Retrograde root canal retreatment with pre-bent ultrasonic files. A retrospective outcome study

Aim: To assess retrospectively the clinical and radiographic outcomes of retrograde root canal retreatment (RRR) and to identify possible prognostic factors that may affect the outcome. Methodology: Clinical records and radiographs were collected from patients who had undergone RRR between 2009 and 2016 and had a 1-year follow-up. All surgical procedures were performed by a single endodontist. The RRR technique involved minimal root-end resection and maximal length retrograde preparation using pre-bent ultrasonic files. Outcomes were categorized as complete, incomplete, uncertain or unsatisfactory healing based on clinical and radiographic findings. The complete and incomplete healing cases were pooled and considered as successes, while uncertain and unsatisfactory cases were considered failures. Prognostic factors were analysed using univariate analysis and multivariate logistic regression. Results: In total, 575 patients with 721 teeth were included. The overall success rate was 91.8%. None of the prognostic factors (including age, gender, size of periapical radiolucency and isthmus presence) had a significant influence on the outcome (P > 0.05). Univariate analysis revealed tooth type had a significant influence on outcome (P = 0.008) with mandibular incisors having a significantly lower success rate (71.4%). Multivariate analysis using logistic regression revealed that the only variable with a significant association to the outcome was retrograde preparation length (P = 0.016, odds ratio = 1.299 (1.050, 1.607), C.I. = 95%)), i.e. the longer the retrograde preparation, the better the outcome. Conclusions: Retrograde root canal retreatment was successful in 91.8% of cases. This predictable success rate was achieved while minimizing root-end resection and maximizing retrograde canal preparation length.