Fracture resistance of premolar screw-retained implant-supported hybrid abutment crowns with monolithic restorations after thermomechanical aging

PURPOSE: This study evaluated the fracture resistance of premolar screw-retained implant-supported hybrid abutment crowns (HACs) fabricated from different monolithic restorative materials following artificial aging. MATERIALS AND METHODS: Forty-four titanium implant analogs were restored with HACs fabricated from four materials: 5 mol% yttria-partially stabilized monolithic zirconia (ST), strength-gradient multilayered zirconia (YM), lithium disilicate ceramic (LD), and resin composite containing dispersed nanoparticles (CM) (n = 11 per group). All specimens were subjected to thermocycling (10,000 cycles) and mechanical loading (1.2 million cycles) to simulate 5 years of clinical service. Fracture resistance was evaluated under compressive loading, and failure modes were analyzed using optical microscopy and scanning electron microscopy. Statistical analysis was performed using the Kruskal-Wallis and Steel-Dwass tests (α = 0.05). RESULTS: = 0.00033-0.0022). The YM group exhibited the highest median fracture resistance (2.06 kN, IQR: 2.00 - 2.60 kN), followed by ST (1.74 kN, IQR: 1.69 - 1.80 kN), LD (1.29 kN, IQR: 1.14 - 1.41 kN), and CM (0.87 kN, IQR: 0.79 - 0.92 kN). All specimens survived the artificial aging protocols. Distinct fracture patterns were observed depending on the restorative material, with zirconia-based groups showing more favorable resistance than resin composite. CONCLUSION: All tested HACs exhibited fracture resistance values exceeding maximum bite forces, supporting their clinical applicability. Strength-gradient multilayered zirconia demonstrated superior reliability after simulated 5-year aging, emphasizing its structural advantage and broader safety margin compared with other restorative materials.