Clear aligners for maxillary anterior en masse retraction: a 3D finite element study

Abstract

tang 1,2 ✉ to evaluate tooth behaviours under various maxillary incisor retraction protocols for clear aligner therapy. A three-dimensional finite element model of maxillary dentition was constructed for first premolar extraction. A loading method was developed to mimic the mode of action of clear aligners for incisor en masse retraction. Three protocols with different amounts of retraction and intrusion on incisors were designed. Initial tooth displacements and stresses on periodontal ligaments were analysed with ANSYS software. The central (U 1) and lateral (U 2) incisors exhibited uncontrolled lingual tipping and extrusion upon 0.25 mm retraction. U1 exhibited translation movement, while U 2 underwent less tipping during 0.2 mm retraction and 0.15 mm intrusion. Labial tipping and intrusion of U 1 and bodily intrusion of U 2 were observed during 0.1 mm of retraction and 0.23 mm of intrusion. With the additional intrusion on incisors, canine showed extrusion movement, and higher stresses on periodontal ligaments were shifted from U 2 to canines. Incisors also exhibited different mesial-distal angulation in the three simulations, while posterior teeth all suffered mesial inclination. Incorporating intrusion displacement in clear aligners led to a tendency of lingual root movement during incisor retraction. the complexity of tooth movement should be recognized regarding clear aligner therapy.

Effectiveness of an anterior mini-screw in achieving incisor intrusion and palatal root torque for anterior retraction with clear aligners:

“…Ironically, the magnitudes of tooth displacement in this study were on the order of micrometers (eg, 0.02 Angle Orthodontist, Vol 00, No 00, 0000 mm), which was not close to 0.25 mm (the amount of anterior retraction). However, the results were in agreement with Jones et al 14 (tooth displacements ranged from 0.012 to 0.133 mm) and with a recent finite element study on clear aligners by Jiang et al 15 This inconsistency (0.02 vs 0.25 mm) may be attributed to the fact that initial displacement tendency, and not biological displacement, was determined through FEA. For biological displacement, it would take about 2-4 weeks for alveolar remodeling to achieve the actual tooth movement (0.25 mm).…”

Three-Dimensional Finite Element Analysis on En-Mass Retraction of Maxillary Anterior Teeth With the Clear Aligner Technique

“…The ndings of the study revealed that the maxillary anterior teeth had lingual and distal tipping movements accompanied by occlusal extrusion, and the maxillary posterior teeth exhibited mesial tipping movement accompanied by an intrusion trend during the maxillary anterior teeth retraction process. The research results were consistent with clinical experience and close to those of other researchers [9,23,24] which demonstrates the rationality of this research.…”

“…The substance was de ned with a continuously homogeneous and isotropic; the orbital oor of the maxillary alveolar bone was a xed constraint. There was frictional interaction between the crown and the CA, with a friction coe cient of 0.2 [23]. Binding restrictions were found between the teeth of the PDL and the alveolar bone.…”

“…To visualize the extraction of the maxillary rst premolar, the bilateral maxillary rst premolars were deleted to simulate, and according to the scienti c literature, the root of the teeth was spread uniformly along the outer surface by 0.25 mm continuously to obtain the PDL model [10,22]. The maxillary anterior teeth were retracted bodily by 0.2 mm in sagittal direction [23], and the dentition was counted as M. Then M was imported into Geomagic Studio 12.0 software to process the space between every two teeth separately. Then the outer surface of the crown was removed as an inner surface of CA, sliced through the boundary curve of the aligner.…”

Impact of Dental Model Height on Thermoformed PET-G Aligner Thickness—An In Vitro Micro-CT Study

“…Nonetheless, it must be noted that force transmission patterns from aligners are complex and not yet fully understood [31,32]. This owes to the so called "half shell shapes" of aligners and differences in localization of contact areas to teeth and attachments.…”