Fatigue Survival and Biomechanical Behavior of Two-piece Titanium and Zirconia Dental Implants

Background: Titanium implants are considered the gold standard for oral rehabilitation; however, zirconia implants have emerged as a metal-free alternative with promising esthetic and biological properties. Despite these advantages, limited evidence is available regarding their long-term fatigue behavior and fracture resistance. Materials and Methods: In this in vitro experimental study conducted at São Paulo State University (UNESP), Brazil, forty implants were divided into two groups (n = 20): zirconia implants (ZZ) and titanium implants (TZ) (4.1 × 10 mm). Implants were embedded in polyurethane blocks according to ISO 14801:2016 specifications. Monolithic zirconia crowns were fabricated using CAD/CAM technology and cemented onto zirconia abutments. All assemblies underwent thermomechanical aging (2×10⁶ cycles, 200 N, 2 Hz). Fatigue resistance was assessed using a stepwise loading protocol. Crown–abutment misfit was measured microscopically, and torque loss after fatigue was recorded. Statistical analysis was performed using Mann–Whitney U tests and Kaplan–Meier survival analysis (α = 0.05). Results: Zirconia implants showed significantly greater fracture resistance (1123.73 ± 153.61 N) than titanium implants (818.67 ± 42.41 N) (p = 0.037). No significant difference in fatigue survival was observed between groups (p = 0.097). The zirconia group presented greater crown–abutment misfit (39.63 ± 10.1 μm) than the titanium group (25.09 ± 4.6 μm) (p < 0.001). Catastrophic implant body fractures were more frequent in the zirconia group, whereas titanium implants exhibited more repairable failure modes. Conclusions: Zirconia implants demonstrated similar fracture resistance but showed catastrophic implant fractures, whereas titanium implants presented repairable failure patterns.