Factors associated with the outcome of root canal treatment—A cohort study conducted in a private practice

Aim To investigate the association of various pre‐, intra‐ and post‐operative factors on root canal treatment outcome. Methodology In this cohort study, primary or secondary root canal treatment of mature permanent teeth was performed by a single endodontist in a private practice over 13 years, and followed 1–4 years after treatment. Treatment details and clinical and radiographic data were collected. The proportion of successfully treated teeth and roots based on strict radiographic (periapical index (PAI) ≤2) and clinical criteria (absence of pain, swelling or sinus tract) was estimated. To evaluate joint associations of prognostic factors and treatment success probability, 44 pre, intra‐ and post‐operative factors were investigated using bivariate associations, and a multiple logistic regression model was fitted using Generalized Estimating Equations. Results 1259 teeth (2445 roots, 3149 canals) were assessed with a recall rate of 91%. The proportion of successfully treated teeth was 79.9% [95% confidence interval 77.7–82.1]. Eleven prognostic factors were identified that significantly reduced the odds ratio (OR) for treatment success at tooth level. Six were preoperative: injury history (OR = 0.05[0.01–0.24]), root PAI (OR = 0.29[0.20–0.42], 0.21[0.13–0.34] and 0.22[0.12–0.42] for PAI = 3, 4 and 5, respectively, against PAI = 1), lesion diameter (OR = 0.30[0.21–0.43] and 0.24[0.16–0.37] for diameters of 1‐5 mm and ≥6 mm, respectively, against no lesion), tooth type (OR = 0.51[0.27–0.97] and OR = 0.45[0.24–0.83] for premolars and molars, respectively, against incisors or canines), tenderness to periapical palpation (OR = 0.64[0.43–0.94]) and two canals per root (OR = 0.67[0.54–0.83]). Four factors were intraoperative: root filling of unsatisfactory quality (OR = 0.18[0.08–0.40]) or extending beyond or shorter than 2 mm from the apex (OR = 0.44[0.26–0.75] and 0.62[0.40–0.97] respectively), resin sealer (OR = 0.58[0.39–0.87] against bioceramic sealer) and single visit treatment (OR = 0.40[0.21–0.75] against multiple visits). One factor was post‐operative: defective coronal restoration (OR = 0.35[0.21–0.56]). Conclusion The following factors were associated with unsuccessful root canal treatment: (i) history of injury, apical periodontitis with increased severity (larger lesion, higher PAI, tenderness to periapical palpation), or complicated anatomic conditions (premolar or molar, two canals in a single root); (ii) technically suboptimal root filling (of u