无托槽隐形矫治整体内收减数正畸患者前牙的三维有限元分析

Three-dimensional finite element analysis on en-mass retraction of anterior teeth with clear aligner

目的通过三维有限元法模拟无托槽隐形矫治整体内收减数正畸患者上前牙的过程,探讨整个矫治系统的力学效应,为正畸临床提供参考。方法选择1例减数上颌双侧第一前磨牙且上颌牙列已排齐整平的女性正畸患者(就诊于重庆医科大学附属口腔医院正畸科,26岁),采用锥形束CT进行扫描,通过Mimics 17.0、SolidWorks 2016、Geomagic Studio 2015等软件建立包含上颌牙齿、牙周膜、牙槽骨和无托槽隐形矫治器的三维有限元模型,导入Abaqus 6.14软件,以非线性接触法模拟配戴无托槽隐形矫治器整体内收前牙0.2 mm的过程,分析上颌牙移动趋势及位移、牙周膜及牙槽窝的应力分布以及矫治器的变形趋势。结果前牙内收过程中牙冠均有舌侧偏远中倾斜移动伴覆加深的趋势,中切牙、侧切牙和尖牙的最大位移分别为25.16、50.34和24.98μm;第二前磨牙、第一磨牙、第二磨牙牙冠均有近中倾斜移动的趋势,最大位移分别为33.04、2.90和16.63μm。牙周膜及牙槽窝应力分布与牙移动趋势相符,拔牙间隙两侧牙周膜应力较大且在牙槽窝根尖处出现应力集中。无托槽隐形矫治器在邻牙连接处应力较大,并有向脱落的趋势。结论应用无托槽隐形矫治器整体内收前牙时,应注意前牙控根、压低以及后牙支抗的保护,同时应警惕拔牙间隙两侧牙齿出现牙根吸收。

Objective To investigate the mechanical effects during en-mass retraction of maxillary anterior teeth with clear aligner using three-dimensional finite element method.Methods Cone-beam CT(CBCT)was used to scan a female orthodontic patient(26 years old,from Department of Orthodontics,Stomatological Hospital of Chongqing Medical University)whose maxillary first premolars were extracted and maxillary dentition had been aligned and leveled.A finite element model including maxillary teeth-periodontal ligament(PDL)-alveolar bone-clear aligner was established by using Mimics 17.0,SolidWorks 2016 and Geomagic Studio 2015 software packages.The process of 0.2 mm en-mass retraction of anterior teeth using clear aligner was simulated by using non-linear contact method of Abaqus 6.14.The trend and displacement of maxillary teeth,the stress distribution of PDL and alveolar fossae,and the deformation trend of clear aligner were obtained and analyzed.Results Under the experimental condition,lingual crown tipping and distal tipping movement of anterior teeth were observed,and all of them had the tendency of overbite increasing.The maximum displacement of the central incisor,lateral incisor and canine were 25.16,50.34 and 24.98μm,respectively.Meanwhile,the second premolar,first molar and second molar had the tendency of mesial tipping movement,and the maximum displacement of them were 33.04,2.90 and 16.63μm,respectively.The stress distribution both at the PDL and alveolar fossae were consistent with tooth movement pattern.It was noted that the stress in the PDL of the canine and second premolar were comparatively big,and the corresponding apical areas of alveolar fossae appeared stress concentration.Concurrently,it was found that the clear aligner showed stress concentration at the junction of adjacent teeth with a tendency of crown directional dislocation.Conclusions During en-mass retraction of anterior teeth with clear aligner,attention should be paid to the overbite and torque in anterior teeth,and the anchorage protection of posterior teeth.At the same time,we should be careful of root resorption of the teeth on both sides of the extraction space.