To explore the factors influencing the failure of root canal treatment in apical periodontitis, and to construct and validate a nomogram prediction model for the efficacy of root canal treatment in apical periodontitis based on these factors.

A prospective study was conducted involving 150 patients with apical periodontitis treated at Huizhou First People's Hospital from April 2024 to June 2025. All patients underwent root canal treatment and were followed up for 6 months. They were divided into the treatment failure group and the treatment success group according to the efficacy criteria of root canal treatment. Clinical data of the patients were collected. Logistic regression analysis was used to identify the factors influencing the failure of root canal treatment in apical periodontitis. A nomogram prediction model for the failure of root canal treatment in apical periodontitis was constructed, and the performance of this risk prediction model was validated.

The follow-up results showed that among the 150 patients with apical periodontitis, 35 (23.33%) had treatment failure and 115 (76.67%) had treatment success. Logistic regression analysis revealed that tooth position (posterior teeth), the number of root canal treatments (≥2 times), crown sealing effect (crown leakage), root canal filling length (underfilling/overfilling), and instrument fracture (present) were independent risk factors for the failure of root canal treatment in apical periodontitis, with odds ratios (ORs) of 2.002, 2.079, 2.255, 2.063, and 1.950, respectively. The corresponding 95% confidence intervals (CIs) were 1.080-3.711, 1.159-3.729, 1.111-4.575, 1.076-3.954, and 1.113-3.416, with P-values of 0.028, 0.014, 0.025, 0.030, and 0.020, respectively. The nomogram model developed using these five risk factors demonstrated an area under the ROC curve (AUC) of 0.836 (95% CI: 0.781-0.892), indicating good discrimination. The slope of the calibration curve was close to 1, and the Hosmer and Lemeshow test showed that the model had good fit (χ² = 7.568, P = 0.268) .

Tooth position, the number of root canal treatments, crown sealing effect, root canal filling length, and instrument fracture are risk factors affecting root canal treatment in apical periodontitis. The nomogram model constructed based on these factors has good accuracy and clinical application value, and may serve as a reference for clinical treatment of apical periodontitis.