臺灣博碩士論文加值系統

　　頦帽長久以來，被廣泛應用在生長發育期下顎前突病症的治療。對於其治療效果的評估，近20年有許多臨床研究報告認為頦帽對下顎前突的病人有骨性矯正（orthopedic）的療效；此療效可分為(1)引導（redirection）下顎骨生長方向，(2)抑制下顎骨的生長，(3)促進下顎骨的骨組織重塑（bone remodelling）。
　　本研究目的是以二度空間有限元素測顱X光片分析法（2-D finite element method）探討安格氏三級不正咬合（Angle Class Ⅲ malocclusion）生長期的女生在經頦帽治療後，下顎骨形態的變化。採用有限元素分析法分析主要在於以下特點(1)不需參考平面或參考點；即前後兩坐標平面改變，不影響其分析結果(2)所描述的變化是元素內所有點的變化而非線段長度或角度(3)可探討曲面（curvlinear）形態的變化而不再是傳統分析法所分析的直線變化。實驗選取25位生長期女生，年齡分佈在6~12歲間，其同病徵為有前牙反咬和後牙安格氏三級不正咬合，平均治療時間約1.8年，治療前後各拍攝側面頭顱X光片。為了有限元素法分析在下顎骨選取18個點（datum points），並依此18個點畫分下顎骨為18個有限元素，此劃分法是由幾組不同分法中選取出來，較符合常態反應的模式。進而分析此18個元素在治療前後大小及形狀的改變。而對照組則是選取年齡相似，共同病徵的18組X光片來與治療組作比較。所得結果如下：
　　(1)下顎骨體長（mandible body lengty）和下顎枝長（ramus length）在治療組有顯著生長抑制現象。
　　(2)FEM分析結果中，
　　大小變量（size ration）方面－
　　位於下顎骨體（mandible body）下緣的兩元素KLM和LMR於治療組，size ratio有增大情形（p<0.05）。以整體解剖結構來看，下顎骨體的大小在治療組有減小的情形（p<0.05）。
　　而形狀變量（form ratio）方面
　　元素ABC, CDE, EJK, GMN, KML, LMR, OQR, OMR於治療組，有顯著變化。若以整體解剖構造來看，頦部（chin）的形狀在治療組有顯著變化（p<0.01）。
　　(3)青春期前後分組所得結果，有顯著不同
　　本研究結果和模擬下顎骨受力所得應力（stress）分佈情形，有相當的關聯性；即下顎骨受外力於施力點到整個力量分佈路徑的骨組織會有形態和大小的變化。證實應力的確是骨組織重塑的來源之一。至於應力如何活化造骨細胞和破骨細胞，導至骨吸收及沈積，真正的機轉，需要進一步的研究。

　　Chin cup therapy has been commonly used and widely recognized as a method for correcting malocclusion in the growing prognatic mandible. For the last 20 years, a number of clinical and experimental studies have reported that Chin cup force has several orthopedic effects: (1)redirection of mandible growth; (2)retardation of mandible growth; (3)remodelling of mandible morphology.
　　The purpose of this study was to investigate the bone morphology change or bone remodelling process in ClassⅢ malocclusion subsequent to Chin cup therapy with finite element method analysis. The finite element method analysis has several characters that can overcome some conceptual and technical constraints of customary roentgenographic cephalometric methods. FEM provide invariant descriptions of growth kinematics that are independent of their underlying, causally related, dynamics. Since FEM utilized the principles of continnum mechanics, it (i) describes the kinematics of nodal point growth behavior of any given element mesh and, (ii) provide a field result with interpolation techniques which can not be accomplished with traditiomal approach. The two attributes above suggest that FEM provides quantitative descriptions of both the functional metrices and the skeletal units enclosed within the boundaries of a given finite element mesh.
　　The subjects in this study consisted of 25 growing girls who showed anterior crossbite and Angle Class Ⅲ malocclusion before treatment. All underwent chin cup therapy from, the beginning of treatment. The duration of chin cup therapy varied but average 1.8 years. Eighteen cephalometric points on the mandible were digitized on preteatment and posttreatment lateral cephalograms of patients whose age ranged between 6 to 12 years old. By using 18 of these digitized points, the mandible were discretized into 18 triangular finite elements representing different areas of mandible. Four parameters were used to describe changes of finite elements and compare to the control groups of 18 cases without chin cup treatment.
　　The results were described as:
　　(1)The cephalometric parameters for changes in absolute mandibular length are given by mandibular ramus length and mandibular body length. Both of these values showed decrease in percentage value from the control rate of change during active therapy.
　　(2)In the FEM results, there are two elements of treatment groups on the lower border of mandible, KLM and LMR, showed increase in size ratio (p<0.05). And from the anatomic view, the mandibular body showed decrease in size ratio of treatment groups.
　　(3)In the FEM results, there are several elements of treatment groups,including ABC, CDE, EJK, GMN, ELM, LMR, OQR, OMR elements, showed significant change in form ratio. And from the anatomic view, the chin area showed significant change in form ratio of treatment groups.
　　(4)Pre end post-adolescent period can lead to FEM results different.
　　From these results on comparing the control and therapeutic changes of the mandible, it may be assumed that orthopaedic chin cup force modify normal mandibular growth and closely associate with mandibular remodelling. However, details of the mechanism about the cellular activity inducing bone resorption and deposition are still unclear and hence further investigartion with biomechanical, histological approaches will be needed in future studies.