RT2C: Predicting Time-to-New Caries with Structured Dental Data Using RNN

Dental caries is a highly prevalent chronic condition requiring accurate tools to identify at-risk patients and guide preventive care. Most existing caries risk models provide only binary predictions and overlook time-to-event information. Considering that modern caries management relies on risk assessment during routine dental examinations, we developed RT2C, a survival model based on a recurrent neural network (RNN). This model supports caries risk management by assessing the likelihood (Caries Management by Risk Assessment [CAMBRA]) that a patient will be diagnosed with new caries by the next visit. It also estimates the time until this event occurs, using structured longitudinal dental data. Data were extracted from 4 dental organizations, comprising 466,782 patients and 1,062,553 examination visits (D0120, D0150, D0145) between 2019 and 2023. Structured electronic dental record (EDR) data included demographics, dental care history, clinical findings, and the CAMBRA-caries risk assessment (CRA). Patients were split into development (326,748 patients; 744,624 visits), validation (46,678; 106,616), and test (93,356; 211,313) sets, with similar event rates (~20%). The RT2C model used a bidirectional gated recurrent unit network to capture temporal dependencies across visits and estimate individualized survival probabilities. Model performance was compared against a Cox proportional hazards model and a random survival forest using the concordance index (C-index), integrated Brier score, and calibration analysis. Subgroup analyses evaluated generalizability across insurance types, age groups, racial groups, and CRA-based risk groups. The RT2C model achieved the highest concordance index on the held-out test set (0.883 ± 0.08), outperforming the CRA-only and traditional survival baselines. Performance remained consistent across demographic and clinical subgroups, demonstrating robustness and fairness across diverse populations. RT2C models visit-indexed risk trajectories and predicted new caries occurrence by the subsequent visit, aligning with the preventive framework of CAMBRA. By integrating longitudinal EDR data, it adds value to existing CRA tools and supports proactive, personalized caries management.