Finite element analysis of effect of prosthesis height, angle of force application, and implant offset on supporting bone

Purpose: This finite element analysis was conducted to determine the magnitude of stress in the supporting bone when implants were arranged in either a straight-line or an offset configuration. In addition, the effects of axial and nonaxial loading and changes in prosthesis height were assessed. Materials and Methods: An 8-node hexahedral solid-element 3-dimensional finite element analysis model of the mandible was created using PATRAN software. Three titanium endosseous implants were placed in the model 7 mm apart. The center implant was placed on the line from the centers of the terminal implants (no offset), 1.5 mm lateral to this line (1.5-mm offset), or 3.0 mm lateral to this line (3.0-mm offset). Forces of 200 N were applied to a point corresponding to the center of the middle implant when the implants were in a straight-line configuration. Forces were applied in a straight vertical direction or in 15-degree increments to the vertical to a maximum of 60 degrees. Simulated type IV gold prostheses were made to simulate heights of 6 and 12 mm. Results: The least stress in the supporting bone was found with vertical loading of the no-offset implants with the 6-mm prosthesis (3.12 MPa) followed by the same alignment with the 12-mm prosthesis (3.86 MPa). Changing the angle of force application by 15 degrees resulted in increased stress to the underlying bone, and the creation of an offset did not fully compensate for this increased stress. Discussion: In contrast to previous studies, this study examined 3 elements not previously studied together in a single finite element analysis, using the maximum offset defined by normal anatomic contours of mandibular premolar and molar teeth, thereby describing the relative importance of clinically relevant methods for stress reduction. Conclusions: Vertical loading of an implant-supported prosthesis produced the lowest stress to the supporting bone. Changes in the angle of force application resulted in greater stress to supporting bone. Reduction in prosthesis height or use of an offset implant location for the middle implant reduced stress, but the reduction did not compensate for the increase found with off-axis loading.