Effect of 3D anchorage attachment on the alleviating tipping/extrusion of premolars for en-mass distalization of maxillary molars with clear aligners: A finite element study

This study aimed to explore the optimal invisible orthodontic force system during the en-mass distalization of two maxillary molars to minimize the side effect of anchorage loss by changing the direction of the application of the orthodontic force system. A high bio-fidelity 3D finite element model including maxilla, periodontal ligament, dentition, clear aligner, 3D anchorage attachment and mini-implant was established. Different lengths of lateral hooks of 3D-printed anchorage attachments and mini-implant positions into the palatal alveolus were considered. A 200 ​g distal force was applied to the lateral hooks of different horizontal lengths (3.26 ​mm, 6.52 ​mm and 9.78 ​mm) with the mini-implant as the application point. Using ABAQUS software, orthodontic tooth movements under 12 different clinical treatment designs were analyzed and calculated. The 3D anchorage attachment enhanced the anchorage of anterior teeth and alleviated the tipping/extrusion of premolars. In contrast to without clear aligners, length of the lateral hook had a negligible effect on both mesial tipping and buccal tipping with clear aligners, which could then be ignored. The change in mesial tipping was less and nearly remained constant despite of the different heights of the mini-implant. The 3D anchorage attachment assisted clear aligner can avoid the side effects of anterior tooth proclination caused by insufficient anchorage. The length of the lateral hook, and height of the mini-implant in this invisible orthodontic force system hardly affects the tooth movement of anchorage units. Clear aligners can effectively control the rotation and tipping of anchorage units caused by 3D anchorage attachment.