Development and internal validation of a clinical risk index for predicting progression of mandibular anterior crowding in the mixed dentition: a prospective longitudinal cohort study

Background To develop and internally validate a clinically applicable risk-prediction model for estimating the progression of mandibular anterior crowding in mixed dentition.Materials and methods This prospective longitudinal study included 450 children aged 7–9 years, followed by approximately four years. Mandibular anterior crowding progression was defined as an increase of ≥2 mm in the Little’s Irregularity Index. Twelve dental, cephalometric, and soft tissue variables were evaluated. Penalized logistic regression (LASSO) was used for model development, and a simplified clinical scoring system was derived. Model performance was assessed using discrimination, calibration, and internal bootstrap validations.Results Crowding progression was observed in 36% of the participants. Six predictors are retained in the final model. The model demonstrated a good discriminative ability (AUC = 0.87) and satisfactory calibration. The derived scoring system showed a reliable diagnostic performance with minimal optimism after internal validation.Conclusion Mandibular anterior crowding progression is influenced by a combination of spatial, dentofacial, and soft tissue factors. The proposed scoring system provides a practical tool for early risk stratification; however, external validation is required before its routine clinical application.