Assessing Post-Orthodontic Change Using Two Occlusal Indices

Objectives: To assess post-orthodontic change using the Discrepancy Index (DI) and Little's Irregularity Index. Methods: Twenty-three patients had dental casts fabricated at the end of their orthodontic treatment (T1). Dental casts were remade 30 days later for each patient (T2). Retainers were not used during this month. The 46 post-treatment dental casts were coded, measured, and scored by a calibrated operator using each index. Intra-rater reliability tests were conducted for all 46 casts. Changes from T1 to T2 were noted using the DI and Little's Irregularity Index. Absolute changes as well as the direction of change (favorable versus unfavorable post-orthodontic tooth movement) were recorded. Agreement between indices were noted. Results: Intra-rater reliability tests demonstrated no significant differences between Irregularity Index scoring sessions (p < 0.05). No statistical analysis was necessary to establish intra-rater reliability in the DI as no differences were found between the two DI scoring sessions. Little's Irregularity Index, designed purely to measure lower incisor irregularity, detected a change in all twenty-three sets of casts, while the Discrepancy Index detected a change in 7 sets of casts (30.4%). When all DI categories were considered (excluding cephalometrics), the DI detected a change in 15 sets of casts (65.2%). Both Little's Irregularity Index and the Discrepancy Index detected that some cases actually experienced a decrease in crowding after one month without retainers. Conclusion: Little's Irregularity Index demonstrated a greater ability to detect post-orthodontic change in the lower anterior region. Thus, the Irregularity Index may be the index of choice when assessing post-orthodontic treatment outcomes and studying post-orthodontic changes with regard to the mandibular anterior region. However, the more comprehensive method to assess post orthodontic change may involve a combination of the DI and Little's Irregularity Index.