Optimizing Strength in Full-Arch Restorations: Height Matters for Cantilevered Zirconia on Titanium Frameworks - An In Vitro Study

PURPOSE: To investigate the compressive fracture resistance of zirconia superstructures with different occlusal-cervical heights (2, 4, and 6 mm) when bonded to rigid titanium (Ti) frameworks with cantilever extensions. MATERIALS AND METHODS: A total of 30 zirconia superstructures-Zirlux Transitions partially stabilized zirconia (35 × 10 mm; height: 2, 4, or 6 mm)-were bonded to standardized inverted T-shaped Ti frameworks (Grade 5, 35 × 10 × 6 mm) featuring a 10-mm cantilever. Each assembly was screw-retained on implant analogs and subjected to vertical load until failure using a universal testing machine (1 mm/minute crosshead speed, 3-mm hemispherical tip). Fracture characteristics were examined under 50× magnification. The study was limited to static vertical loading and did not assess fatigue or lateral forces. RESULTS: Mean fracture loads were 2,809.45 ± 78.43 N (2 mm), 2,895.60 ± 104.49 N (4 mm), and 2,892.30 ± 76.54 N (6 mm), with no statistically significant differences (P > .05). The most frequent failure involved fracture of the prosthetic screw distal to the loading point. Two specimens in the 2-mm group showed superficial cracks, but no zirconia fractures or framework deformation occurred in any group. CONCLUSIONS: Zirconia superstructures with reduced height (2 mm) demonstrated compressive strength comparable to thicker designs when supported by a rigid Ti framework. These findings support the potential clinical use of such restorations in space-limited scenarios. However, further studies involving fatigue and multidirectional loading are necessary to validate clinical relevance.