Effects of implant diameter, insertion depth, and loading angle on stress/strain fields in implant/jawbone systems: finite element analysis.

PURPOSE To investigate the interactions of implant diameter, insertion depth, and loading angle on stress/strain fields in a three-dimensional finite element implant/jawbone system and to determine the influence of the loading angle on stress/strain fields while varying the implant diameter and insertion depth. MATERIALS AND METHODS Four finite element models were created, which corresponded to two implant diameters and two insertion depths. The jawbone was composed of cortical and cancellous bone and modeled as a linearly elastic medium; the implant had a detailed screw structure and was modeled as an elastic-plastic medium. Static loading was applied to the coronal surface of the implant with a maximum load of 200 N for all the models. Loading directions were varied, with buccolingually applied loading angles ranging from 0 to 85 degrees. RESULTS Increases in the angle of force application caused not only increased maximum stress/strain values but worsened stress/strain distribution patterns in the bone and implant. The maximum stress in the bone always occurred at the upper edge of the cortical bone on the lingual side adjacent to the implant. The use of a larger-diameter implant or an increased insertion depth significantly reduced the maximum stress/strain values, improved the stress/strain distribution patterns and, in particular, decreased the stress/strain sensitivity to loading angle. CONCLUSIONS A narrow-diameter implant, when inserted into jawbone with a shallow insertion depth and loaded with an oblique loading angle, is most unfavorable for stress distribution in both bone and implant. An optimized design of the neck region of an implant, in combination with a carefully controlled implant insertion depth that sets the threads of the implant neck well below the upper edge of the cortical bone, should be especially effective in improving the biomechanical environment for the maintenance of bone in implant/bone systems.