臺灣博碩士論文加值系統

牙科植體在無牙患者贗復治療上是一項大的進步。但是不當的應力(stress)會導致骨吸收，破壞骨結構的完整性，造成植體的失敗。因此，值體周圍骨組織結構的維持是骨整合式(osseointegrated)骨內植體長久成功最重要的因素。以往曾經利用有限元素法評估植體周圍的骨應力，但多未能將臨床上的情形加以考慮。因此，吾人考慮到臨床上的情況，利用有限元素法(finiteelement method)建立實際可能遇到的多種骨質與負荷情況的軸對稱有限元素模型(axisymmetric finite element model)。本研究的目的在檢視不同的植體形狀與骨質對植體周圍骨應力分佈的影響。吾人比較七種市面上不同形狀的體植：Bicortical-Schraube,Branemark, Screw-Vent, Steri-Oss, Minimatic, Pitt-Easy,Micro-Vent，及兩種自行設計的植體：A1,B1。模擬臨床上可能遇到的四種骨質情況：分別為均質皮質骨，均質鬆質骨，單層皮質骨及雙層皮質骨。此外，藉著改變負荷的方向：100牛頓的垂直負荷及30度之斜向負荷分別施於植體的頂端，以觀察多種骨應力的分佈型態。分析結果顯示：不同的植體形狀，不同的負荷情況及不一樣的顎骨骨質都會影響骨應力的分佈。外形不連續的植體表面(如螺溝，橫溝槽及尖銳處)會導致較高的骨應力。然而，長柱狀的植體冠部比短柱狀的冠部在斜向負荷時會產生更高應力。斜向負荷產生之最大骨應力值比垂直負荷者大甚多，且集中於冠部之少骨質。分析亦顯示：皮質骨有較均勻的應力分佈，在應力傳導方面優於鬆質骨。而雙層皮骨的結構是為一良好且值得建議的植牙區選擇。無論如何，分析的結果要花臨床上應用，仍須要再結合對骨結構之生物及臨床的研究。

Utilizaton of dental implants in restoration of edentulous patients is the progress of dental science. Stress can induce resorption in the surrounding bone of implants, leading to gradual loosening and ultimately to complete loss of implants. Thus, the maintenance of periimplant bone structure plays an important role for long term success of osseointegrated implants. Previous study has used the finite element method to assess mechanical stresses occurring in bone surrounding dental implants. However, little has been done to related the calculated stress distributions to clinical situation. In this investigation, to avoid the limitations stated, we made axisymmetric finite element models of various bone qualities and loading directions to simulate clinical conditions. The aim of this investigation is to evaluate the effects of different implant shapes and bone qualities on stress distribution in bone. Nine different root-type endosseous implants are included in this study. Among them are seven commercial cortical-Schraube, Branemark, Screw-Vent, Steri-Oss, Minimatic, Pitt-Easy, and MicroVent), two self-designed implants (A1, and B1). Four types of bone are modeled for this study: homogenous cortical bone, homogenous cancellous bone, a cortical bone layer superior to cancellous bone, a cortical bone layer superior to cancellous bone and the other inferior. 100-newton loadings of an axial direction and a 30-degree oblique direction to the axis are applied over the top surface of each implant. The results indicate that the stress distribution pattern is determined by implant shape, bone quality, and loading condition. Implant surfaces with geometric discontinuities (serrated, grooved, and sharp geometries) lead to high-stress concentrations at the tips of the bony ingrowth. Moreover, a smooth, longer cylinder shape of implant head causes higher stresses than shorter shape under oblique loading. Oblique loading produces more greater maximun bone stress than vertical, and concentrated in the little volume of crestal bone. In this study, the cortical bone will be advantageous for the stress delivered to bone, since it produces a more uniform stress distribution than does cancellous bone. it suggests that bone model of a cortical bone layer superior to cancellous bone and the other inferior is a good selection for operation site of implant. However, additional researches, combining biological and clinical studies, were recommended for all commercially available dental implants.