三种快速扩弓联合前方牵引装置作用效果的三维有限元分析

Effects of three types of rapid maxillary expansion with protraction appliances:A three-dimensional finite element analysis

目的应用三维有限元法比较三种快速扩弓联合前方牵引装置对颌骨及牙齿的作用效果,为临床治疗提供参考。方法建立Hyrax联合牙性前方牵引装置、骨支持式扩弓器(maxillary skeletal expander,MSE)联合牙性前方牵引装置、MSE联合骨性前方牵引装置及颅上颌复合体的三维有限元模型,对扩弓螺旋器施加0.25 mm的横向位移并于装置牵引位点施加大小为500 g/侧的牵引力,力的方向与咬合平面呈30°向下,分析三种快速扩弓联合前方牵引装置作用下的颌骨及牙齿的位移趋势及应力分布。结果三种装置作用下的颌骨应力分布及位移趋势相似,但两种MSE联合前方牵引装置作用下的颌骨横向位移量为Hyrax联合前方牵引装置位移量的2.7倍,矢状向的位移量为Hyrax联合前方牵引装置的2.6倍,颌骨的应力值远大于Hyrax联合前方牵引装置;三个模型的牙齿位移趋势相似,但牙齿应力分布模式不同,MSE联合骨性前方牵引装置对于磨牙仍有作用力。结论(1)对于需要大的颌骨移动量及错过生长发育的患者可选择骨性快速扩弓前方牵引装置。(2)MSE联合前方牵引装置仍需改进。

Objective To evaluate the effects of three kinds of rapid maxillary expansion with protraction appliances on maxilla and teeth using three-dimensional finite element method,and provide reference for clinical treatment.Methods The three-dimensional finite element model of Hyrax with tooth-borne protraction appliance,MSE(Maxillary Skeletal Expander)with tooth-borne protraction appliance,MSE with bone-borne protraction appliance and cranial-maxillary complex was established.The expander screw was activated by 0.25 mm and the traction force of 500 g per side was applied to the traction site of the appliance.The direction of the force was 30°downward and forward to the occlusion plane.The displacement trend and stress distribution of maxilla and teeth under the three kinds of appliances were evaluated.Results The stress distribution and the displacement trend of the three types of appliances were similar,but the lateral displacement of the maxilla under the two kinds of MSE with protraction appliance was 2.7 times as much as that of the Hyrax’s,and 2.6 times in sagittal displacement,and its stress value was much higher than that of the Hyrax’s.The tooth displacement trend of the three models was similar,but the tooth stress distribution pattern was different.MSE with bone-borne protraction appliance still affected the anchored molar.Conclusion(1)MSE with protraction appliance is a better choice for adults or patients who need a large amount of maxilla movement.(2)MSE with protraction appliance needs to be improved.