Department of Orthodontics, School of Stomatology, State Key Laboratory of Military Stomatology & National Clinical Research Center for Oral Diseases & Shaanxi Clinical Research Center for Oral Diseases, Air Force Medical University, Xi'an, 710032, China.
Urumql DW Innovation InfoTech Co.Ltd, Xinjiang, 830000, China.
BMC Oral Health. 2022 Dec 1;22(1):546. doi: 10.1186/s12903-022-02526-2.
The effects of upper-molar distalization using clear aligners in combination with Class II elastics for anchorage reinforcement have not been fully investigated yet. The objective of this study is to analyze the movement and stress of the whole dentition and further explore guidelines for the selection of traction methods.
Three-dimensional (3D) finite element models are established to simulate the sequential molar distalization process, including the initial distalization of the 2 molar (Set I) and the initial distalization of the 1 molar (Set II). Each group set features three models: a control model without Class II elastics (model A), Class II elastics attached to the tooth by buttons (model B), and Class II elastics attached to the aligner by precision cutting (model C). The 3D displacements, proclination angles, periodontal ligament (PDL) hydrostatic stress and alveolar bone von Mises stress in the anterior area are recorded.
In all of the models, the maxillary anterior teeth are labial and mesial proclined, whereas the distal moving molars exhibit distal buccal inclination with an extrusion tendency. With the combination of Class II elastics, the anchorage was effectively reinforced; model C demonstrates superior anchorage reinforcement with lower stress distribution in comparison with model B. The upper canines in model B present an extrusion tendency. Meanwhile, the mandibular dentition in models B and C experience undesired movement tendencies with little discrepancy from each other.
Class II elastics are generally effective for anchorage reinforcement as the upper-molar distalization is performed with clear aligners. Class II elastics attached to an aligner by precision cutting is a superior alternative for maxillary anchorage control in cases that the proclination of upper incisors and extrusion of upper canines are unwanted.
使用透明牙套结合 II 类弹性体进行支抗加强来远移上颌磨牙的效果尚未得到充分研究。本研究旨在分析整个牙齿的运动和受力情况，并进一步探讨牵引方法选择的指导原则。
建立三维（3D）有限元模型来模拟磨牙的顺序远移过程，包括第二磨牙的初始远移（Set I）和第一磨牙的初始远移（Set II）。每组都设有三个模型：不使用 II 类弹性体的对照模型（模型 A）、通过按钮将 II 类弹性体附接到牙齿的模型（模型 B）和通过精密切割将 II 类弹性体附接到牙套的模型（模型 C）。记录了 3D 位移、倾斜角、牙周膜（PDL）静水压力和前牙区牙槽骨 von Mises 应力。
在所有模型中，上颌前牙唇侧和近中倾斜，而远移磨牙表现出远中颊向倾斜和外展趋势。结合 II 类弹性体可有效加强支抗，与模型 B 相比，模型 C 显示出更好的支抗加强效果和更低的应力分布。模型 B 中的上颌尖牙有外展趋势。同时，模型 B 和 C 中的下颌牙齿呈现出不期望的运动趋势，但彼此之间差异不大。
使用透明牙套远移上颌磨牙时，II 类弹性体通常可有效加强支抗。当不希望上颌切牙倾斜和上颌尖牙外展时，通过精密切割将 II 类弹性体附接到牙套上是一种更好的上颌支抗控制替代方法。
