Influence of a Novel Spherical Connection Interface for Angled Abutments in Cantilever-Extended All-on-Four Bar Prostheses on Stress Distribution

In this study, the biomechanical performance of a newly developed spherical connection interface design for angled abutment systems used in all-on-four implant-supported bar-retained overdenture prostheses in completely edentulous patients was investigated. It is well known that bending moments generated in cantilever-extended prostheses lead to high stress concentrations in the implant, abutment, and surrounding bone tissue. In order to mitigate these adverse effects, novel abutment designs featuring a spherical connection surface were developed as an alternative to conventional 15° and 30° angled abutment models, and were evaluated in combination with two different bar cross-sections (I and UCG). The three-dimensional mandibular model was generated based on CT data, and the mechanical behavior of the prosthesis-implant-bone assembly was analyzed using the finite element method in the ANSYS Workbench environment. The models were assumed to be homogeneous, isotropic, and linearly elastic, and a 100 N occlusal load was applied in a 45° oblique direction. The results obtained according to the von Mises criterion demonstrated that the spherical connection designs provided a significant reduction in stress, particularly in the posterior region, compared with conventional models. In the I-section spherical model with 15° angulation, stress reduction of up to 23.2% was observed in the cortical bone surrounding the posterior implant, whereas the spherical models with UCG section demonstrated an improvement ranging between 24 - 27% in the posterior implant body. The findings indicate that the spherical interface design has the potential to reduce biomechanical risks associated with the cantilever effect and to enhance the service life of implant and superstructure components. This approach offers an innovative and clinically applicable solution for preventing complications related to the use of angled abutments.