Comparison of the Discrepancy Index and the Index of Orthodontic Treatment Need

Hypothesis: We hypothesize that there is a relationship between the American Board of Orthodontics (ABO) Discrepancy Index (DI) score and the Index of Orthodontic Treatment Need (IOTN). Objective: To test whether the Discrepancy Index and Index of Orthodontic Treatment Need can be interchangeably used for determining orthodontic treatment need and case complexity. Methods: 163 de-identified records of subjects in permanent dentition were scored based off of both indices. A complete set of records included intraoral photos, OrthoCAD® digital dental models, panoramic radiograph, and cephalometric radiograph. Results: There is a statistically significant difference between DI score values for IOTN=1 subjects compared to IOTN=2-5. There is no statistically significant difference between DI score amongst IOTN groups 2-5. Conclusions: The Discrepancy Index and Index of Orthodontic Treatment Need cannot reliably be used interchangeably except in cases with very minor malocclusions. A case that is scored as IOTN=5, indicating high need for orthodontic care, will not necessarily be scored as having high case complexity as measured by the Discrepancy Index.