To tilt or supplement? Biomechanical comparison of tilted and extra-short implants in borderline atrophic mandibles: 3D FEA.

Abstract

This study aimed to evaluate the biomechanical effects of different posterior support strategies in borderline atrophic mandibular full-arch implant rehabilitation, where treatment decision-making remains challenging, using three-dimensional finite element analysis (FEA). A totally edentulous mandibular model was generated, featuring severe residual ridge atrophy posterior to the mental foramen, with barely sufficient bone height to accommodate extra-short implants superior to the inferior alveolar nerve. Three different implant configurations were analyzed: Model 1 consisted of axial implants combined with distal extra-short implants; Model 2 represented the conventional All-on-4 concept with tilted posterior implants; and Model 3 combined tilted posterior implants with distal extra-short implant support. Cortical and trabecular principal stresses, von Mises stresses in implant and prosthetic components, and prosthesis displacement values were evaluated under bilateral posterior loading. Model 2 demonstrated the highest stress concentrations and prosthesis displacement values in both peri-implant bone and prosthetic components. Cortical maximum principal stress values ranged between 6.54 and 9.85 MPa, while implant von Mises stresses ranged from 24.04 to 68.75 MPa. Prosthesis displacement values were highest in Model 2 (0.0273 mm). In contrast, Model 3 exhibited more homogeneous stress distribution and lower stress accumulation in cortical bone, trabecular bone, implants, abutments, and framework structures. Prosthesis displacement values in Model 3 (0.0053 mm) were comparable to Model 1 and substantially lower than those observed in Model 2The combination of tilted posterior implants with distal extra-short implant support demonstrated a more homogeneous stress distribution and lower prosthetic deformation under the simulated loading condition. These findings suggest that increasing posterior support may contribute to more favorable load distribution in borderline atrophic mandibular models.