Biomechanical Analysis of Titanium Dental Implants in the All-on-4 Treatment with Different Implant–Abutment Connections: A Three-Dimensional Finite Element Study

The type of implant-abutment connection is one of the factors influencing the distribution of occlusal forces. This study aims to investigate the biomechanical performance of the mandibular all-on-4 treatment with different implant–abutment connections. Two connection types with 30° abutments and 18-mm implant fixtures were chosen for the posterior implants of the all-on-4 assembly. For the external hexagon connection (EHC) group, the implants with 4 mm in diameter were used. For the internal hexagon connection (IHC) group, we selected implants with 4.3 mm in diameter. A vertical force of 190 N was applied to the cantilever region. The FEA results indicated that the most stressed region in the two groups was prosthetic screws, followed by multi-unit abutments (MUAs). The lowest values of von Mises stress were both observed on the bone. The peak stress value of the implant screw and implant fixture in the EHC group were 37.75% and 33.03% lower than the IHC group, respectively. For stress distribution patterns, the load force tended to be concentrated at locations where components were interconnected. The EHC and IHC are clinically durable under the tested loading conditions, but the prosthetic screws and MUAs can be the weak point on the posterior implant within the mandibular all-on-four assembly. The peak stress values of implant screw and implant fixture in the EHC groups were lower than the IHC group.