无托槽隐形矫治技术减数正畸内收上前牙的附件设计三维有限元分析

Three-dimensional finite element analysis of attachment design in the clear aligner treatment of extraction and upper anterior teeth retraction

目的通过三维有限元分析在无托槽隐形矫治技术减数正畸内收上前牙中不同位置和形态的附件对支抗牙生物力学影响,为临床附件设计提供参考。方法研究于2022年5—8月在中国医科大学口腔医学院口腔正畸学教研室进行。基于1例上颌前突成人患者的锥形束CT资料建立拔除上颌第一前磨牙的无托槽隐形矫治模型。应用三维有限元分析方法,根据支抗牙附件的形态和位置分为1个对照组(NA组,无附件)和5个实验组,包括VM组(垂直矩形附件于颊侧近中)、VD组(垂直矩形附件于颊侧远中)、HM组(水平矩形附件于颊侧近中)、HD组(水平矩形附件于颊侧远中)及GO组(成组半椭圆形附件)。于支抗牙(第二前磨牙、第一磨牙和第二磨牙)施加2 N作用力后,分析各组支抗牙初始位移与牙周膜最大Von-Mises应力情况。结果在颊腭向上,各组支抗牙均发生牙冠腭向移动、牙根颊向移动。在近远中向上,在第二前磨牙和第一磨牙中,GO组、HD组、VD组、HM组、VM组轴倾量依次增加;在第二磨牙中,HD组轴倾量(12.322×10^(-4)mm)最小,GO组相对于其他实验组轴倾量最大,为18.311×10^(-4)mm;而NA组支抗牙相比于所有实验组具有更大的近远中轴倾量。在垂直方向上,各实验组第二前磨牙牙冠仅有颊尖为向移动,第一磨牙牙冠远中颊尖及近远中颊根根尖为向移动,第二磨牙的牙冠与牙根均表现为向移动。各组最大牙周膜Von-Mises应力均分布在牙颈部。相比于实验组,NA组支抗牙牙周膜最大Von-Mises应力均较大,而各实验组第二前磨牙牙周膜最大Von-Mises应力均高于牙周膜可承受的最大应力(0.026 MPa)。结论在应用无托槽隐形矫治技术减数正畸内收上前牙中,附件可有效减小支抗牙的近中倾斜移动趋势及牙周膜应力,且颊侧远中水平矩形附件的效果较佳,可提高三维控制支抗牙的能力;但在摘戴矫治器时要轻柔,注意保护牙周组织。

Objective To evaluate biomechanical effect of different attachments on anchorage teeth during anterior teeth retraction with clear aligner by means of three-dimensional finite element analysis.Methods The study was conducted from May to August,2022 in the Orthodontics Department of Stomatology Hospital Affiliated to China Medical University.Based on the CBCT data of an adult with maxillary protrusion,a clear aligner model was established by extracting maxillary first premolars.By means of three-dimensional finite element analysis,we analyzed the initial displacement of anchorage teeth(second premolar first molar and second molar)after a force of 2 N and the biggest Von-Mises stress of periodontal membrane,with no attachment group(NA)as the control group and mesial vertical rectangular attachments(VM),distal vertical rectangular attachments(VD),distal or mesial horizontal rectangular attachments(HM),distal horizontal rectangular attachments(HD)and grouped half-oval attachments(GO)assembled with the model as 5 experimental groups.Results In the buccal and lingual direction,each group showed palatal displacement of the anchorage teeth crowns but roots had buccal movement trend.In the mesial-distal direction,second premolar and first molar,the axial tilt in the GO group,HD group,VD group,HM group,and VM group increased in turn.In the second molar,the HD group had the smallest axial tilt(12.322×10^(-4)mm),while the GO group had the largest tilt when compared with other experimental groups(18.311×10^(-4)mm).Compared to all experimental groups,the NA group had a greater axial tilt.In the vertical direction,only the buccal apex of second premolar showed an elongation trend.The distal buccal apex of first molar crowns as well as mesial and distal buccal roots showed elongation trends.The crown and root of second molar showed an elongation trend.The maximum Von-Mises stress distribution of PDL was in the dental cervix in all groups.The maximal stress of the anchorage teeth in the control group was greater than that in the corresponding experimental group.In all experimental groups,the maximal Von Mises stress on the periodontal membrane of second premolar was higher than the maximal stress that the periodontal membrane could withstand(0.026 MPa).Conclusion In the clear aligner treatment of extraction and upper anterior teeth retraction,the attachment can effectively reduce the tendency of mesial inclination movement of the anchorage teeth and Von Mises stress.The effect of the buccal distal horizontal rectangular attachment is better,which can improve the ability of three-dimensional control of the anchorage teeth.When removing and wearing appliances,be gentle and pay attention to protecting the periodontal tissue.