PDF(Pubmed)
Abstract：
BACKGROUND: Mesial tipping of posterior teeth occurs frequently during space closure with clear aligners (CAs). In this study, we proposed a new modification of CA by localized thickening of the aligner to form the enhanced structure and investigate its biomechanical effect during anterior retraction.
METHODS: Two methods were employed in this study. First, a finite element (FE) model was constructed, which included alveolar bone, the first premolars extracted maxillary dentition, periodontal ligaments (PDL), attachments and aligners. The second method involved an experimental model-a measuring device using multi-axis transducers and vacuum thermoforming aligners. Two groups were formed: (1) The control group used common CAs and (2) the enhanced structure group used partially thickened CAs.
RESULTS: FE model revealed that the enhanced structure improved the biomechanics during anterior retraction. Specifically, the second premolar, which had a smaller PDL area, experienced a smaller protraction force and moment, making it less likely to tip mesially. In the same vein, the molars could resist movement due to their larger PDL area even though they were applied larger forces. The resultant force of the posterior tooth was closer to the center of resistance, reducing the tipping moment. The canine was applied a larger retraction force and moment, resulting in sufficient retraction of anterior teeth. The experimental model demonstrated a similar trend in force variation as the FE model.
CONCLUSIONS: Enhanced structure allowed force distribution more in accordance with optimal principles of biomechanics during the extraction space closure while permitting less mesial tipping and anchorage loss of posterior teeth and better retraction of anterior teeth. Thus, enhanced structure alleviated the roller coaster effect associated with extraction cases and offered a new possibility for anchorage reinforcement in clear aligner therapy.
METHODS: Two methods were employed in this study. First, a finite element (FE) model was constructed, which included alveolar bone, the first premolars extracted maxillary dentition, periodontal ligaments (PDL), attachments and aligners. The second method involved an experimental model-a measuring device using multi-axis transducers and vacuum thermoforming aligners. Two groups were formed: (1) The control group used common CAs and (2) the enhanced structure group used partially thickened CAs.
RESULTS: FE model revealed that the enhanced structure improved the biomechanics during anterior retraction. Specifically, the second premolar, which had a smaller PDL area, experienced a smaller protraction force and moment, making it less likely to tip mesially. In the same vein, the molars could resist movement due to their larger PDL area even though they were applied larger forces. The resultant force of the posterior tooth was closer to the center of resistance, reducing the tipping moment. The canine was applied a larger retraction force and moment, resulting in sufficient retraction of anterior teeth. The experimental model demonstrated a similar trend in force variation as the FE model.
CONCLUSIONS: Enhanced structure allowed force distribution more in accordance with optimal principles of biomechanics during the extraction space closure while permitting less mesial tipping and anchorage loss of posterior teeth and better retraction of anterior teeth. Thus, enhanced structure alleviated the roller coaster effect associated with extraction cases and offered a new possibility for anchorage reinforcement in clear aligner therapy.
摘要：
背景：在使用清晰矫正器（CA）的空间闭合期间，后牙的内翻经常发生。在这项研究中,我们提出了一种新的CA修饰方法,通过局部增厚矫正器形成增强结构,并研究其在前缩过程中的生物力学作用.
方法：本研究采用两种方法。首先,建立了有限元(FE)模型，其中包括牙槽骨，第一次拔除上颌牙列的前磨牙，牙周韧带（PDL），附件和对齐器。第二种方法涉及实验模型-使用多轴换能器和真空热成型对准器的测量装置。形成两组：（1）对照组使用普通CA，（2）增强结构组使用部分增厚的CA。
结果：FE模型显示，增强结构改善了前回缩过程中的生物力学。具体来说,第二个前磨牙，PDL面积较小，经历了较小的牵引力和力矩，使它不太可能给小费。同样，即使施加了较大的力，磨牙也可以由于其较大的PDL面积而抵抗运动。后牙的合力更接近阻力中心，减少翻倒的时刻。犬被施加了较大的收缩力和力矩，导致前牙充分缩回。实验模型显示了与FE模型相似的力变化趋势。
结论：在拔牙间隙闭合过程中，增强的结构允许力分布更符合生物力学的最佳原理，同时允许后牙的内侧倾翻和锚固损失减少，前牙的回缩更好。因此，增强的结构减轻了与拔除病例相关的过山车效应，并为明确对准治疗中的锚固加固提供了新的可能性。
方法：本研究采用两种方法。首先,建立了有限元(FE)模型，其中包括牙槽骨，第一次拔除上颌牙列的前磨牙，牙周韧带（PDL），附件和对齐器。第二种方法涉及实验模型-使用多轴换能器和真空热成型对准器的测量装置。形成两组：（1）对照组使用普通CA，（2）增强结构组使用部分增厚的CA。
结果：FE模型显示，增强结构改善了前回缩过程中的生物力学。具体来说,第二个前磨牙，PDL面积较小，经历了较小的牵引力和力矩，使它不太可能给小费。同样，即使施加了较大的力，磨牙也可以由于其较大的PDL面积而抵抗运动。后牙的合力更接近阻力中心，减少翻倒的时刻。犬被施加了较大的收缩力和力矩，导致前牙充分缩回。实验模型显示了与FE模型相似的力变化趋势。
结论：在拔牙间隙闭合过程中，增强的结构允许力分布更符合生物力学的最佳原理，同时允许后牙的内侧倾翻和锚固损失减少，前牙的回缩更好。因此，增强的结构减轻了与拔除病例相关的过山车效应，并为明确对准治疗中的锚固加固提供了新的可能性。
