ABSTRACT
Since the use of rotary nickel titanium instruments is an essential part of endodontic treatment, it is important to compare the root canal cleaning ability of these instruments. The aim of this study was to compare the amount of smear layer and debris remaining following the use of four rotary instruments: MTwo, Pro Taper, Race and BioRaCe. A total of 20 mesiobuccal canals of extracted human first molars with apical root curvature of 10 to 20 were selected. Working length of all roots was 19 mm. The roots were randomly divided into four groups of 30 specimens. After the preparation of access cavity, the roots were instrumented using rotary instruments according to the manufacturer's instructions. After each file, the root canal was irrigated with 2.5%sodium hypochlorite. Then the roots were studied under scanning electron microscope. The smear layer and debris scoreswere evaluated by 2 endodontistsusingSchafer and Schlingemannclassification. Kruskal -Wallis and Dunn tests were used for statistical analysis of results. The amount of smear layer produced by MTwo was lower than the other instrumentation techniques and it was significantly lower than that in BioRaCe system [p<0.05]. The amount of debris was also lower in the mentioned group but the difference in this respect between groups was not significant. BioRaCe system had the highest level of remained smear layer while Pro Taper had the highest amount of remained debris. Within the limitations of this study, it was revealed that MTwo instruments had greater capability of removing smear layer and debris than theBioRaCe system