Determinants of Severe Orthodontic Treatment Need Using Clinically Categorized Occlusal Features

Background/Objectives: Systematic assessment of orthodontic treatment needs is essential for prioritizing care in public health programs. The Dental Aesthetic Index (DAI) provides a composite severity score; however, understanding which individual occlusal traits drive severe treatment needs has a practical screening value. This study aimed to determine which occlusal features, categorized using established clinical thresholds, independently associated with severe orthodontic treatment need. Methods: Pretreatment records of 292 patients (141 men, 151 women; aged 13-42 years) were analyzed. The outcome was severe treatment need (DAI ≥ 31). Ten DAI components were categorized using IOTN-DHC severity cutpoints; Angle and skeletal classifications were also assessed. Candidate predictors (p < 0.20) were entered into multivariate logistic regression with backward elimination. Discrimination was assessed by ROC analysis; internal validation used bootstrap resampling and cross-validation. Results: Of the 292 patients, 141 (48.3%) had severe treatment needs. Six occlusal features were independently associated with severe treatment need (all p < 0.001): overjet severity (adjusted odds ratio [OR] = 412.4; 95% confidence interval [CI]: 82.1-2072.1), missing anterior teeth (OR = 29.3; 95% CI: 8.6-99.5), open bite severity (OR = 13.4; 95% CI: 4.6-39.5), diastema (OR = 7.4; 95% CI: 2.4-22.5), molar cusp relationship (OR = 4.7; 95% CI: 2.3-9.5), and anterior spacing (OR = 2.9; 95% CI: 1.5-5.4). The area under the ROC curve was 0.971 (optimism-corrected: 0.968), and 90.8% of the patients were correctly classified by the final model (sensitivity, 89.4%; specificity, 92.1%). Angle classification, skeletal classification, sex, age, and crowding were not included in the final model. Conclusions: Six clinically categorized occlusal features assessed by visual inspection were independently associated with severe orthodontic treatment need in this explanatory analysis, with overjet severity as the dominant determinant. Categorical severity grades based on established clinical thresholds retained strong discriminative information (optimism-corrected AUC = 0.968), suggesting that simplified assessments may be sufficient for the initial screening. Dental and skeletal classifications did not provide an independent predictive value beyond that of occlusal features. External validation is needed before clinical implementation.