下顎第一大臼齒近心牙根切除後之應力分析
-有限元素法

中文摘要前言：大臼齒由於其所處牙弓位置與解剖型態之關係，是口腔中最易發生牙周病之牙齒。牙根切除術為治療根叉病變方式之一，而牙根切除術治療長期追蹤之結果，成功率約6成。失敗的原因不外乎蛀牙、牙周破壞、根管治療失敗及牙根斷裂，其中除了根管治療失敗的原因之外，其餘失敗的原因均與應力的發生有關。目的：利用電腦輔助分析配合電阻應變實驗驗證的方式，在不同齒槽骨高度，以及不同方向受力負荷狀況下，對根叉受侵犯齒在接受近心牙根切除術並製作其遠心根與第二小臼齒相連之固定補綴物後，比較切除前後牙齒與齒槽骨應力分佈之情形。材料與方法：模擬下顎第一大臼齒及第二小臼齒在牙釉牙骨質交界下 2 mm之齒槽骨高度為樣本，樣本經由鑽針修磨、牙髓組織樹脂複製及雷射掃描後，經影像處理建成三維有限元素模型，並由電阻應變實驗分析印證其有效性之後，利用電腦軟體處理將第一大臼齒近心牙根切除，並模擬其遠心根與第二小臼齒相連之固定補綴物設計，進行有限元素分析，施力設於固定補綴物頰側咬頭(此位置相當於切除前大臼齒近心頰側咬頭、頰側咬頭、第二小臼齒頰側咬頭)，方向計有垂直咬合平面(P1)、頰側45°(P2)、舌側45°(P3)三個不同施力方向。本研究針對四種不同齒槽骨高度設計形式(分別為CEJ下4、5、6、7 mm)在三種方向咬合力下對根叉受侵犯齒在牙根切除合併補綴復形後，牙齒與齒槽骨之應力分佈情形來加以探討。結果：下顎第一大臼齒近心牙根切除術後，牙齒應力(σvon Mises、σmax與σmax shear)集中處為牙齒頰舌側表面與第一大臼齒近心側牙髓腔開口下緣。牙齒應力(σvon Mises、σmax與σmax shear)於CEJ下7mm骨頭高度時為最大。在P3施力方向下，於牙齒應力(σvon Mises、σmax與σmax shear)為最大。齒槽骨應力(σmin)集中處為第一大臼齒之齒槽嵴。齒槽骨應力(σmin)於CEJ下4mm骨頭高度時為最大。在P3施力方向下，於齒槽骨應力(σmin)為最大。牙齒與齒槽骨的應力在牙根切除術後較牙根切除術前高。結論:牙根切除後第一大臼齒近心側牙冠邊緣上方與牙髓腔開口之間為應力集中處，隨齒槽骨下降，應力有增加之趨勢。此外，齒槽嵴為齒槽骨應力集中處，應力並未隨齒槽骨下降而上升。側方施力會在牙齒與齒槽骨產生較大的應力，尤其舌側施力。牙根切除術後牙齒與齒槽骨應力均有增加的情形。

關鍵字

根叉受侵犯；牙根切除術；有限元素分析；應力分析

並列摘要

英文摘要 Introduction: Periodontal disease occurs mostly in molar area because of the position of the molar region and the complexity of the anatomical form. Root resection is one of the treatments, when the furcation of molar teeth is involved in periodontal disease. As long-term trace of root resection-treatment has shown, the success rate is about 60%. Main causes for failure include caries, periodontal disease, endodontic origin, and root fracture. Except endodontic origin, the other causes are all related to biomechanical stress. Purpose: The objective of this study is to, firstly, analyze the stress of furcation-involved molars with mesial root resection; secondly, fixed prosthetic reconstruction at different alveolar bone heights with various loads by CAD/CAE; and finally, experiment on strain measurement for validity treatment. The stress after root resection is to be compared with that before resection. Material and method: The sample is simulated to the mandibular first molar and second premolar when the alveolar bone height is below 2mm of CEJ. The three-dimensional models of finite element are constructed through mimicries of tooth preparation, resin casting of pulp tissue, and laser scanning. Following the test of effectiveness based on strain gauge technique, molar models after mesial root resection and fixed prosthesis reconstruction are formulated through computer software. Finite element analysis is also utilized to study the model. Force is applied to the fixed prosthesis buccal cusps–location as mesiobuccal cusp and buccal cusp of first molar and buccal cusp of second premolar before resection—from three different directions: directly perpendicular to the occlusal plane (P1), buccal 45˚ (P2), and linual 45˚ (P3). From the four alveolar bone height designs (below CEJ 4, 5, 6, 7mm) under three directions of occulusal loadings, this study analyzes the stress distribution of tooth and alveolar bone when furcaiton-involved first molar with mesial root resection and fixed prosthesis reconstruction. Result: After mesial root-resection of lower first molar, the von Mises stress, maximal principal stress, and maximal shear stress concentrate on the teeth around the buccal and lingual surfaces and the lower margin of the pulpal chamber of first molar mesial surface. Stresses maximize either when the alveolar bone height is below CEJ 7mm or with P3 loading direction. Minimal principal stress in bone concentrates around alveolar crest. Stress maximizes either when the alveolar bone height is below CEJ 4mm or with P3 loading direction. In comparison with an untreated molar, an increase in stress on a furcaiton-involved molar with hemisection and fixed prosthetic reconstruction become more observable. Conclusion: Stress on the teeth concentrate on the lower margin of the pulpal chamber of the first molar mesial surface, and it will increase with the reduction of bone level. Stress on the bone concentrate on alveolar crest, but it does not increase according to the reduction of bone level. Both stresses go higher when lateral forces are applied, especially from the lingual direction. Root resection increase and redistribute the stress on the bone and abutment teeth.

並列關鍵字

Furcation-involved ； Root Resection ； Finite Element Analysis ； Stress Analysis

參考文獻

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