State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Orthodontics, School of Stomatology, Air Force Medical University, Xi'an, 710032, China.
Urumql DW Innovation InfoTech Co., Ltd, Xinjiang, 830000, China.
Prog Orthod. 2022 Aug 1;23(1):26. doi: 10.1186/s40510-022-00421-8.
Clear aligner treatment has become popular over recent years. It is necessary to identify methods by which we could avoid the bowing effect in extractions with clear aligner. The present study was to identify the appropriate method to design torque movement involving the upper anterior teeth of extraction cases, in order to maintain or improve the axis and torque of the upper anterior teeth with a clear aligner during movement and closure of the extraction space.
As the height of the power ridge increased, the rotation angle of the upper central incisor in the sagittal direction decreased gradually and the location of the rotation center changed significantly; the rotation center moved in the apical direction and then changed to the crown side. The highest von-Mises stress of the upper central incisor root, periodontal ligaments, and alveolar bone, showed little change as the power ridge height increased. When the axial inclination of the upper central incisor was normal (U1-SN = 105°), the tendency of movement for the upper central incisor approached translation with a power ridge height of 0.7 mm (corresponding distorted angle: 5.8415). When the axial inclination of the upper central incisor was oversized (U1-SN = 110°), the axial inclination of the upper central incisor reduced to normal following completion of the anterior segment retraction with a power ridge of 0.4 mm (corresponding distorted angle: 3.4265).
Analysis indicates that pure palatal tipping movement of the upper anterior teeth is generated without torque control, thus resulting in the bowing effect. The required torque control of the upper anterior teeth with oversize axial inclination is weaker than that of the upper anterior teeth with normal axial inclination because limited torque loss is expected for oversize axial inclination teeth. Variation sensitivity of the rotation center should be considered carefully due to biological problems when designing translation of the upper anterior teeth with normal axial inclination.
近年来，透明牙套矫正治疗已变得流行。有必要寻找方法避免在使用透明牙套进行拔牙矫正时发生弓丝弯曲。本研究旨在找到一种合适的方法，设计拔牙病例上前牙的转矩移动，以便在使用透明牙套关闭拔牙间隙时保持或改善前牙的轴倾度和转矩。
随着动力曲高度的增加，上颌中切牙矢状向的旋转角度逐渐减小，旋转中心的位置变化显著；旋转中心向根尖方向移动，然后向冠方移动。随着动力曲高度的增加，上颌中切牙牙根、牙周膜和牙槽骨的von-Mises 等效应力最高值几乎没有变化。当上颌中切牙轴倾角正常（U1-SN=105°）时，随着动力曲高度为 0.7mm（对应扭曲角：5.8415°），上颌中切牙的运动趋势接近平移。当上颌中切牙轴倾角过大（U1-SN=110°）时，上颌中切牙的轴倾角在使用 0.4mm 动力曲（对应扭曲角：3.4265°）完成前段内收后减小至正常。
分析表明，上颌前牙在没有转矩控制的情况下发生纯腭向倾斜运动，从而导致弓丝弯曲。轴向倾斜过大的上颌前牙所需的转矩控制比轴向倾斜正常的上颌前牙弱，因为预计轴向倾斜过大的牙齿会有有限的转矩损失。在设计轴向倾斜正常的上颌前牙平移时，由于生物问题，应仔细考虑旋转中心的变化敏感性。
