目的： 建立K锉、H锉和Protaper锉的三维有限元模型，分析其在弯曲根管中发生扭转断裂的原因与机制。方法 运用软件Pro/Engineer 5.0建立25号不锈钢K锉、25号不锈钢H锉及Protaper F1锉切割刃全长的三维有限元模型；根据不同的弯曲角度和弯曲半径将其分为4组：30°/5 mm、30°/2 mm、45°/5 mm及45°/2 mm组，运行Pro/Mechanica有限元分析软件进行力量加载分析，观察顺螺纹及逆螺纹扭转负载下锉刃各部位的应力分布。结果 K锉和H锉在顺螺纹和逆螺纹2种受力条件下应力分布没有差别。K锉在45°/2 mm组的应力集中点位于切割刃尖；H锉在30°/5 mm和45°/5 mm组最大应力部位位于两切削刃的沟槽内，而在30°/2 mm和45°/2 mm组最大应力部位位于切削刃尖部，应力集中部位与扭转方向无关联；而在Protaper F1锉组中，30°/2 mm和45°/5 mm组的最大应力部位在两切削刃的沟槽内，其余组的均位于切削刃尖部。结论 K锉和Protaper锉的对称截面设计有利于分散应力，而H锉的非对称截面设计易发生应力集中，在弯曲根管中受扭转负载时，后者更易断裂。%Objective This study aimed to establish finite element analysis(FEA) models of the K file, H file, and Protaper file, and analyze the factors leading to the breakdown of these instruments when used in curved root canal. Methods Using the software Pro/Engineer 5.0, we generated three-dimensional FEA models of the cutting edges of the stainless steels K file, H file, and Ni-Ti Protaper file. Curved root canals were classified into four groups according to the angle and radius of the curvature: 30°/5 mm, 30°/2 mm, 45°/5 mm, and 45°/2 mm. Pro/Mechanica software performed the FEA on the mechanism of the working instrument in a curved root canal. Stress distribution in the cutting edges under clockwise and counterclockwise torsional loads was analyzed. Results Similar stress distribution patterns were observed in K and H file groups regardless of the direction of torsional load, either clockwise or counter clockwise. In the 45°/2 mm group, stress on the K file is concentrated at the tip of the cutting blade. However, in 30°/5 mm and 45°/5 mm groups, stress on the H file is concentrated at the groove between two cutting edges, whereas in 30°/2 mm and 45°/2 mm, maximum stress is located at the tip of the cutting edge, stress positions and no good or bad times to reverse the direction of the association. In F1 Group, maximum stress is located at the cutting edge tip, in addition to groups(i.e., 45°/5 mm and 30°/2 mm) where stress is acting on the groove between two cutting edges. Conclusion The symmetric cross-section design of the K file and Protaper file is beneficial in the distribution of stress, while the non-symme triccross-section design of the H file is prone to create uneven stress distribution. Thus, the latter is easier to break when used in a curved root canal and under torsional load.
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