上颌中切牙冠根折行冠延长术并桩核冠修复的三维有限元分析

Finite element analysis of the maxillary central incisor with crown lengthening surgery and post-core restoration in management of crown-root fracture

目的：构建上颌中切牙及其不同冠根折类型牙冠延长术后桩核冠修复的三维有限元模型,研究术后牙齿应力大小和分布情况,从力学角度分析牙冠延长术的适应征。方法：采用Micro-CT和3shape D700牙齿印模扫描仪分别对1颗上颌中切牙和模拟牙槽骨外形的石膏模型进行扫描,应用Mimics 10.0、Geomagic studio 9.0和ANSYS14.0软件构建上颌中切牙及其9种冠根折类型牙冠延长术后桩核冠修复的三维有限元模型。在舌侧切1/3和中1/3交界处,与牙长轴呈45°角静态加载100 N的力,对比分析不同模型中牙本质、牙周膜、牙槽骨、桩、核的等效应力（von Mises stress）和牙周膜面积的改变。结果：共建立10个精度较高的上颌中切牙三维有限元模型;不同牙冠延长术模型中不同结构的等效应力大小为：桩〉牙本质〉牙槽骨〉核〉牙周膜,且随着折裂程度的增加,上述结构的等效应力均呈线性增加（核例外）;模型的牙周膜面积减少了12%~33%;其中B2L2c、B2L3c、B3L1c、B3L2c、B3L3c模型的牙周膜等效应力超过了牙周膜的极限阈值。结论：唇侧折裂大于冠长3/4同时舌侧折裂深达骨嵴顶根方1 mm以上的上前牙不是牙冠延长术的良好适应征。

Objective： To construct the finite element models of maxillary central incisor and the simu- lations with crown lengthening surgery and post-core restoration in management of different crown-root fracture types, to investigate the stress intensity and distributions of these models mentioned above, and to analyze the indications of crown lengthening from the point of view of mechanics. Methods： An extrac- ted maxillary central incisor and alveolar bone plaster model were scanned by Micro-CT and dental impression scanner （3shape D700 ） respectively. Then the 3D finite element models of the maxillary central incisor and 9 simulations with crown lengthening surgery and post-core restoration were constructed by Mimics 10.0, Geomagic studio 9.0 and ANSYS 14.0 software. The oblique static force （ 100 N） was applied to the palatal surface （ the junctional area of the incisal 1/3 and middle 1/3 ） , at 45 degrees to the longitudinal axis, then the yon Mises stress of dentin, periodontal ligament, alveolar bone, post and core, as well as the periodontal ligament area, were calculated. Results： A total of 10 high-precision three-dimensional finite element models of maxillary central incisor were established. The von Mises stress of models： post 〉 dentin 〉 alveolar bone 〉 core 〉 periodontal ligament, and the yon Mises stress increased linearly with the augmentation of fracture degree （besides the core）. The periodontal ligament area of the crown lengthening was reduced by 12% to 33%. The von Mises stress of periodontal ligament of the B2L2c, B2L3c, B3Llc, B3L2c, B3L3c models exceeded their threshold limit value, respective- ly. Conclusion： The maxillary central incisors with the labial fracture greater than three-quarter crown length and the palatal fracture deeper than 1 mm below the alveolar crest are not the ideal indications of the crown lengthening surgery.