基于三维有限元分析对无托槽隐形矫治器远中移动上颌尖牙的应力变化趋势初探

Preliminary study on stress variation trend of distal movement of maxillary canine with bracket-free invisible appliance based on three-dimensional finite element analysis

目的利用三维有限元分析方法对无托槽隐形矫治器远中移动上颌尖牙的应力变化趋势进行初步探索。方法选择2020年11月至2021年4月于四川大学华西口腔医院儿童口腔科就诊需远中移动上颌尖牙的患儿3例,分别诊断为前牙深覆、上颌牙列重度拥挤及上颌牙列拥挤+双侧上颌第二磨牙未萌,并根据锥形束CT(CBCT)数据构建三维有限元分析模型,分别记为第1~3例。3例三维有限元分析模型均模拟右上颌尖牙远中移动0.25、0.30、0.35、0.40、0.45 mm。利用ANSYS workbench 2020 R2软件分析初戴无托槽隐形矫治器时,右上颌尖牙牙体、牙周膜、牙槽骨和矫治器的应力分布,将最大应力值与移动距离进行直线、对数与指数回归分析,并通过决定系数R2选择最佳回归分析模型。结果(1)牙周膜应力分布:3例三维有限元分析模型右上颌尖牙牙周膜的最大应力值与移动距离存在直线、对数与指数回归关系,其中对数回归分析模型的R2值最大。(2)牙体应力分布:第1例和第3例三维有限元分析模型右上颌尖牙牙体的最大应力值与移动距离存在直线和对数回归关系,其中对数回归分析模型的R2值较大。(3)牙槽骨应力分布:第1例三维有限元分析模型牙槽骨的最大应力值与移动距离存在直线、对数与指数回归关系,其中对数回归分析模型的R2值最大。(4)矫治器应力分布:3例三维有限元分析模型矫治器的最大应力值与移动距离存在直线、对数与指数回归关系,且第1~3例分别为指数回归模型、对数回归模型及直线回归模型的R2值最大。结论在无托槽隐形矫治器远中移动上颌尖牙0.25~0.45 mm时,牙体、牙周膜及牙槽骨的最大应力值与移动距离很可能为对数回归关系,提示增加过矫治量对牙体、牙周膜及牙槽骨的应力变化影响较大,需要对移动距离进行精确计算与设计。此外,无托槽隐形矫治器的最大应力值与移动距离的回归关系并不惟一,提示其变化趋势可能与错畸形的类型有关。

Objective To explore the stress change trend of distal movement of the maxillary canines with the bracketfree invisible appliances by three-dimensional finite element analysis method.Methods Three children requiring distal movement of maxillary canine were selected in Department of Pediatric Dentistry,West China Hospital of Stomatology,Sichuan University from November 2020 to April 2021,who were respectively diagnosed with deep overbite of anterior teeth,severely crowded maxillary dentition and crowded maxillary dentition+bilateral maxillary second molars not erupted.Three-dimensional finite element analysis models were established based on cone-beam CT(CBCT)data,which were recorded as the first to third case.The above models were used to simulate the distal movement of the right maxillary canine at 0.25,0.30,0.35,0.40 and 0.45 mm,respectively.Analyze the stress distribution of the right maxillary canine,periodontal membrane,alveolar bone,and bracket-free invisible appliances when each set of invisible appliances without brackets was first worn by ANSYS workbench 2020 R2 software.The maximum stress value and the moving distance were analyzed by linear,logarithmic and exponential regression,and the optimal analysis model was selected through the determination coefficient R2.Results(1)Stress distribution in periodontal membrane:There was linear,logarithmic and exponential regression relationships between the moving distance and the maximum stress values of the right maxillary canine′s periodontal membrane of three models,and the R2 of the logarithmic regression model was the largest.(2)Stress distribution of teeth:The linear and logarithmic regression relationships existed between the moving distance and the maximum stress values of the right maxillary canine of the first and third case,and the R2 of the logarithmic regression model was the largest.(3)Stress distribution in alveolar bone:The linear,logarithmic and exponential regression relationships existed between the moving distance and the maximum stress values of alveolar bone in the first model,and the R2 of the logarithmic regression model was the largest.(4)Stress distribution of appliance:The linear,logarithmic and exponential regression relationships existed between the moving distance and the maximum stress values of the appliance in the 3 models.The R2 of exponential regression model,logarithmic regression model and linear regression model was the largest for case 1,case 2 and case 3,respectively.Conclusion It is likely that there is logarithmic regression relationship between the movement distance and the maximum stress value of maxillary canines,periodontal membrane and alveolar bone in the distal movement of the maxillary canines with the bracket-free invisible appliances in the range of 0.25-0.45 mm.It indicates that the increase of overcorrection movement distance has a great influence on the stress distribution of teeth,periodontal membrane and alveolar bone,so it is necessary to calculate and design the movement distance accurately.In addition,the regression relationship between the largest stress value of bracket-free appliances and the movement distance is not the only one,which suggests that the change trend may be related to the type of malocclusion.