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: To investigate the effect of different degrees of mechanical wear on the spatial stress distribution of the Morse taper connection implant system, with a view to providing a theoretical basis for the clinical assessment of the long-term stability of dental implants.
METHODS: Three-dimensional finite element models of Morse taper implants with central screw thread wear levels of 0, 0.1, 1, 10, and 100 μm were established using SolidWorks software, and simulation analysis with Ansys Workbench software was performed. The implant models were inserted into artificial bone blocks (simulating type II bone, with a cortical bone thickness of 2 mm on the outer layer and cancellous bone inside). An alternating load of 300 N in the buccolingual direction was applied at the centroid of the abutment (forming an angle of 30° with the long axis of the implant). 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 were analyzed.
RESULTS AND CONCLUSION: (1) As the degree of mechanical wear on the central screw thread increased, the von Mises stress, principal stress, and strain in the implant and abutment also increased. The stress in the model was concentrated at the top of the implant, at the shoulder level of the implant, at the neck of the abutment, and at the bottom edge of the abutment. (2) Under moderate wear conditions (≥ 10 μm), the fatigue life of the implant system decreased by 30%, and the maximum von Mises stress of the central screw decreased by 37%, with the stress still primarily concentrated at the transition area between the head and the body of the central screw. (3) Under significant wear conditions (≥ 100 μm), the von Mises stress of the central screw decreased by 98%, with the stress concentrated at the screw head, and the fatigue life of the implant system decreased by 63%. Therefore, when the wear level of the central screw thread reaches ≥ 10 μm, the risk of screw loosening is significantly increased, and the fatigue life of the implant system is markedly reduced, warranting clinical attention.

Key words: dental implant, central screw, mechanical wear, screw loosening, mechanical complications, Morse taper, finite element analysis