State Key Laboratory of Oral Diseases and National Clinical Research Center for Oral Diseases, and Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
School of Basic Medical Sciences, Chengdu University, Chengdu, China.
Am J Orthod Dentofacial Orthop. 2023 May;163(5):628-644.e11. doi: 10.1016/j.ajodo.2022.02.018. Epub 2023 Feb 15.
Clear aligners (CAs) have attracted increasing attention from patients and orthodontists because of their excellent esthetics and comfort. However, treating tooth extraction patients with CAs is difficult because their biomechanical effects are more complicated than those of traditional appliances. This study aimed to analyze the biomechanical effect of CAs in extraction space closure under different anchorage controls, including moderate, direct strong, and indirect strong anchorage. It could provide several new cognitions for anchorage control with CAs through finite element analysis, further directing clinical practice.
A 3-dimensional maxillary model was generated by combining cone-beam computed tomography and intraoral scan data. Three-dimensional modeling software was used to construct a standard first premolar extraction model, temporary anchorage devices, and CAs. Subsequently, finite element analysis was performed to simulate space closure under different anchorage controls.
Direct strong anchorage was beneficial for reducing the clockwise occlusal plane rotation, whereas indirect anchorage was conducive for anterior teeth inclination control. In the direct strong anchorage group, an increase in the retraction force would require more specific anterior teeth overcorrection to resist the tipping movement, mainly including lingual root control of the central incisor, followed by distal root control of the canine, lingual root control of the lateral incisor, distal root control of the lateral incisor, and distal root control of the central incisor. However, the retraction force could not eliminate the mesial movement of the posterior teeth, possibly causing a reciprocating motion during treatment. In indirect strong groups, when the button was close to the center of the crown, the second premolar presented less mesial and buccal tipping but more intrusion.
The 3 anchorage groups showed significantly different biomechanical effects in both the anterior and posterior teeth. Specific overcorrection or compensation forces should be considered when using different anchorage types. The moderate and indirect strong anchorages have a more stable and single-force system and could be reliable models in investigating the precise control of future tooth extraction patients.
由于美观性和舒适性极佳，隐形矫治器（CA）越来越受到患者和正畸医生的关注。然而，由于其生物力学效应比传统矫治器更为复杂，用 CA 治疗拔牙患者具有一定难度。本研究旨在通过有限元分析，探讨不同支抗控制方式下 CA 在拔牙间隙关闭中的生物力学效应，包括中度、直接强支抗和间接强支抗，为 CA 支抗控制提供新的认知，进一步指导临床实践。
通过锥形束 CT 和口内扫描数据的组合生成三维上颌模型。使用三维建模软件构建标准第一前磨牙拔牙模型、临时支抗装置和 CA。然后，通过有限元分析模拟不同支抗控制下的空间关闭。
直接强支抗有利于减少牙合平面顺时针旋转，而间接支抗有利于控制前牙倾斜。在直接强支抗组中，增加收合力需要对前牙进行更多特定的过矫正以抵抗倾斜运动，主要包括中切牙舌侧根控制，其次是尖牙远中根控制、侧切牙舌侧根控制、侧切牙远中根控制和中切牙远中根控制。然而，收合力不能消除后牙的近中移动，可能导致治疗过程中的往复运动。在间接强支抗组中，当按钮接近牙冠中心时，第二磨牙近中颊向倾斜和颊舌向转矩较小，但更多的内收。
三种支抗组在前牙和后牙中表现出明显不同的生物力学效应。使用不同的支抗类型时，应考虑特定的过矫正或补偿力。中度和间接强支抗具有更稳定和单一的力系统，可能是研究未来拔牙患者精确控制的可靠模型。
