Evaluation of commonly used occlusal indices in determining orthodontic treatment need

The main objective of this study was to validate commonly used occlusal indices in measuring treatment need, irrespective of their original objective: Index of Orthodontic Treatment Need (IOTN) that includes a dental health component (DHC) and an aesthetic component (AC), Peer Assessment Rating (PAR) index, Index of Complexity, Outcome, and Need (ICON), Discrepancy Index (DI), and Facial Aesthetic Index (FAI).

The dental casts, x-rays, and photographs of 101 participants were randomly selected among patients whose orthodontic treatment was completed. The indices were validated against the panel assessments of four experts using the receiver operating characteristic curve analysis. The area under the curve (AUC) helped to determine their optimal cut-off points.

The raters exhibited an excellent level of inter-rater reliability in assessing need scores [intra-class correlation coefficients (ICC) = 0.85]. The DHC, AC, ICON, and PAR demonstrated 'good' diagnostic properties (AUC = 0.85, 0.84, 0.83, and 0.82, respectively). Adding the AC and the DHC into a combined index score [our proposed Combined Index of Orthodontic Treatment Need (CIOTN)] yielded the strongest correlation with need (r = 0.79) and the highest AUC value of 88 per cent with 91 per cent sensitivity and 71 per cent specificity. The DI had poor discriminating abilities (AUC = 0.69), however, its dental component was substantially better (AUC = 0.81). The supplemental FAI did not enhance the correlation of indices with need.

The DHC, AC, ICON, PAR, and only the dental component of the DI reliably captured treatment need. The newly combined CIOTN had superior diagnostic properties than its components and all other indices, probably because of the cumulative values of its components. The FAI could not be validated as a supplemental measure of treatment need.