Correlation between the Crowding Severity, the Amount of IPR and the Number of Teeth Moved

The aim of this study is to determine the relationship between the severity of crowding, the need of the interproximal enamel reduction (IPR, stripping), and the number of moved teeth. One hundred and twenty-seven patients aged from 18 to 62 years, of whom 99 (78%) women and 28 (22%) men in need of active orthodontic treatment were included in the study. All patients underwent orthodontic treatment with DENT@LIGN digital aligners on etsablished protocol. The severity of crowding and the amount of IPR were measured. The stripping is coded in six groups, based on amount (≤ 1 mm; 1.1 to 2.0 mm; 2.1 to 3.0 mm; 3.1 to 4.0 mm; 4.1 to 5.0 mm, and greater than 5.1), and the crowding in four groups: no crowding; mild crowding (0.1 mm to 3.0 mm); moderate crowding (3.1 mm to 7.0 mm); severe crowding (over 7.1 mm). The Spearman test showed a significant positive correlation between stripping size and crowding severity in both jaws. In the upper jaw the correlation coefficient is rs = 0.430, p < 0.001. In the lower jaw, the correlation coefficient was higher rs = 0.514), p <0.001. The results of the Pearson test showed a direct proportional relationship between the number of teeth in need of movement and the size of stripping in the upper and lower jaws. Based on the number of moved teeth, the size of the stripping can be predicted by the following formulas: Upper jaw stripping (mm) = –0.3891 + 0.1711 × Number of moved teeth, with predictive value of R-square = 17.2%; Lower jaw stripping (mm) = –0.8965 + 0.2773 × Number of teeth moved, with predictive value of R-square = 28.1%.