Biomechanical evaluation of cantilever length and arch form in the All-on-4 implant concept: a finite element analysis

BACKGROUND: This finite element analysis (FEA) was performed to evaluate the stress distribution and biomechanical performance of implants, cortical and trabecular bone tissues, and the titanium prosthetic framework in the All-on-4 implant concept. The aim of this study was to investigate the effects of different cantilever lengths and arch forms on the biomechanical behavior of these components. METHODS: Digital models representing an edentulous mandible were created in three different arch forms: square, oval, and triangular. In each model, two anterior parallel implants and two posterior tilted implants were placed within the All-on-4 concept. Full arch fixed prostheses with a titanium framework were designed on the implants. For each arch form, cantilever lengths were applied as follows: 5, 10, and 15 mm. To physiologically simulate masticatory forces, the foodstuff loading method was employed. Occlusal loads consisting of a vertical component of 150 N and an oblique component of 100 N were applied to the posterior region. Maximum von Mises stress values were calculated for the implants and titanium framework, whereas maximum and minimum principal stresses were analyzed in the cortical and trabecular bone tissues. RESULTS: In all arch forms, stress values obtained in the implant and titanium framework components under vertical loading were lower compared with those under oblique loading. In contrast, in the cortical and trabecular bone tissues, stress values observed under oblique loading conditions were lower than those under vertical loading. With an increase in cantilever length from 5 mm to 15 mm, stress values in the implant, framework, and bone tissues generally increased across all arch forms. Regardless of loading type, stress values were consistently lowest in the square arch form, followed by the oval and triangular arch forms. However, in the square arch form, higher maximum principal stress values were observed in the cortical bone in the 5 mm cantilever configuration compared with the 10 mm and 15 mm cantilever lengths. CONCLUSIONS: The biomechanical performance of the All-on-4 implant concept is influenced by arch form, cantilever length, and loading direction. Clinically, considering patient specific arch form and limiting cantilever length may reduce stress concentrations and support long term success.