Effect of distal cantilever and anterior implant diameter on framework and cortical bone stress in a PEEK-based All-on-Four mandibular prosthesis

Background Polyetheretherketone (PEEK) has been proposed as an alternative framework material for full-arch implant-supported prostheses due to its lower elastic modulus relative to metallic frameworks. However, quantitative data regarding the combined biomechanical influence of distal cantilever extension and anterior implant diameter in PEEK-based mandibular All-on-Four rehabilitations remain limited. Purpose To quantify the effects of distal cantilever presence and anterior implant diameter (3.5 mm vs. 4.5 mm) on framework stress and peri-implant cortical bone response in a PEEK-based mandibular All-on-Four prosthesis using three-dimensional finite element analysis. Methods Four implant configurations were modeled: Standard-NC (4.5 mm anterior, no cantilever), Mixed-NC (3.5/4.5 mm anterior, no cantilever), Standard-C (4.5 mm anterior, with cantilever), and Mixed-C (3.5/4.5 mm anterior, with cantilever). A 300 N static load was applied at premolar and molar positions under vertical (0°) and 30° oblique loading. Peak von Mises stress in the PEEK framework and crestal cortical bone, along with maximum principal cortical strain, were recorded. Results Distal cantilever extension increased peak framework stress by up to 59% under premolar vertical loading (222.24 MPa vs. 139.60 MPa) and increased crestal cortical stress by approximately 49% (18.36 MPa vs. 12.31 MPa) compared with the non-cantilevered baseline configuration. Under molar vertical loading, maximum principal strain increased by approximately 105% in the Mixed-C model compared to the Standard-NC configuration (0.0080 vs. 0.0039). Reduction of anterior implant diameter increased cortical strain by approximately 28–31% in non-cantilevered models and further amplified strain when combined with cantilever extension. Peak framework stresses reached 222.24 MPa in localized regions. Conclusion Distal cantilever extension was the primary determinant of biomechanical amplification in a PEEK-based mandibular All-on-Four prosthesis, while reduced anterior implant diameter exerted a secondary but additive effect. These findings highlight the mechanical sensitivity of low-modulus framework systems to cantilever geometry and implant diameter in full-arch rehabilitations.