Tooth-Level Radiation Dosimetry and Outcomes of Root Canal Treatment in Irradiated Patients: A Retrospective Cohort Study.

BACKGROUND: Root canal treatment (RCT) is recommended for compromised teeth in patients with radiation therapy (RT) for head and neck cancer (HNC), to minimise extraction-related osteoradionecrosis (ORN). However, literature on endodontic outcomes in irradiated patients is scarce. This retrospective clinical study aimed to investigate healing outcome, survival, and their associated prognostic factors in teeth that received non-surgical RCT in irradiated HNC patients. METHODS: Patients who underwent RT for HNC and subsequently received RCT between 2011 and 2022 were identified from electronic clinical records. Healing outcome and tooth survival were assessed from clinical and radiographic data. Radiation dose to each tooth and its periapical region was quantified by delineating these structures on RT planning CT scans. Healing was classified as healed/healing or diseased using predefined clinical and radiographic criteria. Associations between prognostic factors and healing or survival were analysed using mixed-effects logistic and Cox regression models, respectively. RESULTS: A total of 170 teeth in 82 patients were included. Among teeth reviewed at 1-4 years, 82.4% (108/131) were classified as healed/healing. Estimated survival was 85.8% (95% CI: 78.1%-94.3%) at 7 years, declining to 55.7% (95% CI: 37.4%-55.7%) at a maximum follow-up of 132 months. Pre-operative mobility significantly predicted both poorer healing (OR = 10.0; 95% CI: 1.47-68.5) and increased extraction risk (HR = 44.5; 95% CI: 6.38-310). Increasing age at RCT initiation was also associated with tooth loss (HR = 1.09 per year; 95% CI: 1.01-1.17). Radiation dose to the tooth or periapical region was not associated with healing or survival, and no cases of ORN were observed. CONCLUSIONS: Healing and survival of endodontically treated teeth in irradiated HNC patients were favourable. Pre-operative tooth mobility was associated with poorer healing and increased risk of tooth loss and should be considered during pre-radiotherapy dental assessment. In contrast, no statistically significant association was detected between radiation dose to the tooth or periapical region and healing or survival outcomes in this cohort. These findings support endodontic treatment as a means of preserving compromised teeth in irradiated jaws and reducing the risk of extraction-related ORN.