5 million cycles) - 884.89 N. Fracture values were significantly different between subgroups A1 vs. A3 and B1 vs. B3. There was no significant difference between subgroups A1 vs. A2 and B1 vs. B2. Conclusions: Preparation as well as cyclic loading can decrease the fracture strength resistance of zirconia implants. Nevertheless, even the lowest values of mean fracture strength of the implants used in our study seem to withstand average occlusal forces even after an extended interval of artificial loading.