Evaluation of stress distribution patterns of titanium, zirconia, and CFR-PEEK implants in mandibular all-on-four rehabilitation: a three-dimensional finite element analysis

In mandibular All-on-Four rehabilitation, posterior implant angulation is often dictated by anatomical constraints, while the mechanical properties of the implant–abutment system may influence load transfer to peri-implant bone and prosthetic components. This study aimed to evaluate the effects of posterior implant angulation and implant–abutment material on stress distribution in bone, implants, abutments, and connector screws using three-dimensional finite element analysis. Nine mandibular All-on-Four models were generated by combining three posterior implant angulations (15°, 30°, and 45°) with three implant–abutment materials: titanium, carbon fiber-reinforced polyetheretherketone (CFR-PEEK), and zirconia. Basal and occlusal connector screws were modeled as titanium in all models. Four loading scenarios were applied, yielding 36 linear static analyses. Maximum principal stresses were evaluated in cortical and trabecular bone, whereas von Mises stresses were assessed in the implants, abutments, and connector screws. Increasing posterior implant angulation generally increased maximum principal stresses in cortical and trabecular bone and von Mises stresses in the implant–abutment complex. Within each fixed angulation group, the CFR-PEEK models consistently exhibited lower bone, implant, and abutment stresses than the corresponding titanium and zirconia models. The highest implant and abutment stresses were observed in the 45° zirconia model (Model 9) under Loading Scenario 4, reaching 93.054 and 160.964 MPa, respectively. In contrast, connector-screw stresses were generally higher in the CFR-PEEK configurations. The highest occlusal- and basal-screw stresses were recorded in the 45° CFR-PEEK model (Model 6) under Loading Scenario 4, reaching 46.565 and 138.168 MPa, respectively. Within the assumptions of the static finite element model, material selection redistributed mechanical demand among the evaluated components rather than uniformly reducing it. CFR-PEEK produced lower stresses in bone, implants, and abutments at each posterior implant angulation but generally increased stress in the titanium connector screws. Consequently, no material was uniformly optimal across all evaluated components. When anatomical constraints necessitate a 45° posterior implant, the potential stress-reducing effect of CFR-PEEK on bone and the implant–abutment complex should be weighed against the accompanying increase in connector-screw stress. Clinical and fatigue-based validation is required before material-specific recommendations can be made.