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

Zirconia complete-arch fixed complete dentures are increasingly favored for the rehabilitation of edentulous patients due to their mechanical strength and esthetic qualities. Nonetheless, concerns persist regarding the risk of fracture, particularly in cases where restorative space is limited. This in vitro study investigated the compressive fracture resistance of zirconia superstructures with different occlusal-cervical heights (2mm, 4mm, and 6mm) when bonded to rigid titanium frameworks with cantilever extensions.

Thirty zirconia superstructures - Zirlux Transitions partially stabilized zirconia(35mm×10mm; heights: 2mm, 4mm, or 6mm) were bonded to standardized inverted T-shaped titanium frameworks (Grade 5, 35mm×10mm×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/min crosshead speed, 3mm 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.

Mean fracture loads were 2809.45±78.43N (2mm), 2895.60±104.49N (4mm), and 2892.30±76.54N (6mm), with no statistically significant differences (p > 0.05). 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.

Zirconia superstructures with reduced height (2mm) demonstrated compressive strength comparable to thicker designs when supported by a rigid titanium 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.