Durability of zirconium dioxide ceramic restorations with masticatory simulation

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The purpose of the present study was to evaluate the durability of zirconium dioxide (ZrO_2) ceramic restorations by investigations of adaptation and fracture resistance.The first investigation evaluated the adaptation and fracture resistance of anterior single-tooth ZrO_2 ceramic copings or crowns with three different finish line designs (shoulder, rounded shoulder, and chamfer). The finish line design may have no effect on marginal adaptation of single-tooth ZrO_2 ceramic copings and crowns. The marginal and internal adaptation values observed in the present study were all within the range of clinically acceptable standards. The firing procedure did not affect the marginal and internal adaptation of ZrO_2 ceramic restorations. No influence of finish line designs on the fracture strength of ZrO_2 ceramic restorations was demonstrated. Some chipping of veneering porcelain and fracture at the interface between ZrO_2 ceramics and veneering porcelain were observed during the aging simulation.The second investigation examined the influence of different convergence angle (6°, 12°, and 20°) or cement space (10 μm, 30 μm, and 60 μm) on adaptation of posterior single-tooth ZrO_2 ceramic copings. Both the median values of marginal discrepancy (27-43 μm) and internal space width (54-70μm) in all groups were within the clinical acceptable range. For the groups of cement space 60 μm, the convergence angles significantly influenced on the marginal adaptation. The internal space values in the groups of convergence angle 20° was significantly smaller compared to the other groups.Further investigations will be necessary to evaluate the durability of ZrO_2 ceramic restoration with different experimental designs. Furthermore, clinical evaluations would be necessary to validate the results of the present study.