title: Changes in force associated with the amount of aligner activation and lingual bodily movement of the maxillary central incisor.
abstract: 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.
authors.affiliation: Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing, China.
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing, China.
authors.forename: Chaochao
authors.initials: C
authors.lastname: Ren
authors.affiliation: Institute of Microelectronics, Tsinghua University, Beijing, China.
authors.forename: Zheyao
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Institute of Microelectronics, Tsinghua University, Beijing, China.
authors.forename: Pai
authors.initials: P
authors.lastname: Zhao
authors.affiliation: Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing, China.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing, China.
authors.forename: Yuxing
authors.initials: Y
authors.lastname: Bai
keywords: Activation amount; Aligners; Orthodontic force; Orthodontic treatment