| Summary: | 碩士 === 臺北醫學大學 === 牙醫學系碩博士班 === 97 === Clinical findings indicated that the geometrical shape of the mandible was deformed during mouth opening. This deformation results in a reduction in the width of the mandibular arch. According to the rigid connection of dental implant and bone tissue, some authors indicated that edentulous mandible treated with implants supported fixed partial denture and connected by a one piece cross-arch superstructure could generate dangerous stresses both at bone-implant interface and prostheses superstructure, and high stress concentration might lead to failure of the osseointegration and the fracture or loosening of the prostheses.
In this study, a finite element method was used to evaluate the effect of different types of implant supported fixed partial dentures on the mandibular deformation. The mandible model with natural dentition and five mandible models with implants and prostheses were developed. Five mandible models treated with : only eight implants and eight implants connected by one, two, three and four-piece superstructures. Additionally, the same forces and orientations of masticatory muscles were considered to simulate opening movement in this study. Then, the stress distribution of the prostheses and implants in different designs of implant-supported prostheses were analyzed for discussion.
Our results demonstrated that the mandible models with natural dentition and implants presented a decrease in mandibular arch during opening. The changes in width between the mandibular molar area in the mandible model with natural dentition and the mandible model treated with eight implants but not connected by superstructure were 0.212 mm and 0.249 mm, and the dimensional changes were decreased from the posterior to the anterior area, and these results conform to the clinical studies. We also found that, stress concentrated at the symphyseal area of superstructure during opening movement, and separating the superstructure at the symphyseal area will decrease the stress concentration of implant prostheses. In comparison with one-piece cross arch superstructure, two, three and four sections of the superstructure will decrease the stress of implant prostheses. During opening movement, stresses were concentrated at the implant-bone interface close to the implant neck. Especially the most distal implant in the mandible model treated with a one- piece cross arch superstructure, and implants connected with four-unit superstructure present stress concentration more equally.
The results indicated that the mandibular deformation and the stress concentration on implant-bone surface and prostheses are related to the different superstructure designs of implant supported fixed partial dentures. Therefore, we suggest that, the dentists should pay more attention to prostheses design on implant supported prostheses in edentulous mandible.
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