Endodontic retreatment of curved canals using Reciproc, Hyflex CM and Prodesign Duo Hybrid Systems

The aim of this ex vivo study was to evaluate the efficacy of the Reciproc, Hyflex CM, and ProDesign Duo Hybrid in the retreatment of mesial root canals with Vertucci Type 4 of mandibular molars with curvatures between 10 and 20 degrees. Forty-five mesial roots of mandibular molars were prepared up to size 25.06 Nickel-Titanium (NiTi) file and filled by the single cone technique. The roots were then divided into 3 groups according to retreatment procedures: Reciproc R25 followed by R40; Hyflex 25.04 followed by 40.04; ProDesign Duo Hybrid 25.06 followed by 40.05. The canals were irrigated with 1 mL 1% sodium hypochlorite, and a final rinse was performed with 5 mL 17% EDTA for 3 minutes. Microcomputed tomography scans were performed in each step of the procedure to evaluate root canal transportation at distances of 2, 4, 6, 8 and 10 mm from the apex and volume of endodontic filling remaining at segments of 1-3, 3-5, and 5-7 mm from the apex. The filling material that was not removed during retreatment was evaluated by confocal laser scanning and the percentage after each procedure was expressed in terms of percentage of the initial root-filling material volume. The time taken to remove the material and re-instrumentation was measured in seconds with a digital chronometer. Statistical analysis was performed with t-paired, ANOVA, Kruskal-Wallis and Friedman tests (p < 0.05). In all groups, sections at 4, 6, 8, and 10 mm from the apex were transported to the danger zone, towards the furcation. However, the section at 2 mm from the apex was transported in opposite direction to the furcation, but no statistically significant differences (p > 0.05) in canal transportation and filling material removal were found between the 3 groups. Filling removal and re-instrumentation took significantly (p < 0.05) less time in the Reciproc group. None of the retreatment techniques completely removed the root fillings. The results suggest that no difference exists between the groups in apical transportation of curved canals. The Reciproc system took less time for filling removal and re-instrumentation and the combination of reciprocating and rotary files in the retreatment of curved canals was as efficient as rotary and reciprocating motion.