NRT FILES镍钛根管锉预备对弯曲根管应力分布的仿真分析

Simulation analysis of stress distribution of NRT FILES in curved root canals

背景:在根管治疗中,镍钛合金器械常因应力超过金属塑性变形的弹性极限或在根管弯曲处重复弯曲导致镍钛合金疲劳断裂。目的:探索新型镍钛锉NRT FILES在作为根管预备材料时对根管内壁存在的应力分布,明确应力集中区域。方法:利用Solidworks软件对NRT FILES进行三维建模,模拟还原器械在真实口腔环境中存在的状态。建立6组根管简化模型:①弯曲角度30°、弯曲半径5 mm、根尖弯曲;②弯曲角度30°、弯曲半径5 mm、根中弯曲;③弯曲角度30°、弯曲半径2 mm、根尖弯曲;④弯曲角度30°、弯曲半径2 mm、根中弯曲;⑤弯曲角度45°、弯曲半径5 mm、根尖弯曲;⑥弯曲角度45°、弯曲半径2 mm、根尖弯曲。将根管简化模型与根管锉模型进行组配,对根管内壁受力点及应力分布情况进行分析。结果与结论:①-⑥组根管锉最大应力分别为1 185,1 354,1 371,1 678,1 335,2 557 MPa,最大应变分别为0.010 36,0.013 54,0.013 79,0.016 48,0.013 45,0.022 03;根管弯曲部位的不同会影响根管锉所承受的应力大小,因此在根管治疗中,根管锉沿着根管越往下,根管锉与根管接触的半径越大、刚性越差,根管锉所承受的应力越大越容易发生断裂;根管弯曲半径越小,根管锉承受的应力越大;根管弯曲角度越小,根管锉所承受的应力越大。在根尖弯曲部位,根管锉在根管弯曲半径小的弯曲根管需要承受更大的应力,根管锉更容易发生断裂;同理,在根中弯曲部位,根管锉在根管弯曲半径小的弯曲根管亦承受更大的应力,因此要格外注意根管的弯曲程度,以此来选择合适的根管锉进行根管治疗。

BACKGROUND: In root canal therapy, the fatigue fracture of NiTi alloy instruments is often caused by stress exceeding the elastic limit of metal plastic deformation or repeated bending at the root canal bend.OBJECTIVE: To explore the stress distribution on the inner wall of root canals when NRT FILES are used as root canal preparation materials, and to examine the stress concentration area.METHODS: Solidworks software was used for 3D modeling of NRT FILES to simulate the state of the instruments in real oral environment. Six groups of simplified root canal models were established:(1) Bending angle of 30°, bending radius of 5 mm, root apex bending;(2) Bending angle of 30°, bending radius of 5 mm, middle root bending;(3) Bending angle of 30°, bending radius of 2 mm, root apex bending;(4) Bending angle of 30°, bending radius of 2 mm, middle root bending;(5) Bending angle of 45°, bending radius of 5 mm, root apex bending;(6) Bending angle of 45°, bending radius of 2 mm, root apex bending. The simplified root canal model and the root canal file model were assembled, and the stress points and stress distribution on the inner wall of the root canal were analyzed.RESULTS AND CONCLUSION: The maximum stresses of root canal files in groups(1)-(6) were 1 185, 1 354, 1 371, 1 678, 1 335, and 2 557 MPa, and the maximum strains were 0.010 36, 0.013 54, 0.013 79, 0.016 48, 0.013 45, and 0.022 03, respectively. Different bending parts of root canals could affect the stress borne by the root canal file. In root canal therapy, the lower the root canal file went down along the root canal, the greater the contact radius between these two pieces, the worse the rigidity of the root canal file, the greater the stress it bore, and the easier it was to fracture. The smaller the root canal bending radius, the greater the stress bore on the root canal file. The smaller the bending angle of the root canal, the greater the stress on the file. In the curved part of the root canal tip, the root canal file bore greater stress when the bending radius of the root canal was small, and it was more prone to fracture;similarly, in the curved part of the middle of root canal, the root canal file also bore greater stress with small bending radius. Therefore, it is necessary to pay extra attention to the bending degree of the root canal and select an appropriate root canal file for root canal treatment.