Influence of all-on-4 implant angles on stability and crestal bone - A finite element optimization analysis

The all-on-4 implant technique is a restoration method designed for patients with complete or extensive edentulous, requiring only four implants to support a full-arch denture. However, the inclination angle configuration of implants directly affects force distribution and stability. Therefore, this study employs optimization techniques to investigate the impact of mesial and distal implant angle in mandibular all-on-4 cases on the biomechanics of bone tissue. This study established three-dimensional models of the mandible, implant, and framework. Finite element (FE) analysis was employed to simulate stress distribution and stability under various angular combinations. Force conditions were set to apply a 200 N vertical bite force at the left canine position and a 250 N oblique bite force at the left first molar position, simulating the maximum vertical and oblique loading scenarios during unilateral mastication. Optimal parameter settings were determined: the mesial implant inclination angle was set between −1.5° and 3°, and the distal implant inclination angle was set between 20° and 30°. The optimization technique identified the angular configuration that maximized bone stress uniformity and stability. Under a 200N vertical bite force, adjusting the implant angles from the original model's distal implant at 30° and mesial implant at 0° to optimized angles (distal implant 20°, mesial implant 2.8°) reduced crestal bone stress by approximately 4 %–12 %. Under a 250N oblique bite force, the optimized angles (distal implant 20.19°, mesial implant 2°) reduced crestal bone stress by approximately 4 %–16 %. Furthermore, the optimized angle can reduce the maximum displacement of the implant under 250 oblique force to 11 %. This study concluded that adjusting the angle of all-on-4 implants to approximately 2° for mesial implants and 20° for distal implants can maintain better stability and effectively reduce stress concentration around the implants.