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Effect of Plate Reinforcement on Fracture Prevention after Mandibulectomy: A Numerical Analysis
mandibulectomy,finite element analysis,cutting angle,plate reinforcement,fibular free flap,risk of bone fracture,
|Publication Year :||2019|
|Abstract:||臨床上，邊緣下顎骨切除術與部分下顎骨切除術一直是以10mm的剩餘骨嵴高為分界，但10 mm rule是基於一個體外的乾下顎骨實驗。在邊緣切除術後的下顎骨若要以金屬重建板加強，需要彎折市售的鈦金屬重建板去貼合切除區前後，但鈦金屬重建板的彎折費力且費時、客製化又昂貴，但偶有術後骨折的狀況發生；因此本研究希望利用三維有限元素模型分析下顎骨大範圍邊緣切除術後不同補強設計對術後下顎骨應變分佈的影響：直角切線設計和圓角切線設計、不同設計鈦金屬重建板，以及部分下顎骨切除後用腓骨皮瓣重建後的骨折風險狀況。本實驗將電腦斷層掃描影像輸入ABAQUS 6.14-1建立下顎骨模型，選擇術後所受應變最大的大臼齒區大範圍（48mm）切除區作為實驗對象，在模型上切出四種殘餘下顎骨嵴高（15.0mm、12.5mm、10.0mm、7.5mm）。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 6.14-1求解；研究分為三個部分：
第一部分探討右大臼齒咬合時，左側大臼齒邊緣大範圍切除在不同切線設計時（直角切線設計與圓角切線設計），所受之最大拉應變與最大壓應變的位置及數值大小，並分別以3000 microstrain與4000 microstrain的應變門檻探討其骨折風險。
第二部分承接第一部分，在同樣的切除區及咬合型態，分析用不同設計之鈦金屬重建板固定時，所受之最大拉應變與最大壓應變的位置及數值大小，並分別以3000 microstrain與4000 microstrain的應變門檻探討其骨折風險。
第三部分探討右大臼齒咬合時，左側大臼齒部分下顎骨切除後用不同厚度腓骨皮瓣移植後，下顎骨最大拉應變與最大壓應變的位置及數值大小，並分別以3000 microstrain與4000 microstrain的應變門檻探討其下顎骨骨折的風險。
Compared to segmental mandibulectomy, marginal mandibulectomy keeps the continuity of mandible after tumor resection, and then gets better esthetic and functional outcomes. Clinically, many surgeons follow the “ 10 mm rule” to decide to perform marginal mandibulectomy or segmental mandibulectomy. However, this rule was based on the result of Barttlebort’s in vitro study, performing on a dry mandible with two condyle heads fixed in the cement. Traditionally, reconstruction plates of mandible are bridging two ends of the defect area to reinforce the resected mandible. It takes time and efforts to manually bend a ready-made reconstruction plate to make it fit the contour of the resected mandible, whereas it’s expensive to order a custom-made reconstruction plate. Although the mandibles were bridged with reconstruction plates, there were still some fractures occur after surgery. Therefore, the aim of this study was using numerical analysis to investigate the strain distribution on mandible after extensive marginal mandibulectomy and to investigate the effect of fracture prevention of different cutting angle and different reconstruction plates. And the risk of fracture in segmental mandibulectomy patients repaired with fibular free flap was also investigated.
A basic solid model of mandible was built from CT image and imported into ABAQUS 6.14-1 software. The experimental models were set as left extensive resected area (48mm) under the occlusal scheme of right molar biting. Four groups of residual bone height (7.5, 10.0, 12.5, and 15.0 mm) were investigated. 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 6.14-1 software. The study includes three parts.
Part I. Left extensive marginal resected defect under right molar biting. The cutting line angle with higher tensile strain was designed as right angle or curved. The differences of maximum tensile strain and compressive strain in these two designs were evaluated. Thresholds of 3000 microstrain and 4000 microstrain for tension and compression sites respectively were used to evaluate the fracture risk of the resected mandibles.
Part II. In the same situation as part I, we investigate the reinforcement effects of three types of reconstruction plates: I shape, L shape, and T shape. Thresholds of 3000 microstrain and 4000 microstrain for tension and compression sites respectively were used to evaluate the fracture risk of the resected mandibles.
Part III. The maximum tensile and compressive strain on extensive segmental defect site, which was restored with fibular free flap, was evaluated. Thresholds of 3000 microstrain and 4000 microstrain for tension and compression sites respectively were used to evaluate the effect of fracture prevention.
Results: (1) Comparing to right cutting angle, curved cutting angle can reduce MCS and MTS. While the residual bone height was lesser, the strain became larger on the left extensive defect site during right molar biting. The risk of bone fracture couldn’t be avoided in all groups. (2) Curved cutting angle combined with reconstruction plate reinforcement can decrease MCS and MTS effectively, especially in the thinner residual bone height group. (3) If the residual bone height was limited (less than 15 mm), each plate design performed better than no reinforcement group on MTS and MCS. However, the maximum tensile strain was higher than 3000 microstrain persistently. (4) There is no difference in using two screw fixation or three screw fixation. (5) Segmental mandibulectomy patients restored with fibular free flap still have risk of bone fracture.
The study suggested that after extensive marginal mandibulectomy, the bone fracture risk existed in the residual ridge height less than 15 mm. Curved cutting angle and plate reinforcement is necessary to decrease the strain, but fracture cannot be effectively prevented. The bone fracture risk still existed in segmental mandibulectomy patient repair with fibular free flap.
|Appears in Collections:||臨床牙醫學研究所|
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