Liu Xulin, Wang Wei, Gao Jie, Qin Wen, Wen Yi, Luo Houzhuo, Ma Yanning, Jin Zuolin
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, China.
Shanxi Medical University School and Hospital of Stomatology, Taiyuan, China.
Am J Orthod Dentofacial Orthop. 2023 Oct;164(4):e106-e120. doi: 10.1016/j.ajodo.2023.07.007. Epub 2023 Aug 20.
Class II elastics, in combination with clear aligners (CA), are efficient for molar distalization. However, the effects of this combination on intermaxillary molar relationship correction have yet to be investigated. This study aimed to investigate the actual contribution ratio of the maxillary and mandibular molars for total molar relationship correction during maxillary molar distalization using Class II elastics with CA and further explore therapeutic recommendations for clinical practice.
Finite element models (FEMs) were established, including the distalization of the second molars (Set I), followed by the distalization of the first molars (Set II). Model A simulated elastics attached by precision cutting, whereas Model B simulated elastics attached to buttons. Force magnitudes of 100 g, 150 g, and 200 g of force were applied. We recorded the contribution ratio of the maxillary and mandibular molars for total molar relationship correction, effective distalizing distance in 0.25 mm step distance, tipping and rotation angles, and the hydrostatic stress in the periodontal ligament.
During maxillary molar distalization, mesialization of the mandibular molar had a notable contribution ratio for molar relationship correction. The mandibular first molar was mesialized with mesiolingual rotation tendency. Approximately half of the 0.25 mm step distance was occupied by maxillary molar distalization; the remainder was occupied by anchorage teeth mesialization and tipping or rotation. When traction forces increased, the total molar relationship correction and effective distalization increased; the mandibular molars mesialization contribution ratio also increased, as did rotation and inclination tendency. Precision cutting had a higher total molar relationship correction and more effective distalization than a button but also had a larger contribution ratio of mandibular molar mesialization and inclination or rotation.
Mandibular molar mesialization should be considered when correcting the molar relationship using CA with intermaxillary elastics during maxillary molar distalization. It is also important to consider the anchorage teeth mesialization and undesired tipping or rotation.
II类弹力牵引与透明矫治器（CA）联合使用，对磨牙远移有效。然而，这种联合对颌间磨牙关系矫正的影响尚未得到研究。本研究旨在探讨使用II类弹力牵引与CA进行上颌磨牙远移时，上颌和下颌磨牙对总磨牙关系矫正的实际贡献率，并进一步探索临床实践中的治疗建议。
建立有限元模型（FEMs），包括第二磨牙远移（第一组），随后是第一磨牙远移（第二组）。模型A模拟通过精确切割附着的弹力牵引，而模型B模拟附着于纽扣的弹力牵引。施加100 g、150 g和200 g的力。我们记录了上颌和下颌磨牙对总磨牙关系矫正的贡献率、以0.25 mm步距的有效远移距离、倾斜和旋转角度以及牙周膜中的流体静应力。
在上颌磨牙远移过程中，下颌磨牙近移对磨牙关系矫正有显著贡献率。下颌第一磨牙近移并伴有近中舌向旋转趋势。上颌磨牙远移占据了约一半的0.25 mm步距；其余部分由支抗牙近移以及倾斜或旋转占据。当牵引力增加时，总磨牙关系矫正和有效远移增加；下颌磨牙近移贡献率也增加，旋转和倾斜趋势也增加。精确切割比纽扣具有更高的总磨牙关系矫正和更有效的远移，但下颌磨牙近移以及倾斜或旋转的贡献率也更大。
在上颌磨牙远移过程中，使用CA和颌间弹力牵引矫正磨牙关系时，应考虑下颌磨牙近移。同时，考虑支抗牙近移以及不必要的倾斜或旋转也很重要。
