Influence of implant length and bicortical anchorage on implant stress distribution.

BACKGROUND: Short implants present superior failure rates for everybody.

PURPOSE: The aim of this theoretic study was to assess to what extent implant length and bicortical anchorage affect the way stress is transferred to implant components, the implant proper, and the surrounding bone.

MATERIALS AND METHODS: Stress analysis was performed using finite element analysis. A three-dimensional linear elastic model was generated. All implants modeled were of the same diameter (3.75 mm) but varied in length, at 6, 7, 8, 9, 10, 11, and 12 mm (Brånemark System, Nobel Biocare AB, Gothenburg, Sweden). Each implant was modeled with a titanium abutment screw and abutment, a gold cylinder and prosthetic screw, and a ceramic crown. The implants were seated in a supporting bone structure consisting of cortical and cancellous bone. An occlusal load of 100 N was applied at a 30 degrees angle to the buccolingual plane.

RESULTS: With the selected model and bone properties, the coronal cortical anchorage was dominating, and the bone stress concentrated to that area.

CONCLUSIONS: The maximum bone stress was virtually constant, independent of implant length and bicortical anchorage. The maximum implant stress, however, increased somewhat with implant length and bicortical anchorage.