Influence of implant shape and placement design to stress distribution

Objectives: Finite element analysis was conducted to determine the magnitude of stress in the supporting bone when parallel sided (cylinder) or tapered implants are used to support prostheses while changing implant offset, and angle of force. Materials and Methods: Two 3-D FEA model of the mandible were created using PATRAN software .Three titanium implants (3.75 mm diameter -10 mm in lengths parallel side, and 3.75 mm diameter -10 mm in lengths tapered) were placed into each model at a distance of 7 mm center to center. The center implant was placed on the line from the centers of the terminal implants, 1.5 mm lateral to this line or 3.0 mm lateral to this line. An implant-supported prosthesis was simulated in the height of 12 mm. 200 N forces were applied in a straight vertical direction or in 15 degree increments to the vertical (15, 30, 45 and 60 degrees). Stress in supporting bone was analyzed using ABAQUS software. Results: The lowest stresses in the supporting bone were found with vertical loading, no offset 3.86 MPa for parallel, and 9.62 MPa for tapered. Changing the angle of force application by 15 degree resulted in increased stress to the underlying bone 16.91 and 29.6 MPa respectively. Creation of 3 mm offset compensated for this increased stress (9.24 and 17.5 MPa). Conclusion: The lowest stress around the supporting bone was measured when the vertical load applied. Changing in angle of force application from vertical causes an increase in stress. A 15 degree change in the angle of force further results in greater stress to supporting bone. An offset implant location reduces stress for both implant designs. Parallel sided implants demonstrate less stress concentration within the supporting bone than tapered (root form) implants.