Evaluation of the Effect of Cortical Bone Thickness on Stress Distribution in Implant-Supported Fixed Prostheses

Abstract

PurposeThe purpose of this study was to evaluate and compare the effects of fixed prostheses placed on mandibles with different cortical bone thicknesses, achieved through different treatment plans, on the stress levels of the prosthesis substructures, surrounding and supporting bone tissues, and implants under masticatory forces using finite element analysis (FEA).MethodsFour different implant-supported prosthesis models were designed (M1 = all-on-four, M2 = 4 vertical implants in parallel and straight configuration, M3 = trefoil, M4 = all-on-three). For each treatment plan, the cortical bone surrounding the implants was modeled with four different thicknesses. In all models, chewing forces (100 N total, 25 N per region) were applied bilaterally in the mandibular canine and second premolar regions using the foodstuff method. Von Mises stresses on the prosthesis bars and implants, as well as the minimum and maximum principal stresses in the surrounding bone, were compared using FEA.ResultsThe highest stress values were observed in the M4 plan, where the cortical bone was modeled with a thickness of 0.5 mm (maximum stress value, for supporting bone: 5438 MPa; for implants: 22,783 MPa; for infrastructure material: 14,524 MPa).Increasing the cortical bone thickness in all treatment plans resulted in a decrease in stress values on the prostheses and supporting bone. When the treatment plans were evaluated based on stress values, the ranking from lowest to highest stress values was as follows M4 = all-on-three, M3 = trefoil system, M2 = 4 implants, and M1 = all-on-four system. (Minimum stress value, for supporting bone: - 0.085 MPa; for implants 3622 MPa; for infrastructure material: 5205 Mpa.ConclusionCortical bone thickness is a crucial factor in preventing damaging stresses in the supporting tissues during the planning of implant-supported fixed prosthesis. The evaluation of cortical thicknesses in mandibular resorbed cases obtained comparable results to other protocols in both alfalfa and three-in-one systems. Nevertheless, the treatment plan with four implant support proved to be the most beneficial for tissue stress values. Further clinical studies are necessary on this subject within the constraints of FEA analysis.