Oval-shaped canal retreatment with self-adjusting file: a micro-computed tomography study

The aim of this study was to assess the efficacy of removing the filling material from oval-shaped canals with rotary retreatment files, with or without the additional use of self-adjusting file (SAF), using micro-computed tomography. Oval-shaped canals from 20 maxillary premolars were prepared and assigned to two groups (n = 10), according to the obturation technique: cold lateral condensation (CLC) or vertical condensation (VC). Then, retreatment procedure was performed with retreatment rotary instruments followed by SAF. The specimens were scanned after each procedure and the volume of the filling material calculated. Median and interquartile range (IQR) percentages of the remaining filling material after each retreatment technique were statistically compared by Wilcoxon and Mann-Whitney U tests with a significance level of 5 %. The median percentage volume of the filling residue after rotary retreatment procedure was 1.59 (IQR = 1.26) and 0.42 (IQR = 0.86) in the CLC and VC groups, respectively (p < 0.05). After the use of SAF, the median percentage was 1.26 (IQR = 0.75) and 0.12 (IQR = 0.53) in the CLC and VC groups, respectively (p < 0.05). Statistically significant difference was also observed within the group after the additional use of SAF (p < 0.05). None of the retreatment procedures completely removed the filling material. The additional use of the SAF improved the removal of filling material after the retreatment procedure with rotary instruments. Filling material left after retreatment procedure may harbour necrotic tissue and bacteria, which could lead to a persistent disease and reinfection of the root canal system. The additional use of self-adjusting file after the conventional retreatment procedures may improve root canal cleanliness, allowing a better action of the irrigating solution.