Tooth survival following pulpectomy in primary molars with apical periodontitis and preoperative factors associated with failure: a retrospective cohort study

Long-term survival data for pulpectomy in primary molars with apical periodontitis (AP) remain limited. This retrospective cohort study aimed to evaluate the tooth survival following pulpectomy in primary molars with AP and to identify factors associated with failure. Dental records of healthy children aged 3–6 years who underwent pulpectomy in at least one primary molar between 2019 and 2021 at Mahidol University were reviewed. Teeth were included when preoperative radiographs showed findings consistent with apical periodontitis. Failure was defined as the presence of clinical symptoms or radiographic progression involving displacement of the succedaneous tooth bud. Tooth survival was estimated using the Kaplan–Meier method, and restricted mean survival time (RMST) was calculated using a 48-month truncation time. Factors associated with failure were analysed using multivariable Cox proportional hazards regression with robust cluster variance estimation. Sensitivity analysis was performed using an inverse probability of censoring weighting-adjusted Fine–Gray model to account for documented competing events and potential informative censoring. A total of 326 primary molars from 242 children were included. Over the observation period, 47 molars (14.4%) failed. The Kaplan–Meier estimated survival probability was 100% at 12 months, 95.4% at 24 months, and 52.02% at 48 months. The RMST at 48 months was 42.77 months. In the primary multivariable Cox model, older age at treatment (HR 1.05, 95% CI 1.01–1.09), preoperative sinus tract (HR 4.98, 95% CI 1.99–12.45), and root resorption involving one-third to two-thirds of the root length (HR 2.96, 95% CI 1.01–8.69) were associated with higher failure hazard. Sensitivity analysis supported the robustness of the association with preoperative sinus tract, whereas the association with age was attenuated and the association with advanced root resorption was less stable. Treatment-level variables, including visit regimen, irrigant type, obturation material, obturation quality, and operator training level, were not associated with failure. Within the limitations of this retrospective single-centre study and the adapted retention-focused outcome framework, pulpectomy in primary molars with AP showed a 48-month Kaplan–Meier survival probability of 52.02% and an RMST of 42.77 months. Preoperative sinus tract showed the most consistent prognostic association with failure, while age remained directionally consistent but less precise, and advanced root resorption should be interpreted cautiously. These prognostic findings should be considered hypothesis-generating and warrant confirmation in larger prospective cohorts.