OBJECTIVE: The purposes of this study were to measure the orthodontic forces generated by thermoplastic aligners and investigate the possible influences of different activations for lingual bodily movements on orthodontic forces, and their attenuation. METHODS: Thermoplastic material of 1.0-mm in thickness was used to manufacture aligners for 0.2, 0.3, 0.4, 0.5, and 0.6 mm activations for lingual bodily movements of the maxillary central incisor. The orthodontic force in the lingual direction delivered by the thermoplastic aligners was measured using a micro-stress sensor system for the invisible orthodontic technique, and was monitored for 2 weeks. RESULTS: Orthodontic force increased with the amount of activation of the aligner in the initial measurements. The attenuation speed in the 0.6 mm group was faster than that of the other groups (p < 0.05). All aligners demonstrated rapid relaxation in the first 8 hours, which then decreased slowly and plateaued on day 4 or 5. CONCLUSIONS: The amount of activation had a substantial influence on the orthodontic force imparted by the aligners. The results suggest that the activation of lingual bodily movement of the maxillary central incisor should not exceed 0.5 mm. The initial 4 or 5 days is important with respect to orthodontic treatment incorporating an aligner.
Incisor* ; Relaxation

OBJECTIVETo measure the orthodontic forces exerted on the upper right central incisor with the increase of the distance of tooth movement and the thickness of the aligner.

METHODSThe labial movement of upper right central incisor at various distances (0.3, 0.6, 0.9, 1.2, 1.5, 1.8 mm) was designed and the stereolithography model (2 times bigger than the original model) was created with 3-D scanning and tomography output. These models were used to fabricate the aligners with different thicknesses (0.8, 1.0, 1.5 and 2.0 mm) of the thermoplastic materials (6 samples for various distances of tooth movement and thicknesses). Orthodontic forces exerted on the upper right central incisor were measured with the micro-stress sensor measurement system.

RESULTSThe orthodontic forces increased with the increase of the thickness of the aligner at the same distance of tooth movement (P < 0.05). The orthodontic force was (1.237 ± 0.082), (1.543 ± 0.059), (3.602 ± 0.102), (6.734 ± 0.063) N when the labial movement of upper right central incisor was 0.3 mm with the aligner of 0.8, 1.0, 1.5, 2.0 mm. The orthodontic forces also increased with the increase of the distance of the tooth movement at the same thickness of the aligner(P < 0.05). The orthodontic force of the aligner of 0.8 mm were (1.354 ± 0.039), (1.288 ± 0.037), (1.479 ± 0.031), (1.799 ± 0.039) N when the upper right central tooth labial movement at 0.6, 0.9, 1.2, 1.5 mm.

CONCLUSIONSThe orthodontic forces increased with the increase of the distance of tooth movement and the thickness of the aligner.

Dental Models ; Humans ; Incisor ; Orthodontic Appliance Design ; Tooth Movement Techniques