Department of Orthodontics, State Key Laboratory of Oral Diseases & National Center for Stomatology & National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 Sichuan, China.
Department of Maxillofacial Orthognathics, Tokyo Medical and Dental University, Graduate School, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8510, Japan.
Int Orthod. 2024 Dec;22(4):100924. doi: 10.1016/j.ortho.2024.100924. Epub 2024 Sep 30.
To analyse the biomechanics of molar protraction through clear aligner therapy (CAT) with and without a buccal cantilever.
Models were composed of mandible, lower dentition, periodontal ligaments, attachments, a buccal cantilever, and clear aligner. Four groups were designed: (1) control (aligner only), (2) aligner+buccal cantilever with buccal class II traction, (3) aligner+buccal cantilever with buccal class II and lingual class II tractions, (4) aligner+buccal cantilever with buccal horizontal traction named buccal class I, buccal class II, and lingual class II tractions.
CAT alone caused mesial tipping, lingual tipping, and intrusion of mandibular second molar. Adding the buccal cantilever on the mandibular second molar with 100-g buccal class II traction was effective in preventing the mesial tipping of mandibular second molar, but resulted in a greater lingual tipping tendency. Further addition of lingual class II traction prevented aforementioned lingual tipping and bodily protraction was achieved in sagittal dimension, while buccal tipping was present. Bodily protraction without buccolingual tipping was achieved through clear aligner, buccal class II, lingual class II, and buccal class I tractions, and the stress concentrated on the alveolar bone was reduced.
CAT produced mesial tipping, lingual tipping, and intrusion of mandibular molar during protraction. The incorporation of the buccal cantilever into the clear aligner improves the biomechanical effect of molar protraction. Bodily molar protraction can be achieved with a judicious combination of buccal class II, lingual class II and buccal class I tractions with clear aligner and buccal cantilever.
分析通过透明牙套正畸治疗（CAT）并结合颊向支抗和不结合颊向支抗来实现磨牙远中移动的生物力学。
模型由下颌骨、下颌牙列、牙周韧带、附件、颊向支抗和透明牙套组成。设计了四个组：（1）对照组（仅牙套）、（2）牙套+颊向支抗，用于颊向二类牵引、（3）牙套+颊向支抗，用于颊向二类和舌向二类牵引、（4）牙套+颊向支抗，用于颊向水平牵引，称为颊向二类、颊向二类和舌向二类牵引。
CAT 单独使用会导致下颌第二磨牙近中倾斜、舌向倾斜和压低。在下颌第二磨牙上添加 100g 的颊向二类牵引的颊向支抗可有效防止下颌第二磨牙的近中倾斜，但会导致更大的舌向倾斜趋势。进一步增加舌向二类牵引可防止上述舌向倾斜，并在矢状方向上实现牙体的远中移动，同时存在颊向倾斜。通过透明牙套、颊向二类、舌向二类和颊向一类牵引实现无颊舌向倾斜的牙体远中移动，同时减少牙槽骨上的应力集中。
CAT 在牵引过程中会导致下颌磨牙的近中倾斜、舌向倾斜和压低。颊向支抗结合透明牙套可改善磨牙远中移动的生物力学效果。通过透明牙套和颊向支抗，合理结合颊向二类、舌向二类和颊向一类牵引，可以实现磨牙的远中移动。
