Effect of Implant Diameter on Biomechanical Response of Straight Multi-Unit Abutments in Mandibular All-on-3: A 3D Finite Element Study

Abstract

This study evaluates the biomechanical performance of varying implant fixture diameters in mandibular edentulous rehabilitation using the All-on-3 concept with straight multi-unit abutments. A three-dimensional finite element model of a mandible segment was constructed and subjected to static occlusal loading conditions derived from clinical bite force data. Three Brånemark-type implants with diameters of 3.75 mm, 4.0 mm, and 5.0 mm were analyzed using ANSYS Workbench to assess von Mises stress, equivalent strain, and factor of safety (FOS) in abutment and screw components. The results revealed that increasing the fixture diameter to 5.0 mm reduced von Mises stress by 12.8- 15.0% in abutments and 17-44.3% in screws across anterior and posterior positions. Similarly, strain decreased by up to 11.1% in abutments and 45.0% in screws. The highest FOS (37.48 for abutment, 25.09 for screw) was recorded at the 5.0 mm diameter, confirming enhanced safety margins. However, posterior implants experienced stress transfer from abutment to screw components as diameter increased, particularly due to local stiffness mismatch and cantilever effects. While all configurations remained below Ti-6Al-4V yield strength, the posterior 3.75 mm setup yielded the lowest FOS (1.45), suggesting a higher mechanical risk. These findings emphasize the need for careful diameter selection in posterior All-on-3 designs.