Stress distribution in the abutment and retention screw of a single implant supporting a prosthesis with platform switching.

PURPOSE Three-dimensional finite element analysis was conducted to evaluate and compare the stress distribution in the abutment and retention screw of implant-supported single crowns with platform switching and with a conventional platform under vertical and oblique loading. MATERIALS AND METHODS Two finite element models were created simulating an osseointegrated implant (4 × 10 mm, platform 4.1 mm) embedded in jawbone. One model simulated a 4-mm-diameter abutment connection (conventional model) and the other represented a 3.8-mm-diameter abutment connection (platform-switched model). A crown with a cobalt-chromium framework and feldspathic porcelain veneering was applied to the titanium abutment. Static vertical and oblique loads were applied to the crown, with a maximum load of 150 N. RESULTS In both models, the highest stress values occurred in the abutment during vertical and oblique loading. Nevertheless, the von Mises stresses in the abutment and the retention screw were lower in the platform-switched model than in the conventional model. During axial loading, the abutment and screw supported slightly less stress in the conventional model than in the platform-switched model. Increases in the angle of force application caused a progressive increase in stresses in the abutment and screw in both models. The maximum stress was distributed at the margin and transgingival area of the abutment and on two-thirds of the flat area and the first threads of the retention screw in both models. CONCLUSIONS Platform switching reduced the stress values on the abutment and retention screw of a single-unit prosthesis during oblique loading. Regardless of whether platform switching was employed, the stress on the abutment and screw gradually increased as the loading direction changed from vertical to 45 degrees oblique. The locations and distributions of stresses were similar in both models.