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|Title:||下顎骨邊緣切除手術後之骨折預防功效 - 有限元素分析|
Effect of Fracture Prevention after Marginal Mandibulectomy Based on a Finite Element Analysis
|Advisor:||王東美(Tong-Mei Wang),林立德(Li-Deh Lin)|
marginal mandibulectomy,fracture prevention,finite element analysis,defect location,defect extent,residual bone height,
|Publication Year :||2016|
|Abstract:||臨床上，下顎骨邊緣切除術與部分切除術一直是以10mm的殘餘骨高為分界，但此分界點僅立基於一個體外的乾下顎骨實驗。施行邊緣切除術後的下顎骨若以金屬板加強，通常使用由切除區前到後連續的鈦金屬板，但鈦金屬板的彎折費力且費時、客製化又昂貴。本研究之目的在以三維有限元素模型分析下顎骨邊緣切除術的切除區位置、範圍、與殘餘骨高度對術後下顎骨應力分佈的影響，並且探討以連續或不連續金屬板對術後下顎骨加強以防止骨折的效果。本實驗將電腦斷層掃描影像輸入ABAQUS 6.13-2建立下顎骨模型，在模型上切割出由三種不同位置（前牙區、小臼齒區、大臼齒區）、兩種範圍（寬度為34mm或48mm）、與五種殘餘下顎骨高（15.0mm、12.5mm、10.0mm、7.5mm、5.0mm）組合而成的30種切除區，並且在其中一種切除區（大臼齒區、範圍為前後寬48mm、殘餘骨高為5.0mm）裝設連續或不連續金屬板與螺絲。將下顎骨模型的海綿骨與螺絲以十節點之四面體元素、皮質骨與金屬板以三節點之三角形殼元素網格化之後，以ABAQUS 6.13-2求解。研究分為三個部分：第一部分將最大開口及下顎前突時第一小臼齒位置的下顎骨彎曲量與文獻做比較，以探討此下顎骨模型及材料特性、邊界條件、荷載等參數設定之合理性。第二部分為分析不同切除區在門牙咬合及右側大臼齒咬合時最大拉應變與最大壓應變的位置及數值大小，並分別以3000 με與4000 με的應變門檻探討其骨折風險。第三部分為分析裝設連續或不連續金屬板與螺絲的術後下顎骨在右側大臼齒咬合時最大拉應變與最大壓應變的位置及數值大小，並分別以3000 με與4000 με的應變門檻探討其預防下顎骨骨折的效果。
結果：1. 在最大開口及下顎前突時，兩側下顎骨體上緣互相靠近，越往髁頭處靠近的量越多；下緣則是在前面先擴張，往後再逐漸靠近。第一小臼齒位置的下顎骨彎曲量為6.3μm，與文獻數值比較結果在合理的範圍，確認此有限元素模型之設定合理。2. 切除區在右側大臼齒咬合時比門牙咬合時有較高的最大拉應變及較低的最大壓應變。切除範圍越大或殘餘骨高越少則應變值越大。綜合兩種咬合動作之最大拉應變與最大壓應變的結果，要避免骨微損傷出現而開始有骨折風險，無論範圍大小，前牙切除區均需要有12.5mm以上的殘餘下顎骨高度，而小臼齒及大臼齒切除區則均需要有15.0mm以上的殘餘下顎骨高度。3. 裝設金屬板可以將切除區的最大拉應變及最大壓應變值均降低，金屬板越厚，應變值降低的量越多。裝設任一種形式的金屬板後，最大壓應變值均降低到4000 με以下。裝設不連續金屬板比起連續金屬板可使最大拉應變值降低更多，但即使將不連續金屬板的厚度增加到3mm，仍無法使最大拉應變值降低到3000 με以下。
Clinically, surgeons follow a rule of 10 mm to decide whether to perform marginal mandibulectomy or segmental mandibulectomy. However, this rule was based on an experiment performed on a dry mandible with two condyle heads fixed in the cement. Traditionally, reconstruction plates of mandible were bridging two ends of the defect area to reinforce the resected mandible. To manually bend a ready-made reconstruction plate to make it fit the contour of the resected mandible takes time and efforts, whereas to order a custom-made reconstruction plate is expensive. The aim of this study was using three-dimensional finite element analysis to investigate the effect of defect location, defect extent and residual bone height on the stress distribution in resected mandible stress distribution and to investigate the effect of fracture prevention of the continuous reconstruction plate and the separate mini-plates. A basic solid model of mandible was built from CT image and imported into ABAQUS 6.13-2 software. The basic model was transformed into different test models which were designed according to (1) defect location (anterior, left premolar region and left molar region), (2) defect extent (34 mm and 48 mm), and (3) residual bone height (5.0, 7.5, 10.0, 12.5, and 15.0 mm). A continuous reconstruction plate or two separate mini-plates were fixed to one of the resected mandibles (molar defect with 48 mm extent and 5 mm residual bone height) with eight screws. In the mandible model, cancellous bone part and screw parts were meshed with ten-node tetrahedral elements, and cortical bone part and plate parts were meshed with three-node triangular shell elements. The solutions were performed by ABAQUS 6.13-2 software. The study includes three parts. Part I. The finite element model was verified by comparing the volume of mandibular flexure between bilateral first premolars with data in the literature when the mandible was under the conditions of maximum mouth opening and protrusion. Part II. The maximum tensile strain and compressive strain were evaluated in different defect patterns when the mandible was under the conditions of incisor biting and right molar biting. Thresholds of 3000 με and 4000 με for tension and compression sites respectively were used to evaluate the fracture risk of the resected mandibles. Part III. The maximum tensile strain and compressive strain of the molar defect with extent of 48 mm and residual bone height of 5 mm reinforced with a continuous reconstruction plate or two separate mini-plates was evaluated. Thresholds of 3000 με and 4000 με for tension and compression sites respectively were used to evaluate the effect of fracture prevention.
Results: (1) When the mandible was under the conditions of maximum mouth opening and protrusion, the upper border of the bilateral mandibular bodies came close to each other. The amount of closure was the largest between two condyle heads. While observing the lower border, the bilateral mandibular bodies became far from each other at the anterior region and close to each other at the posterior region. The amount of closure due to mandibular flexure over bilateral first premolars was 6.3 μm. The data coincided to the literature. (2) The maximum tensile strain was higher but the maximum compressive strain was lower during right molar biting than incisal biting. The wider the defect extent or the less the remained bone height, the higher the strain. To prevent microdamages and reduce the risk of fracture, the maximum tensile strain and the maximum compressive strain of both biting conditions should be considered. The suggested residual bone height was 12.5 mm for anterior region and 15.0 mm for premolar and molar regions at least to prevent microfracture, regardless of the defect extent. (3) Resected mandibles reinforced with plates showed lower value of maximum tensile strain and maximum compressive strain. The thicker the plates were designed, the more the strain value decreased. The maximum compressive strain was decreased to less than 4000 με with either type of the plate reinforcement. The maximum tensile strain was lower when the mandible was reinforced with two separate mini-plates than with a continuous reconstruction plate. However, even if the resected mandible was reinforced with 3 mm-thick separate mini-plates, the maximum tensile strain was higher than 3000 με persistently.
The study suggested that the fracture risk of mandible with marginal mandibulectomy was related to the defect location, defect extent and residual bone height. And even if reinforced with plates lower the strain of mandible with marginal mandibulectomy, fracture cannot be effectively prevented.
|Appears in Collections:||臨床牙醫學研究所|
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