Risk factors associated with vertical root fracture following root canal treatment: a retrospective cohort study

Vertical root fracture (VRF) is an important cause of failure after root canal treatment (RCT), yet the relative contributions of systemic, anatomical, procedural, and restorative factors remain incompletely characterized. This study aimed to identify factors associated with VRF after RCT using a retrospective cohort framework with a nested matched case-control analysis. Consecutive RCT-treated teeth from June 2021 to June 2025 were retrospectively evaluated. VRF was ascertained using a composite reference standard incorporating clinical, periapical radiographic, cone-beam computed tomography, and direct surgical or extraction findings when available. Each VRF tooth was matched to two non-VRF controls by sex, jaw, tooth type, age, and RCT completion date. Associations with VRF were examined using conditional logistic regression with patient-level clustered robust variance estimation. Among 528 eligible teeth, 86 developed VRF, corresponding to an event proportion of 16.3%. The matched sample comprised 86 VRF teeth and 172 controls. The primary multivariable model included 226 teeth from 80 informative matched sets. Diabetes mellitus was associated with higher odds of VRF (adjusted odds ratio [aOR], 2.91; 95% confidence interval [CI], 1.30–6.50; P = 0.009), as were extensive coronal tissue loss (aOR, 1.98; 95% CI, 1.10–3.56; P = 0.023), over-instrumentation (aOR, 4.84; 95% CI, 1.37–17.12; P = 0.014), and longer time to definitive restoration per 30 days (aOR, 1.36; 95% CI, 1.16–1.59; P < 0.001). Greater remaining dentinal wall thickness was associated with lower odds of VRF per 0.1-mm increase (aOR, 0.83; 95% CI, 0.74–0.94; P = 0.004). Findings were directionally consistent across sensitivity and multiple-imputation analyses. VRF after RCT was associated with patient-, tooth-, procedure-, and restoration-related factors. Diabetes mellitus, extensive coronal tissue loss, over-instrumentation, and delayed definitive restoration were associated with higher VRF odds, whereas greater remaining dentinal wall thickness was associated with lower odds.