Discrepancy index, treatment complexity index and objective Grading system: correlation between parameters, indices and implications for treatment

An assessment of orthodontic treatment duration and results allows for measurable outcomes, goal-setting, and the establishment of patient management standards. It is important information that can be utilised for educational purposes in an orthodontic postgraduate program. The aim of this study was to determine correlations of the parameters within and between the Objective Grading System (OGS), Discrepancy Index (DI) and Treatment Complexity Index (TCI) and identify those factors associated with treatment outcomes and duration. This retrospective cohort study involved a consecutive sampling of 242 pre- and post-treatment patient records from the postgraduate orthodontic clinic between 2013 and 2017. The cases were assessed using the DI, OGS, and TCI pre-treatment. Treatment outcomes were assessed using the OGS. Spearman’s Rank Correlation Coefficients were computed within and between the indices. Multiple and logistic regressions were used to evaluate associations between treatment outcomes and duration, respectively. Within DI, significant correlations (p < 0.05) were observed between overjet-overbite, overjet-occlusal relationship, overjet-crowding, overbite-anterior open bite, overbite-crowding, anterior open bite-lateral open bite, anterior open bite-crowding, lingual posterior cross bite-crowding. Within pre-OGS, significant correlations (p < 0.05) were observed between alignment-marginal ridge, alignment-occlusal relationship, alignment-root angulation, overjet-interproximal contact, marginal ridge-buccolingual inclination, marginal ridge-overjet, marginal ridge-occlusal contact, marginal ridge-occlusal relationship, overjet-occlusal contact, overjet-occlusal relationship, overjet-root angulation, occlusal relationship-root angulation, interproximal contact-root angulation. Within TCI, functional appliance correlated with orthognathic surgery (p < 0.001), rapid palatal expansion (RPE) (p = 0.005) and multidisciplinary collaboration (p = 0.001). Pre-OGS correlated with DI (p < 0.001) and TCI (p = 0.026). Cephalometric (p = 0.002) and other conditions (p = 0.031) were associated with treatment outcomes. RPE was associated with extended treatment duration (p = 0.014). DI, OGS, and TCI exhibited weak correlations within and between indices. Cephalometric values, clinical conditions, and RPE use should be carefully considered during treatment planning.