牙周韌帶厚度模擬對下顎小臼齒有限元素模型應力影響之探討

The Effects of PDL Simulations for a Mandibular Premolar FEM Model

雷曜寧(Yao-Ning Lei)

指導教授 ： 王兆祥

高雄醫學大學/口腔醫學院/牙醫學研究所/碩士(2005年)

摘要

牙周韌帶的模擬在利用電腦輔助分析來探討牙科生物力學行為的研究中一直是受到爭議的環節，牙周韌帶在電腦輔助分析模型中對於擬真目標的達成相當重要的，卻鮮少有人充分討論。目前許多生物體組織的力學行為以及材料性質的範圍和變異性都很大，使得有限元素分析的結果無法獲得確定的認同。本研究利用電腦輔助分析，探討不同的牙周韌帶模型，在不同方向的受力情況下對於下顎第一小臼齒應力分布的影響，希望模擬出可信度、接受度高的模型，以獲取各種模擬設計所帶來的差異作為相關實驗之參考。本研究利用切片掃描建構下顎第一小臼齒的有限元素模型，在以輸入方式建立牙根周圍分別為 0 mm、0.25 mm、0.5 mm、0.75 mm以及不均勻厚度為2:1:3 ( 0.5 mm 、0.25 mm、0.75 mm )的生理性比例牙周韌帶模型，再分別施予垂直及水平施力170N。經由有限元素應用軟體ANSYS (ANSYS 5.6, ANSYS Inc in order. USA) 運算之後，繪製出各種應力分布圖。結果發現，加入牙周韌帶的模型其應力分布情形較相似，而與不使用牙周韌帶模型的結果有差異；牙周韌帶能夠吸收並引導應力，減少齒槽骨與牙齒內部結構的應力集中，趨勢會隨著韌帶厚度增加而明顯；牙周韌帶能將牙冠所受外力透過更大範圍牙根傳導，因此改變模型上牙齒及牙周組織的應力分布，生理性比例厚度比均勻厚度的牙周韌帶會產生較合理的應力分布狀況，但同時牙周韌帶的模擬也可能會造成不同區域應力分布的錯估。因此牙周韌帶的加入對於應力分布分析的結果是有影響的，但由實驗中無法得知應力分布結果是否更趨近於真實狀況。牙周韌帶的取捨應依照實驗目的以及韌帶所可能造成的影響來做評估。

關鍵字

有限元素分析 ； 牙周韌帶模擬 ； 生理性牙周韌帶

並列摘要

In times, the numerical techniques of the finite element method (FEM) are more and more destined to simulate stress distribution induced by occlusal force systems. Unfortunately, there are still not definitive principles for model construction of periodontal ligament by finite element method. This study, adopting a standardized model, undertook finite element analysis to explore the stress distribution situation when a single lower first premolar with various periodontal ligament thicknesses was putted under occlusal force; the results can be applied for further FEA models and a clinical reference. A lower first premolar of standard model was embedded in the transparent resin and cut into thin slices. The slices were scanned onto the computer to obtain an image of accurate dimension and outline. The outline was then subdivided into new geometrical key points. Entering the theses key points into CAE software (ANSYS 5.6, ANSYS Inc in order. USA) produced sets of significant data including lines, surfaces and volumes, thus ultimately created a solid model. The whole model was presumed to be an isotropic and homogeneous material with various thicknesses. The models simulated the periodontal ligament thickness of approximately 0 mm, 0.25 mm, 0.5 mm, and 0.75 mm. Another model is also constructed to simulate the PDL of physically uneven thickness with a proportion of 2:1:3 ( 0.5 mm at cervical third, 0.25 mm at middle third and 0.75 mm at apical third of the root ). It was then placed in a cubic block simulating a tooth in a schematic alveolar bone surrounding. Vertical and horizontal forces of 170 N were separately applied on the tooth. The stress distributions on root, bone and periodontal ligament were then observed. The results for the PDL of various thicknesses are more similar to each other than to those without any PDL. The PDL plays a role of stress distributor, redirecting the stress throughout the whole tooth i.e. crown to root and the surrounding tissue. It also decreases the stress on crestal bone. The model with proportionally varied thickness reveals more reasonable distribution pattern than that with even thickness. But it can’t be confirmed if the simulated stress distributions approach the actual situation by the result. The necessary data about periodontal ligament orientations, distributions, mechanical properties, and how they change during loading and function, are not available. It may be more prudent to add nothing into the FEA model than to include an imprecisely simulated one.

並列關鍵字

periodontal ligament simulation ； finite element analysis ； physically proportioned Periodontal ligament

參考文獻

參考文獻

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