Orthodontic Trend Assessment of Four Decades using DI and ABOGS

Objective: To compare pre-treatment case complexity and treatment outcomes using the Discrepancy Index (DI) and American Board of Orthodontics Grading System (ABOGS) respectively. Materials and Methods: Corresponding pre- and post- treatment dental casts were assessed using DI and ABOGS to evaluate case complexity and quality of outcomes, from a sample drawn from 1960-2005. Information gathered included, but was not limited to, duration of treatment, mandibular canine and first molar width, and extractions. A total of 655 randomly selected cases (148 from 1960's, 194 from 1970's, 215 from 1980's, and 98 from 2000's) were evaluated by a single, self-calibrated operator. Results: Reliability tests (intraclass correlations) revealed good reliability with values of 0.987(DI) and 0.781(ABOGS). Individually, the evaluating scores showed statistical significance as a total (p=0.00) and between 1960's, 1970's, and 1980's compared to the 2000's (p=0.00). DI had mean scores of 14.36 ± 5.98, 14.56 ± 7.98, 12.39 ±7.06, 9.714 ± 5.82, respectively to the progressing decades. Variables of significance included overjet (p=0.00), overbite (p=0.003), and occlusion (p=0.002). ABOGS had means of 14.59 ± 7.53, 17.65 ± 8.56, 14.64 ± 6.69, 8.586 ± 5.92, respectively, to consecutive decades. Almost all variables within the ABOGS showed statistical significance (p<0.005) expect Bucco-lingual (BL) inclination. Discussion: Orthodontic post-treatment results illustrated an improvement between the decades with the 2000's having the lowest scores indicating the best results. A similar decrease in pre-treatment scores suggested that cases were less complex over the decades studied. For ABOGS, BL inclination was not significant possibly suggesting that occlusal relationship and occlusal contacts are more representative of occlusal correction. Conclusions: A directly proportional improvement in DI and ABOGS throughout the decades indicated that a more functional outcome was achieved with less complex cases.