Abstract
BACKGROUND: The purpose of this study was to use finite element analysis (FEA) to evaluate the mechanical effects of eight different anti-rotation structures in fin-type short implants based on the Bicon system under cyclic loading conditions. METHODS: Based on cone-beam computed tomography (CBCT) data, three-dimensional models of the maxillary posterior region and implant crowns were reconstructed and assembled with nine sets of fin-type short implant-abutment systems modeled using SolidWorks 2021. Finite element meshes were generated using 10-node tetrahedral elements (~ 2.41 million elements per model) in Hypermesh 2022, with mesh convergence verified to ensure computational error < 3%. Static structural analysis was performed in ANSYS 2022 with bonded contact conditions representing complete osseointegration. Three-stage loading (vertical, buccal-lingual 45°, lingual-buccal 45°) at 150 N was applied to simulate the masticatory cycle. RESULT: The unidirectional anti-rotation design exhibited the lowest peak stresses (cortical bone: 60.36 MPa, representing a 38% reduction versus baseline control; cancellous bone: 17.21 MPa, representing a 49% reduction; implant: 446.57 MPa, safety factor 1.97) and peak strains (cortical bone: 4409 µε; cancellous bone: 4779 µε, within the physiological adaptive remodeling range < 4000 µε). This design demonstrated superior mechanical strength with the highest safety margin against material yielding, improved structural stiffness with the lowest deformation under load, and optimal stress distribution characterized by reduced stress concentration and more uniform load transfer compared to other anti-rotation configurations. CONCLUSION: Finite element analysis revealed that among nine anti-rotation configurations evaluated, the unidirectional (single-sided) design exhibited optimal mechanical performance with 38-49% stress reduction in peri-implant bone tissue and the highest safety factor (1.97) in the implant component. For maxillary first molar short implant placement in cases of insufficient bone volume, adding a simple unidirectional anti-rotation structure to the Morse taper connection provides superior mechanical strength, improved stress distribution, and reduced risk of bone overload compared to either no anti-rotation structure or complex multi-sided configurations. These computational findings support the clinical selection of simplified anti-rotation designs for enhanced long-term stability in challenging anatomical scenarios.