Estimating arch length discrepancy through Little's Irregularity Index for epidemiological use

The objective of this study was to evaluate the diagnostic capability of Little's Irregularity Index (LII) in order to estimate the arch length discrepancy (ALD) in a dental arch. Dental casts with a full permanent dentition, excluding third molars, from 200 12- to-16-year-old schoolchildren from a representative high school located in Lima, Peru, were used. Incisal irregularity was measured using the LII, whereas ALD was calculated as the difference between available and required space in each dental arch anterior to the first permanent molars. The receiver-operator characteristic (ROC) curve was used to contrast the LII with three different dichotomized ALDs and locate optimized cut-off points. Correlation between ALD and LII was -0.68 (P < 0.001). According to ROC curves, LIIs of 2.45, 4.00, and 4.55 mm were the optimized cut-off points to estimate negative ALDs higher than 0, 3, and 6 mm, respectively. LII's highest diagnostic capability was found for estimating negative ALD greater than 3 mm with a sensibility of 0.78 and a specificity of 0.76. Based on the present findings, LII could potentially be used in epidemiological surveys as a valid and less time-consuming measurement of crowding compared with ALD; however, further studies are needed to test the reliability of this approach in field settings.