Korean J Orthod.  2016 Mar;46(2):65-72. 10.4041/kjod.2016.46.2.65.

Changes in force associated with the amount of aligner activation and lingual bodily movement of the maxillary central incisor

• Li X
• Ren C
• Wang Z
• Zhao P
• Wang H
• Bai Y

• KMID: 2159353
• DOI: http://doi.org/10.4041/kjod.2016.46.2.65

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.

Keyword

Aligners; Orthodontic treatment; Orthodontic force; Activation amount

MeSH Terms

Incisor*
Relaxation

Figure

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  Figure 1 Production process for the thermoplastic aligners. A, OrthoDS_D software ver. 4.4 (Wuxi Angel Align Biotech nology Co., Ltd., Wuxi, China) was used to design different activation ranges for the lingual bodily movement of the maxillary right central incisor on a model twice the size of the digitized maxillary standard model. B, The resin models. C, The aligners.

• 

  Figure 2 The orthodontic force generated by the thermoplastic aligners was measured using a micro-stress sensor measurement system for invisible orthodontic techniques. A, The micro-stress sensor measurement system. B, The standard resin model with invisible aligner and the sensor chip bonded on the tooth surface and connected with flexible cables. C, A photograph of the stress sensor.

• 

  Figure 3 Orthodontic force relaxation curves for the five sets of lingual movement aligners.

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  Figure 4 Mean forces of the thermoplastic aligners, with standard deviations. A, There were no statistically significant differences between day 4 and any of the subsequent days as determined by Bonferroni's test (p > 0.05) in the 0.2 mm group. B, There were no statistically significant differences between day 4 and any of the subsequent days as determined by Bonferroni's test (p > 0.05) in the 0.3 mm group. C, There were no statistically significant differences between day 5 and any of the subsequent days except days 10 and 14, as determined by Bonferroni's test (p > 0.05) in the 0.4 mm group. D, There were no statistically significant differences between day 5 and any of the subsequent days as determined by Bonferroni's test (p > 0.05) in the 0.5 mm group. E, There were no statistically significant differences between day 4 and the subsequent days as determined by Bonferroni's test (p > 0.05) in the 0.6 mm group. *p < 0.05, **p < 0.01; Bonferroni's test.

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