Abstract: BACKGROUND: Abutment screw loosening is one of the most common mechanical complications in implant restoration. Mechanical wear, as a potential cause of thread loosening, warrants attention due to its impact on mechanical performance and long-term stability. However, studies on the mechanical effects of thread wear in abutment screws remain limited, and no definitive conclusions have been reached. 
OBJECTIVE: This study investigates the effects of different mechanical wears on the internal connections of dental implants under dynamic loads, specifically looking at the spatial stress distribution within the implant system. The aim is to provide a theoretical foundation for the clinical assessment of the long-term stability of dental implants.
METHODS: Establish three-dimensional finite element models of Morse taper implant systems with central screw thread wear levels of 0, 0.1, 1, 10, and 100 μm using SolidWorks software, and perform simulation analysis with Ansys Workbench software. The implant models are inserted into artificial bone blocks (simulating type II bone quality, with a cortical bone thickness of 2 mm on the outer layer and cancellous bone inside). The buccolingual loading forces were 300 N obliquely (30°) respectively on the centroid of the abutment. The von Mises stress, principal stress, displacement, and fatigue life of the abutment, central screw, implant, and bone tissue in the five groups of models are analyzed.
RESULTS AND CONCLUSION: As the degree of mechanical wear on the central screw thread increases, the von Mises stress, principal stress, and strain in the implant and abutment also increase. Stress concentrations in the model are primarily located at the top of the implant, the neck of the abutment, the shoulder level of the implant, and the edge of the abutment base. Under moderate wear conditions (≥10 μm), the fatigue life of the implant system decreases by 30%, and the maximum von Mises stress of the central screw decreases by 37%, with the stress still primarily concentrated at the transition area between the head and the body of the central screw. Under significant wear conditions (≥100μm), the von Mises stress of the central screw decreases by 98%, with stress concentrated at the screw head, and the fatigue life of the implant system decreases by 63%. When the wear level of the central screw thread reaches ≥10μm, the risk of screw loosening significantly increases, and the fatigue life of the implant system is markedly reduced, warranting clinical attention.

Key words: Dental implant, Abutment screw, Mechanical wear, Thread wear, Screw Loosening, Mechanical complications, Morse taper, Implant stability, Finite element analysis (FEA)