Abstract: BACKGROUND: The long-term effect of All-on-4 implant fixed denture is closely related to biomechanics. Its occlusion design affects the stress distribution of every part of the restoration. However, there is limited and inconclusive biomechanical research on All-on-4 implant fixed denture both domestically and internationally so far. 
OBJECTIVE: To analyze the effect of different occlusal contacts on the stress distribution of mandibular All-on-4 implant fixed denture. 
METHODS: A model of mandibular All-on-4 implant fixed denture was established. By changing the loading force, direction, and position, 10 loading conditions were set up to simulate centric occlusion, laterotrusive occlusion, and protrusive occlusion. The stress distribution and maximum stress values of every part of the model in different loading conditions were analyzed and compared among each group of models by loading different tooth positions to simulate different occlusal contact types.
RESULTS AND CONCLUSION: (1) The stress distribution cloud diagrams of each group of models were basically similar. The stress of the implant was mainly concentrated at the implant neck. The stress of the surrounding bone tissue was mainly concentrated around the implant neck, and the stress of the cortical bone was significantly higher than that of the cancellous bone. The stress of the abutment was mainly concentrated at the connection between the abutment and the implant and the abutment and the upper restoration. The stress of the titanium bracket in the upper restoration was mainly concentrated at the connection between the abutment and the titanium bracket, and the stress of the resin surface in the upper restoration was mainly concentrated on each loading point. (2) In simulating centric occlusion, the maximum stress value of the implant significantly increased when the cantilever was not loaded. It indicates that the mandibular All-on-4 implant fixed denture can have occlusal contact in the distal cantilever during centric occlusion. (3) In simulating laterotrusive occlusion, the maximum stress values of every part of the model significantly increased when simulating canine-guided occlusion. The maximum stress value of the simulated laterotrusive balanced occlusion was slightly lower than that of the simulated group functional occlusion. It indicates that group functional occlusion can be selected in the permanent prosthesis after osseointegration and laterotrusive balanced occlusion can be selected in the provisional restoration of mandibular All-on-4 implant fixed denture. (4) In simulating protrusive occlusion, the maximum stress values of every part of the model significantly increase when only the front tooth is loaded. In simulating protrusive balanced occlusion, the maximum Von-Mises stress value is relatively small. It indicates that the protrusive occlusion of mandibular All-on-4 implant fixed denture can choose protrusive balanced occlusion.

Key words: finite element analysis, All-on-4, occlusal contact, stress distribution, implant restoration, engineered dental material