earticle

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Purpose: This study aimed to quantitatively compare the stress sensitivity of cortical and cancellous bones under varying preload torques and loading directions in zirconia abutment implant systems by finite-element analysis. Methods: A three-dimensional finite-element model of a mandibular implant system was developed, comprising a zirconia abutment, a Ti-6Al-4V screw and fixture, and surrounding bone structures. The model assumed complete osseointegration and linear elastic properties. Three torque conditions (10, 20, and 30 N·cm) and two loading angles (30° oblique, 90° vertical) with a 175 N occlusal force were applied. To assess stress sensitivity, maximum principal stress was measured in the cortical and cancellous bones across all scenarios. Results: The cortical bone consistently exhibited higher absolute stress values than the cancellous bone. However, the cancellous bone showed a markedly greater increase in stress between 20 and 30 N·cm torque, particularly under oblique loading (30°), with the stress increasing by >59.2%. In contrast, the cortical bone demonstrated a more gradual and linear stress response. Both bone types showed intensified stress concentrations at high torque levels and under oblique loading, suggesting increased mechanical vulnerability in the cancellous bone. Conclusion: The cancellous bone is more sensitive to preload torque and loading direction changes than the cortical bone in zirconia abutment systems. This finding underscores the need for cautious torque applications and stress-distributing prosthetic designs, particularly in areas with poor bone quality.