Stress Analysis in Edentulous Mandibular Bone Supporting Implant-Retained 1-piece or Multiple Superstructures

Purpose: The aim of this study was to investigate the stress distribution in mandibular bone supporting a single or separate multiple implant-retained superstructures. Materials and Methods: Three-dimensional finite element models consisting of the mandibular bone, 8 implants, and 1 or more superstructures were created. Vertical and oblique loads were directed onto the occlusal areas of the superstructures to simulate the maximum intercuspal contacts and working contacts, such as the canine-protected and group function occlusion. Results: The unseparated 1-piece superstructure generated the lowest maximum equivalent stresses in the peri-implant bone, followed by the 2-piece superstructure separated at the midline. For the 3-piece superstructure, which was separated between the canine and the premolar, the maximum stress was lower when the canine on the working side was loaded than when the posterior teeth were loaded. Discussion: Separating the 1-piece superstructure into 2- to 4-piece superstructures increased the mechanical stress around supporting implants. Canine load on the working side is distributed well in 1-piece and 3-piece superstructures. Conclusion: Based on the results of this finite element model study, canine protected occlusion is recommended for 1-piece and 3-piece superstructures. The unseparated superstructure was more effective in relieving stress concentration in the edentulous mandibular bone than the separated superstructures.