不同大小颏兜牵引力的下颌骨三维有限元分析

THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF THE MANDIBLE UNDER DIFFERENT ORTHOPEDIC CHINCUP FORCES

目的 :用三维有限元法分析不同大小颏兜后上牵引力作用下髁突软骨和下颌骨的应力分布和位移 ,探讨颏兜的作用机制。方法 :在建立的“TMJ -下颌骨 -颏兜矫形系统”三维有限元模型上 ,模拟颏兜加力 4 0 0 g和 1 0 0 0 g ,方向通过髁突中心 ,采用SuperSAP(93)非线性有限元分析软件进行计算和分析。结果 :①颏兜牵引力的大小不能改变髁突软骨表面的应力分布趋势 :前上部明显的压应力集中区 ,外上份出现以张应力为主的应力集中区 ;②颏兜牵引力的大小不能改变下颌骨及髁突的顺时针向旋转趋势 ,且牵引力的增大使其更明显 ;③颏兜牵引力使下颌骨顺时针向旋转的同时将使下颌骨发生变形 :下颌枝向前弯曲 ,下颌体向下弯曲 ,且牵引力越大旋转、变形越严重。结论 :通过髁突中心的颏兜牵引力无论其大和小 ,均难以抑制下颌髁突的生长 ,仅能改变下颌骨的生长方向 ,使其顺时针向旋转生长 ,同时下颌骨将可能发生一定的生长变形即下颌角增大。

Objective:To analyze the mechanism of the different chincup forces through the stress distribution of the mandible and the mandibular condylar cartilage.Methods:The three-dimensional finite element model of “TMJ-Chincup-Mandibular Orthopedic System” was constructed.The chincup forces of 400 g and 1000 g was given and the orientation of the force was from the chincup to the two condyles.The stress was analyzed using Super SAP(93)finite element software.Results: ①Different chincup forces did not change the stress distribution:compressive stress distribution in the anterior-upper region,tensive stress distribution in the up-outer region on the surface of the condylar cartilage.②Different chincup forces did not change the rotating displacement in clockwise of mandible.And the larger the forces were,the severer the rotation was.③Mandible deformed and mandibular body bended downwards under the chincup forces;and the larger the forces were,the severer the deformation was.Conclusion: The results indicate that the chincup forces,whether they are larger or smaller,are very difficult to retard the growth of mandible.They can only change the growth direction of mandible,and makes the mandible grow in clockwise rotating.