['The purpose of this ex\xa0vivo study was to evaluate the percentage reduction of accumulated hard tissue debris (AHTD) in the mesial root canal system of mandibular molars under different final irrigation regimens by means of micro-computed tomographic imaging.', "Sixty curved mesial roots of mandibular molars with 2 independent canals joint apically by an isthmus (Vertucci type II) were selected. Specimens were scanned at a resolution of 12.5\xa0μm, anatomically matched, and distributed into 3 groups (n\xa0=\xa020) according to the preparation protocol: Self-Adjusting File (SAF; ReDent Nova, Ra'anana, Israel), Reciproc (VDW GmbH, Munich, Germany), and Revo-S (Micro-Mega, Besançon, France) systems. Then, each group was subdivided into 2 subgroups (n\xa0=\xa010) according to the final irrigation protocol with the SAF or EndoVac system (Discus Dental, Culver City, CA). The percentage volume and percentage reduction of AHTD after root canal preparation and final irrigation protocols were statistically compared using 1-way analysis of variance, the paired sample and the independent Student's t tests. The level of significance was set at 5%.", 'Within groups, the mean percentage volume was significantly reduced after the final irrigation procedures in either the SAF (from 1.52%-1.78% to 1.01%-1.20%) or EndoVac (from 2.11%-2.23% to 1.31%-1.52%) subgroups (P\xa0<\xa0.05). In the experimental groups, the mean percentage reduction of AHTD ranged from 29.15%-39.90% after the irrigation protocols, with no statistical difference between groups (P\xa0>\xa0.05).'] Does supplementary step for Removing Hard Tissue Debris from Isthmus-containing Canal Systems?