| Summary: | 博士 === 國立臺灣科技大學 === 機械工程系 === 97 === The purpose of this study was to compare the effects of various designs of implants’ placement on stress distribution in bone around the implants supporting one-unit fixed prosthesis. A computer tomography image was redrawn to reconstruct a digital three-dimensional solid model of a mandible including the cortical bone and cancellous bone. Moreover, the reverse engineering method and computer-aided design were employed to construct fourteen pieces of digital three-dimensional solid model of teeth including the anterior and posterior regions as well as implant and abutment. Each tooth was cut along the cervical line to obtain the crown, and all of the crowns were connected by using the MSC/PATRAN software and called the fixed prosthesis. All of the digital three-dimensional solid models were combined and transformed to the FE models by using the MSC/PATRAN software, and they were classified into 27 configurations according to the number and location of the implants. The MSC/PATRAN software was used to develop the FE mesh of each model comprising of 1,101,954 elements with 252,693 nodes. The MSC/NASTRAN software was utilized as pre and post-processor for all mathematical calculations necessary to evaluate dental and mandibular biomechanics. One set of multiple vertical loads was used to simulate the possibility of occlusion status. And the von Mises stress values in the cortical bone, cancellous bone and implants were evaluated. The simulated results indicated that the stress distributions for FE models were largely affected by the number and location of implants. In the bone, similar to the single-tooth case, the von Mises stresses were all concentrated toward the cortical bone around the collar of the implants for FE models. In the 4-implants system, the model F-8 was generated the lowest MVMS in the position L6 of the cortical bone; in the 6-implants system, the model S-6 was generated the lowest MVMS in the position L5 of the cortical bone; in the 8-implants system, the model E-3 was generated the lowest MVMS in the position L5 of the cortical bone; in the 10-implants system, the model T-3 was generated the lowest MVMS in the position L5 of the cortical bone; in the 12-implants system, all of models were generated lower VMS in the cortical bone ; in the 14-implants system, the model FT-1 was generated the lowest MVMS in the position R6 of the cortical bone. From the literatures, the ultimate strength in the cortical bone surrounding the cervical regions of implants and the implant were about 100 and 550 MPa, respectively. If the loadings were increased to 5 times in this study, the MVMS of all materials would be increased to 5 times, too. According to these conditions, the model of F-8, S-6, E-3, T-3, TW-3 and FT-1 would be the best designs for each implant system and suitable to use in the clinical surgery. From the above statements, with more supporting implants, the treatment may be safer.
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