To explore the reproducibility of tooth width measurements in digital models from different stages of Invisalign^? treatment, and provide evidence for evaluation of the achieved amount of interproximal reduction (IPR) .

Fifty nonextraction patients were treated with Invisalign^? without interproximal reduction. Digital models of each patient were acquired using the iTero intraoral scanner and examined using ClinCheck software twice: at the start of the case (T1) and during the first midcourse correction or refinement (T2) . The individual tooth width and the anterior and overall Bolton ratios were recorded from ClinCheck. The upper and lower combined anterior and overall teeth widths (UATW, UOTW, LATW and LOTW respectively) were calculated. The reproducibility was determined using intraclass correlation coefficients (ICCs) . The differences between T1 and T2 were used to assess the precision of tooth width. The cases were further divided into groups according to tooth arrangement, age and sex, and the precision of combined teeth width measurements among groups were compared.

The individual tooth width, combined teeth widths and Bolton ratios had ICCs≥0.917. For individual tooth width, the mean differences between T1 and T2 were-0.09-0.03 mm, and the standard deviations were 0.06-0.17 mm. For combined teeth widths, the mean differences were-0.14-0.10 mm, and the standard deviations were 0.21-0.53 mm. The difference in anterior ratio was (0.02 ± 0.71) % and in overall ratio was (0.25 ± 0.61) %. The precision of LOTW showed significant difference among the Spacing, Non-crowding and crowding groups (P<0.05) , while the precision of UATW, UOTW and LATW showed no significant difference (P>0.05) . The precision of all four combined teeth widths measurements showed no significant difference between female and male groups (P>0.05) or between adolescent and adult groups (P>0.05) .

The individual tooth width and combined teeth widths measurements of the digital models from different stages of Invisalign^? treatment showed high reproducibility and clinically acceptable precision in ClinCheck. However, the precision had a relatively large individual variability. The precision of combined teeth widths were not influenced by age and sex but by tooth arrangement to some extent. The tooth width measurements could be generally used as reference for treatment plan and evaluation of the achieved IPR amount.