下顎小臼齒裝置牙根柱時其鄰接面不同齒質缺損對應力之影響－有限元素法

Biomechanical analysis of post and core for mandibular first premolar with different proximal decay － finite element method

楊駿彥(Jyun-Yan Yang)

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(2009年)

https://doi.org/10.6832/KMU.2009.00084

摘要

臨床上常見牙齒經根管治療及贗復完成後發生牙根斷裂的情形。回顧文獻得知影響牙齒抗破折強度的關鍵為冠部殘存齒質的多寡。但於牙齒因嚴重鄰接面齲齒造成牙髓炎而需根管治療的情況下，究竟此類患齒是否因局部齒質缺損而影響整體結構強度造成牙根斷裂？然文獻回顧大多討論完整冠部齒質究竟該有多少才恰當，較少針對局部齒質的缺損對強度的影響。因此本研究利用有限元素軟體(ANSYS)分析局部齒質缺損時，裝置牙根柱後之應力變化，以提供臨床治療參考。
本研究以人類下顎第一小臼齒三維實體模型，模擬不同形式齒質缺損，分別為：齒頸部上2 mm齒質完整模型(A)、近心端1 mm齒質缺損模型(A1)、近心端2 mm齒質缺損模型(A2)、近心端2 mm齒質缺損及遠心端1 mm齒質缺損模型(A21)、近心端2 mm齒質缺損及遠心端2 mm齒質缺損模型(A22)、齒頸部上0.5 mm齒質缺損模型(B) 、齒頸部上1 mm齒質缺損模型(C) 、齒頸部上1.5 mm齒質缺損模型(D)及齒頸部上2 mm齒質缺損模型(E)，共九組模型於不同方向作用力時應力變化。負荷條件的設定方面，本實驗在此九組模型分別給予五個方向皆為100 N的施力，分別計算其施力結果。LV：沿著牙齒長軸通過頰側咬頭頂點的垂直力；LB：與牙齒長軸交角45°通過頰側咬頭頂點由頰側往舌側的側方力；LL：與牙齒長軸交角45°通過頰側咬頭頂點由舌側往頰側的側方力；LM：與牙齒長軸交角45°通過頰側咬頭頂點由近心往遠心的側方力；LD：與牙齒長軸交角45°通過頰側咬頭頂點由遠心往近心的側方力。
結果顯示：垂直力作用下，隨著齒質缺損程度提高，對牙根σ von Mises最大值影響不大，對牙根柱應力最大值及應力分布位置有影響；側方力作用下，除齒頸部上1.5 mm及2 mm齒質缺損模型(D及E) 外，於其它七組模型中，對牙齒齒質及牙根柱應力分布的影響並不明顯。實驗結果顯示冠部齒質至少須有1 mm，才能有效減緩側方力的影響；當鄰接面齒質缺損在其冠部齒質其它部位至少有1 mm時，於不影響贗復物製作情況下，不需為了對局部區域要獲得足夠冠部齒質而作特殊處置。

關鍵字

牙根柱 ； 三維有限元素法 ； 殘存齒質

並列摘要

Teeth with large proximal caries often need endodontic treatment. The non-vital teeth are often supported by use of posts. However, residual tooth structure has major influence on resistance of tooth fracture. Because of proximal caries, there is often compromised condition over mesial or distal side of teeth. Study for this situation is rare.
The purpose of this study was to analyze the stress of post and core for mandibular first premolar with different proximal decay during normal masticatory load by finite element method (FEM). Solid models of the mandibular first premolar with different tooth structure: original (A), 1 mm mesial defect (A1), 2 mm mesial defect (A2), 2 mm mesial defect with1 mm mesial defect (A21), 2 mm mesial defect with 2 mm mesial defect (A22), whole 0.5 mm defect (B), whole 1 mm defect (C), whole 1.5 mm defect (D), and whole 2 mm defect (E), and casting post was build up. Solid model was transferred to the mesh model in FE package (ANSYS) to process the stress analysis. Five different forces all 100 N were applied on buccal cusp tip: (1) LV: vertical force along tooth axis; (2) LB: 45 degree force from buccal to lingual direction. ; (3) LL: 45 degree force from lingual to buccal direction. ; (4) LM: 45 degree force from mesial to distal direction. ; (5) LD: 45 degree force from distal to mesial direction.
Under LV force, σ von Mises stress has little change on all root models, but σ von Mises stress and its position has some changes on all post models. Under lateral force, σ von Mises stress has little change on all models, except models D and E. The results show there should be at least 1 mm coronal tooth structure for resisting lateral force.

並列關鍵字

post ； finite element method ； residual tooth structure

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