Canine distal movement impact on teeth and aligner deformation in clear aligner treatment: A 3D finite element study

Although the use of clear aligners (CAs) has gained popularity in orthodontics, it faces challenges in extraction cases, particularly the "roller coaster effect" (mesial molar movement, distal canine tipping, and lingual incisor tipping/extrusion). Previous finite element studies focused on CAs as force-applying agents, neglecting counterforces from teeth to CAs. This study aimed to analyze how canine distal movement patterns affect incisors via tooth-aligner force interactions.

A three-dimensional finite element model was developed, including teeth, periodontal ligament, attachments, and CAs, based on cone-beam computed tomography and intraoral scanning data. Three groups simulated different canine distal movement modes: Group 1 (bodily movement with vertical rectangular attachments), Group 2 (bodily movement with paired optimized attachments), and Group 3 (distal tipping with vertical rectangular attachments). Multi-step iterative modeling methods were used to simulate long-term treatment, analyzing tooth displacements, contact stresses, and CA deformations.

All groups demonstrated distal tipping of canines with the rotation center at the apical third, despite bodily movements in Groups 1 and 2. Group 2 exhibited significant canine rotation (3.36°). Incisors revealed unintended displacements: Groups 1 and 2 demonstrated higher lingual cervical pressure from CAs, causing greater buccal displacement (0.30-0.39 mm) and rotation (1.30-1.74°) compared to Group 3 (0.14-0.23 mm, 0.59-1.01°). Group 3 revealed better CA adaptation and reduced incisor movement due to minimized counterforces from actively tipped canines.

As current attachments cannot achieve bodily canine distalization, tipping is inevitable. Designed bodily movements induce CA deformation and incisor lingual tipping/extrusion, while active distal tipping reduces adverse effects. Orthodontists should avoid programming unattainable bodily canine movements in premolar extraction cases and prioritize tipping-based strategies with subsequent root control.