最大開口時下顎骨變形量之量測及其影響因素之探討

背景：臨床上當固定式義齒的連結跨越下顎骨兩側而延伸至後牙時，在下顎前牙接近頦骨聯合處(symphysis)經常可以發現義齒陶瓷破裂或是黏著劑失敗(wash out)的情形。對於這些原因不明的失敗，推測可能是由於下顎骨在做咀嚼、張口或前凸運動的時候，因肌肉的牽扯而產生下顎骨變形所致。然而目前文獻卻大多著重於討論下顎骨變形量的多寡，鮮少針對可能影響下顎骨變形量的相關因子進行探討。研究目的：本研究希望藉由觀察並探討這些可能因素，了解影響下顎骨變形的相關條件，以提供臨床治療參考。研究方法：實驗選取72位自願參與研究者。首先，使用特製不銹鋼之印模咬叉以及自動混合調拌矽膠印模材(automatically mixed vinyl polysiloxane material; O-bite, DMG, Hamburg, Germany)，取得受測者最小張口及最大張口時下顎雙側第一大臼齒的位置紀錄，並量測其寬度變化。同時每個受測者拍攝錐狀射束電腦斷層影像 (imaging science i-Cat; NewTom VGi ) 取得可能相關因素，如：下顎骨長度、頦骨聯合寬度和高度、頦骨聯合皮質骨厚度、兩側髁頭的夾角、兩側外翼肌夾角和肌肉寬度的資料。而後將所得資料進行相關統計分析。結果：實驗測得下顎骨最大張口時變形量平均為0.17 ± 0.09 mm，其中最小為0.01 mm，最大為0.40 mm，男女並無明顯差異。經由統計分析得到，兩側髁頭夾角對下顎變形量之影響在統計上具有明顯意義(β=0.0024, p=0.03)。結論：本實驗結果驗證下顎骨在最大張口時確實有變形的情況產生，但個人差異性很大。其中兩側髁頭夾角對下顎變形量之影響在統計上有明顯意義，並呈正相關，意即兩側髁頭夾角越大，則下顎張口變形量也會越大。

關鍵字

下顎形變；頦骨聯合；髁頭夾角

並列摘要

Background: Elastic deformation happens during forced movements of the mandible and it may affect the clinical success of extensive bilateral prostheses in the mandible. Objective: The purposes of this study are to investigate the mandibular deformation of maximum mouth opening, and to search for affected factors. Materials and Methods: Seventy two dental students volunteered for this study. Eligibility criteria included complete mandibular dentition (facultative presence of third molars) and subjects were excluded if they had a history of maxillofacial surgery, mandibular trauma, or orthodontic treatment within the previous two years; for presence of active periodontal disease with tooth mobility, bruxism, osseous or neuromuscular diseases. Bite registrations at mandibular both contralateral first molar were recorded when maximum and minimum mouth opening. Proposed factors such as mandibular length, symphyseal width and height, the angle of condyle head, the direction and width of lateral pterygoid muscle were measured by using conebeam CT. After the data were collected, they were analyzed with two sample t-test and regression analyses to evaluate the influence of the affected factors. Results: The results show that the mean value of the changes in width between the mandibular first molars of the total sample was 0.17 ± 0.09 mm, and 0.17 ± 0.09 mm, 0.18 ± 0.08 mm for the male and female individually. The measurements from the deformation of mandible was significantly correlated to the angle of condyle head . Conclusions: The results showed that mandible width narrowed in maximum opening ; and there were wide variations between subjects. The angle of condyle head is closely related to mandibular deformation on mouth opening.