不同牙槽骨高度的磨牙压低时牙周膜应力分析

目的：通过建立具有不同牙槽骨高度的上颌第一磨牙三维有限元模型，在压力载荷下，计算分析其牙周膜应力的大小和分布，为正畸治疗提供力学参考。方法：采用CT对上颌第一磨牙进行扫描，建立牙槽骨发生不均衡水平吸收的上颌第一磨牙的三维有限元数字模型，计算加载垂直向的压低力时，牙周膜应力的大小和分布。结果：当牙槽骨从正常高度降低3.5 mm时，加载产生的牙周膜应力增加平缓，高应力集中部位在根分叉处；而牙槽骨降低超过6.0 mm，根分叉部分暴露时，牙周膜应力明显增加，应力集中的部位转移至根尖及根1/3处。结论：当牙槽骨高度降低未超过6 mm时(牙槽骨吸收未超过根长的48%)，应根据牙槽骨的丧失程度来减小矫治力值；当牙槽骨高度降低6 mm以上时(牙槽骨吸收超过根长48%)，磨牙的根分叉完全暴露，则应显著减小矫治力值。

Initial stress in the periodontal membrane of maxillary first molar with different alveolar bone height by intrusion: 3-dimensional finite element analysis

PURPOSE: To establish the 3-D finite element models of maxillary first molar, and calculate the stress magnitude and distribution within the PDL of maxillary first molar when loaded with intrusion force. METHODS: Date from CT scanning image of the maxillary first molar was used to establish the 3-D finite element model of maxillary first molar. By simulating the horizontal unbalanced bone resorption model sequentially, the magnitude and distribution of PDL stress at these models were calculated under intrusion force. RESULTS: The 3-D finite element models of maxillary first molar were constructed. With constant decrease of alveolar bone height, stress of the PDL increased non-linearly. The stress in PDL changed slowly when alveolar bone height reduced from normal level to 3.5 mm, but it increased dramatically when the height of alveolar bone resorption exceeded 6.0 mm and root furcation was exposed. The high-stress concentrated in root furcation of maxillary first molar when root furcation had not been exposed, and it would be transfered to apex or one third of root length when root furcation had been exposed. CONCLUSIONS: With the sustained decrease of alveolar bone height (less than 6 mm), orthodontic force value should be reduced according to the degree of periodontal bone loss. When the alveolar bone loss reduces to more than 6 mm and the root furcation exposes completely, orthodontic force value should be reduced significantly.