Sawsan, TabbaaAlshahrani, sami2025-10-052025https://hdl.handle.net/20.500.14154/76541Introduction: The American Board of Orthodontics (ABO) Discrepancy Index (DI) is widely used to assess the complexity of orthodontic cases. However, its scoring system assigns significant weight to skeletal parameters such as ANB and SN-MP angles—components that are often unmodifiable in adult patients receiving non-surgical treatment. This raises concerns about whether the DI accurately reflects true treatment complexity and outcomes in adult orthodontic care. This study aimed to evaluate changes in DI scores before and after comprehensive orthodontic treatment in adult patients. It also investigated the influence of gender, premolar extraction status, and treatment duration on DI score reduction. Methods: A total of 102 adult patients (≥18 years) treated at Jacksonville University were included. Pre- and post-treatment DI scores were assessed using ABO scoring criteria. Statistical analyses included paired t-tests, independent t-tests, ANOVA, and Pearson correlation. Results: The mean DI score decreased significantly from 19.39 ± 15.97 to 5.59 ± 7.60 (p < 0.001). Patients treated with premolar extractions showed greater DI reductions than those without (18.24 vs. 10.21 points; p = 0.002). No significant gender-based differences were observed. A weak inverse correlation was found between treatment duration and DI change (r = –0.209, p = 0.035). Conclusions: Orthodontic treatment in adults leads to a significant reduction in DI scores. However, the persistent influence of unchanging skeletal components highlights limitations in the current DI model. These findings support the need for potential modification of the DI—such as soft-capping skeletal weights—in adult orthodontic evaluations to ensure accurate reflection of treatment complexity and outcome.27en-USAmerican Board of Orthodontics (ABO) Discrepancy Index (DI)Thesis