A Photoelastic Study of Some Biomechanical Factors Affecting the Anchorage of Osseointegrated Implants in the Jaw

Photoelastic stress analyses of models of osseo-integrated oral implants were performed, comprising an investigation of the installation practice and load experiments. In the load experiments, single-threaded and unthreaded implants were loaded in horizontal and vertical planes. The results of the installation experiments showed that pre-tapping and careful screwing down of the implant reduced stresses in the test piece. When tightening the screw forcefully, high stress concentrations arose at the margin of the implant site. In the load experiments a threaded implant was analysed in three different anchorage situations: case A, illustrating complete bone anchorage up to the head of the implant; case B, vertical bone loss; and case C., horizontal bone loss. An unthreaded implant was also analysed. The results indicated only minor differences between the three anchorage cases in the vertical load experiments. However, the threaded implants displayed a more favourable stress distribution than the unthreaded one. In the horizontal load experiments high stress concentrations arose at the margin of the test piece on the compression side at minor load levels (98 N), Anchorage cases B and C showed the highest stress concentrations. The results have clinical relevance, both for installation practice and for the design of the oral implant bridge.