and 1 other(s)
Background; Slight offset of the central implant in 3-unit implant-supported prostheses has been recommended to improve biomechanical behavior. However, studies that assessed the effects of an offset implant congfiguration in the posterior mandible are rare. Aim/Hypothesis; The purpose of this 3-dimensional (3D) finite element study was to assess the effects of load direction and number of implant in 3-unit implant-supported prostheses with varying implant positions (straight-line or offset) on the stress distribution in the implant, prosthesis, and bone tissue. Materials and Methods; Three 3D models were used to simulate a posterior mandible bone block: 2 implants and 3-unit fixed dental prosthesis(FDP) with a pontic in the middle (model M1), 2 implants and 3-unit FDP with a cantilever pontic at one end (model M2), FDP supported by 3 implant with straight line placement (model M3) and FDP supported by 3 implant with staggered implant configuration (model M4). The applied forces were 120 N axially (L1), or 120 N obliquely(L2). The type of implant platform simulated was an external hexagon. Maximum von Mises stress (VMS) on the fixture, abutment, screws, fixed prosthesis and supporting alveolar bone was measured and analyzed. Results; Peak VMS in the implants by oblique loading were 10-25 times greater in implant and 6-12 times greater in alveolar bone, respectively than the stresses by axial loading. Compared to the maximum stress value of the implant by oblique loading in model M1, the maximum stress value increased to 116% in M2, but decreased to 74% and 71% in M3 and M4, respectively. In the cantilevered M2 model, the maximum stress values in the FDP were 851.5 and 908.4 MPa, respectively, by the vertical and oblique loadings, which are 5.1 and 7.1 times higher than the other models, respectively. The area of maximum stress in the implant was located around the area where the abutment screw and fixture were connected. Stress concentration was observed at an abutment screw by oblique load and at the top of the implant fixture by axial load. In the supporting bone, the maximum stress value increased to 120% in M2, but decreased to 69% and 63% in M3 and M4, compared to the stress in M1 by oblique load. Conclusions and Clinical Implications; The effect of staggered alignment on implant stress was negligible, but the cantilever design of the prosthesis and the number of implants had a greater impact on stress distrubution.
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