[Study on arch expansion effect with the clear aligner using digital registration method]

To introduce a digital registration method to compare the design effect and the actual effect of the clear aligner aided expansion in treating mild crowding, and to evaluate its clinical effectiveness.

A total of 30 patients with mild crowding who were treated by clear aligner aided expansion in Jiading District Dental Disease Prevention and Treatment Institute from January 2019 to December 2023 were selected. The anhydrite models of patients during treatment were scanned by using a D-station 3D-RI optical scanner，and the STL format data of plaster group were obtained. The STL format data of the design group were also obtained from Clincheck. The STL format data of the two groups were imported into Geomagic Studio 2012 software. The change value of arch widths and expansion rate were measured for first premolars and first molars at buccal cusps. The digital registration method was used to measure positive and negative deviation of the arch width.

The average expansion rate of maxillary first premolar, first molar, mandibular first premolar and first molar was 87.26%, 86.57%, 90.5% and 89.88% respectively. There was significant difference between the design group and the plaster group (P＜0.01). The average deviation values of maxillary buccal direction in the design group and plaster group were 0.40 mm and 0.59 mm, respectively, and those of the mandible were 0.41 mm and 0.53 mm, with significant differences between the two groups (P＜0.01). The average deviation values of the maxilla and mandible were -0.36 mm and -0.39 mm, -0.36 mm and -0.11 mm, respectively, and there was no significant difference between the two groups(P＞0.05). The buccal-lingual bias variable could be considered as a criterion for the efficacy of orthodontic treatment.

Digital registration method can be used to evaluate the effect of the clear aligner. Clear aligner aided expansion in treating mild crowding is effective. After expansion, buccal movement is difficult to control and exacerbates buccal tipping. The buccal-lingual bias variable can be considered as a criterion for the efficacy of orthodontic treatment.