下顎第一小臼齒不同根柱直徑影響牙根齒質之應力分析－有限元素法

Biomechanical stress analysis of root structure of mandibular first premolar with different post diameter－finite element stress analysis

林威克(Wei-Ko Lin)

指導教授 ： 李惠娥

高雄醫學大學/口腔醫學院/牙醫學研究所/碩士(2005年)

摘要

研究指出無髓牙（pulpless）會變得較脆且易斷裂，因此部分學者認為於根管內置入根柱有助於根管治療後牙齒結構的強化。然而，對於所置入的根柱究竟應如何選擇尚無令人滿意的解答，尤其是對牙根斷裂之影響舉足輕重的根柱直徑更是缺乏有力的實驗數據做為臨床的參考。本研究的目的主要是利用電腦輔助分析與實驗驗證的方式，完整探討不同直徑的金屬鑄造根柱在不同方向的咬合力下，對牙根所造成的應力變化，以提供臨床診斷與治療參考之用。實驗以有限元素軟體（ANSYS）分析人類下顎第一小臼齒三維實體模型，模擬裝置不同直徑根柱（牙根直徑的0.2、0.3、0.4、0.5、0.6、0.8倍）受到不同方向咬合力時應力分布的變化，並找出最適當的根柱直徑。咬合力的設定均為100N且通過小臼齒頰阜頂點，P1表示和牙齒長軸垂直的咬合力、P2表示頰側45度方向的咬合力。結果發現無論是P1或P2的力量，最適合的根柱直徑皆為牙根直徑的0.5倍，應力集中於牙根冠部三分之一以及根柱中段。受到斜向力P2時，根柱頰側和牙根齒質交介面的張應力在直徑0.5倍以後逐漸增加，齒質本身則無甚大改變。本研究所得結論：最適當的根柱直徑為牙根直徑的0.5倍，而當根柱直徑大於牙根直徑的0.6倍以上時，需使用抗張強度較強的根柱材質。

關鍵字

牙根斷裂 ； 根柱 ； 三維有限元素法

並列摘要

Some reports point out the weakness of endodontically treated teeth, that it would reinforce the teeth by use of posts. However, it is questionable about how to select posts to fulfill most of clinical situations especially the post diameter which mainly influence the root fracture. The purpose of this study was to analyze the stress of casting post with different diameters during normal masticatory load by finite element method (FEM) and experimental strain measurement for validity test. Furthermore, attempt to find the best post diameter for clinical use. In this study, the three-dimensional finite element method was employed to analyze the stress difficult to calculate by traditional clinical observation or experimental approaches. Solid models of the mandibular first premolar with six diameter (0.2, 0.3, 0.4, 0.5, 0.6, 0.8 times of root diameter) of casting post was build up and then transferred to the mesh model in FE package(ANSYS) to process the stress analysis. Two different force were applied on buccal cusp tip: (1)P1: vertical force along tooth axis; (2)P2: 45 degree force from buccal direction. The results showed that the best diameter of post is 0.5 times of root and the stress concentrated on coronal third of root and middle third of post. We also found that the tensile stress of casting post increased with the wider post diameter after 0.5 times of root but not the root itself. The conclusions of this study were that the best post diameter was 0.5 times of root and we should use more strength post material when the post diameter was wider than 0.6 times of root.

並列關鍵字

root fracture ； post ； finite element method

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