无托槽隐形矫治器联合微种植钉牵引内收上前牙的三维有限元研究

Three-dimensional finite element analysis of retracting maxillary anterior teeth with clear aligner combined with miniscrew

目的:研究使用无托槽隐形矫治器治疗拔牙病例时,在关闭间隙阶段辅助种植钉与尖牙长牵引钩间200g弹性牵引时,前后牙的位移、牙周膜应力变化情况,为无托槽隐形拔牙矫治生物力学设计提供理论依据。方法:获取志愿者上颌骨CT数据,利用Mimics、Geomagic、Unigraphics NX等建立减数第一前磨牙的三维有限元模型,在Abaqus中加载并计算,分析厚度为0.4mm的无托槽隐形矫治器在整体回收前牙0.2mm时,不设计牵引(工况一)及第二前磨牙近中支抗与尖牙长牵引钩(power-arm)进行200g弹性牵引时(工况二),各牙牙周膜应力分布和位移趋势的变化规律。结果:单纯内收前牙时,切牙呈舌向倾斜移动伴伸长,中切牙舌倾0.378°、侧切牙舌倾0.444°、尖牙远中倾斜0.674°,第一磨牙近中倾斜0.27°;应力集中位于颈部及根尖区。工况二中各牙移动量及倾斜移动趋势均减小:各牙切端/牙尖位移减小25.13%(尖牙)~54.46%(侧切牙),倾斜角度减小25.93%(第一磨牙)~31.75%(尖牙),尖牙呈远中舌向倾斜;颈部及根尖区的牙周膜应力均有减小,最大等效应力减小约25.67%。结论:无托槽隐形矫治器在前牙整体内收关闭间隙时,联合种植支抗与尖牙间牵引可在一定程度上减少前牙及前磨牙的倾斜移动,对抗前牙垂直向伸长,保护磨牙支抗,同时减轻牙周膜应力。

Objective:To study the changes in the displacement of anterior and posterior teeth and the stress of periodontal ligament during the elastic traction of 200g between the miniscrews and power-arms on canine in the stage of closing the space when using the clear aligners to treat extraction cases,so as to provide a theoretical basis for the biomechanical design of clear aligner therapy.Methods:The CT data of the maxilla were obtained from a volunteer.Mimics,Geomagic and Unigraphics NX were used to establish a three-dimensional finite element model,which was loaded and calculated in Abaqus.The stress distribution of periodontal ligament and displacement trend of teeth were analyzed when the clear aligner with a thickness of 0.4mm was used to retract the anterior teeth for 0.2mm without involving the traction and when 200g elastic traction between miniscrews mesial to the second premolar and the power-arm on canine were used.Result:When the anterior teeth were retracted,the incisors were lingually tilted with elongation,the central incisors lingually tilted 0.378°,the lateral incisors lingually tilted 0.444°,the canines distally tilted 0.674°and the first molars mesially tilted 0.27°.The stress concentration was located in the cervical and apical regions.In the experimental group,after adding 200g traction between miniscrews and canines,the movement amount and inclination movement trend of each tooth was reduced:the displacement of each tooth was reduced by about 25.13%(canines)to 54.46%(lateral incisors).The angle of inclination is reduced by about 25.93%(first molars)to 31.75%(canines).The stress of the periodontal ligament in the cervical and apical regions decreased,and the range of stress concentration also decreased accordingly.The maximum equivalent stress decreased by about 25.67%.Conclusion:When the clear aligner therapy is used to close the space of the anterior teeth,adding elastic traction between power-arms and miniscrews can reduce the oblique movement of anterior teeth and premolars,resist the vertical extension of anterior teeth,protect the anchorage of molars,and reduce the stress of periodontal ligament.