Development and internal validation of a nomogram integrating glycated hemoglobin and clinical parameters to predict residual periodontal pockets following non-surgical therapy

Residual periodontal pockets (RPPs) may remain after non-surgical periodontal therapy (NSPT), indicating an incomplete therapeutic response and the need for further site-specific periodontal evaluation. Elevated glycated hemoglobin (HbA1c) may impair periodontal healing, but practical tools for individualized risk estimation are limited. This study aimed to develop and internally validate a nomogram integrating baseline HbA1c with routinely available clinical parameters to predict RPP risk. This retrospective cohort study included 420 patients who underwent standardized NSPT between 2019 and 2024. The primary outcome was study-defined RPP, defined as at least one site with probing depth (PD) ≥ 5 mm at re-evaluation. Sixteen candidate predictors were evaluated using least absolute shrinkage and selection operator regression. Restricted cubic splines assessed the functional form of continuous predictors. The final logistic regression model was internally validated using 1,000 bootstrap resamples in which the complete model-development procedure was repeated. Performance was evaluated using discrimination, calibration, Brier score, and decision curve analysis. Robustness was assessed using an EFP-concordant treatment endpoint. RPPs were identified in 148 patients (35.2%). Five predictors were retained: baseline HbA1c, smoking status, Full-Mouth Plaque Score, maximum alveolar bone loss, and percentage of sites with PD ≥ 6 mm. HbA1c showed an approximately linear association with RPP risk (P for non-linearity = 0.412). The model had an apparent AUC of 0.824 and an optimism-corrected AUC of 0.810. The optimism-corrected calibration slope was 0.95, and the Brier score was 0.146. Findings remained materially consistent using the EFP-concordant endpoint. Decision curve analysis indicated potential net benefit across threshold probabilities of approximately 10%–75%. The internally validated nomogram estimates the patient-level probability of residual pocket persistence after NSPT. It may support individualized follow-up planning and patient communication but should complement, rather than replace, tooth- and site-specific periodontal re-evaluation. External validation is required before routine clinical implementation.