Fracture resistance of zirconia fixed dental prostheses after low-temperature degradation and/or cyclic fatigue.

PURPOSE: Monolithic zirconia fixed dental prostheses (FDPs) are widely used because of their favorable esthetic and mechanical properties. Hydrothermal aging and cyclic fatigue may interact to affect monolithic zirconia FDPs, but evidence from anatomically shaped multi-unit restorations remains limited. This study evaluated fracture resistance, phase transformation, and failure characteristics of three zirconia restorative systems after simulated service exposure. MATERIALS AND METHODS: Ninety-six three-unit FDPs were fabricated from self-glazed zirconia (SG), De Corematrix zirconia (DZ), and Lava zirconia (LZ). For each system, the FDPs were divided into four exposure conditions (n = 8): control, cyclic fatigue, low-temperature degradation (LTD), and LTD followed by cyclic fatigue. All specimens were subsequently subjected to load-to-failure testing. Raman spectroscopy and scanning electron microscopy characterized phase transformation and microstructural features. RESULTS: All cyclically loaded FDPs survived 5 × 106 cycles without macroscopic failure. SG showed the highest control fracture resistance. Cyclic fatigue alone produced little change in SG, whereas LTD and combined exposure markedly reduced its fracture resistance. No exposure-related differences were detected for DZ or LZ, although equivalence was not established. Monoclinic-phase formation was not detected after cyclic fatigue alone but was observed after LTD in all systems and was greater after combined exposure. CONCLUSIONS: Simulated service exposure affected the zirconia restorative systems differently. SG exhibited the highest initial fracture resistance but was more susceptible to hydrothermal aging. For DZ and LZ, no differences were detected under the present sample size, but stability was not established. All tested FDPs tolerated clinical-level loads, even after long-term service simulations.