Objective: Historically, the Incisor Irregularity Index (II) has been utilized to investigate the stability of orthodontic treatment. Recently, other occlusal indices have been developed, but it is uncertain how these different indices agree with one another. Therefore, the purpose of this study was to investigate the correlation of three occlusal indices - the Peer Assessment Rating (PAR), the American Board of Orthodontics - Objective Grading System (ABO) and the II - at the pre-treatment, post-treatment, and post-retention periods. Methods: The sample was selected from the post-retention records of the University of Washington Department of Orthodontics, and was based on the presence of radiographs and models at pre-treatment (T1), post-treatment (T2), and post-retention (T3). The T3 PAR index was measured for all subjects who met the inclusion criteria (n=547). Two groups were selected based on the T3 PAR scores – a stable group (n=50, PAR <3) and an unstable group (n=44, PAR>10). For these 94 subjects, the PAR and II were measured at T1, T2, and T3, and the ABO was measured at T2 and T3. Pearson correlation coefficients were calculated for each of the indices at each time period. Results: The PAR-II correlations were 0.55 at T1, 0.38 at T2, and 0.76 at T3. The PAR-ABO correlations were 0.48 at T2 and 0.74 at T3. The ABO-II correlations were 0.12 at T2 and 0.46 at T3. Conclusion: The PAR-II and PAR-ABO correlations were moderate, with II and ABO scores tending to increase as PAR scores increased. The ABO-II correlations were the weakest, especially at T2. The low correlations indicate that these indices provide different information, and therefore, it may be difficult to generalize treatment difficulty or success based on the scores from the different indices. This study was supported by the University of Washington Dental Alumni Association.

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