In the orthodontics process, intervention and sliding of an orthodontic bracket during the orthodontic process can arise large response of the labio-cheek soft tissue. Soft tissue damage and ulcers frequently happen at the early stage of orthodontic treatment. In the field of orthodontic medicine, qualitative analysis is always carried out through statistics of clinical cases, while quantitative explanation of bio-mechanical mechanism is lacking. For this purpose, finite element analysis of a three-dimensional labio-cheek-bracket-tooth model is conducted to quantify the bracket-induced mechanical response of the labio-cheek soft tissue, which involves complex coupling of contact nonlinearity, material nonlinearity and geometric nonlinearity. Firstly, based on the biological composition characteristics of labio-cheek, a second-order Ogden model is optimally selected to describe the adipose-like material of the labio-cheek soft tissue. Secondly, according to the characteristics of oral activity, a two-stage simulation model of bracket intervention and orthogonal sliding is established, and the key contact parameters are optimally set. Finally, the two-level analysis method of overall model and submodel is used to achieve efficient solution of high-precision strains in submodels based on the displacement boundary obtained from the overall model calculation. Calculation results with four typical tooth morphologies during orthodontic treatment show that: ① the maximum strain of soft tissue is distributed along the sharp edges of the bracket, consistent with the clinically observed profile of soft tissue deformation; ② the maximum strain of soft tissue is reduced as the teeth align, consistent with the clinical manifestation of common damage and ulcers at the beginning of orthodontic treatment and reduced patient discomfort at the end of treatment. The method in this paper can provide reference for relevant quantitative analysis studies in the field of orthodontic medical treatment at home and abroad, and further benefit to the product development analysis of new orthodontic devices.
牙齿正畸过程中，矫牙托槽的介入和滑动容易导致唇颊软组织出现较大反应，矫治初期常见软组织损伤和溃疡。口腔正畸医疗领域采用临床案例统计方法进行定性分析，缺乏生物力学机制的定量解释。为此，开展唇颊—托槽—牙齿的三维模型有限元分析，计算托槽引起的唇颊软组织的力学反应，其中涉及复杂耦合的接触非线性、材料非线性和几何非线性。首先，根据唇颊生物组成特点，优化选取二阶奥格登（Ogden）超弹性本构模型，对类脂肪材料的唇颊软组织进行表征。其次，根据口腔活动特点，建立托槽介入和正交滑动的两阶段仿真模型，并对关键接触参数进行优化设置。最终，采用整体模型—子模型的两层次分析方法，基于整体模型计算得到的位移边界，实现子模型高精度应变的高效求解。针对正畸过程中四种典型牙齿形态的计算结果表明：① 软组织最大应变沿托槽尖锐边缘分布，与临床观测的软组织变形轮廓一致；② 随着牙齿排齐，软组织的最大应变也随之减小，与矫治初期常见损伤和溃疡以及矫治后期患者不适感减轻的临床表现相符。本文的方法可为国内外口腔正畸医疗领域的相关量化分析研究提供参考，进一步有益于新型矫治装置的产品研发分析。.
Keywords: Contact; Labio-cheek soft tissue; Non-linear finite element; Orthodontic bracket; Submodel.