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 unsatisfactory quality or not ending within 2 mm of radiographic apex) performed in a single-visit, or use of resin sealer instead of novel bioceramic sealer; (iii) suboptimal quality coronal restoration.