الفهرس 
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Abstract
The purpose of this study was to compare the cleaning efficacy of three Ni Ti rotary instruments: Mtwo, ProTaper Next and HyFlex CM.
Thirty single rooted extracted human teeth with single- canals, straight roots, absence of root decay and absence of previous endodontic treatment, were used in this study.
The crown of each tooth was removed at the level of the cemento- enamel junction in order to obtain root segments similar in length. Two longitudinal grooves were prepared on the palatal/lingual and buccal surfaces of each root with a diamond disc, using low speed hand piece to facilitate vertical splitting with a chisel after canal instrumentation.
Teeth were equally divided into three groups; ten teeth for each group, according to the rotary instrument used to prepare the root canal
(group A): 10 teeth will be prepared with Mtwo
(group B): 10 teeth will be prepared with ProTaper Next
(group C): 10 teeth will be prepared with HyFlex CM
Root canals were irrigated during instrumentation between each file change with 3mL of 2.5% NaOCl. After preparation 5mL of 2.5% NaOCl was used for 60s as final rinse.
The cleaning efficiency was assessed in terms of the presence of debris and/ or smear layer left on canal walls after preparation at three levels; coronal, middle and apical.
After root canals preparation, roots were divided longitudinally for SEM evaluation. Canal wall cleanliness was evaluated in three areas (coronal, middle and apical thirds of the root). Each specimen was graded from one to five according to Hulsmann et al scoring system.
The results of this investigation showed that there were no significant differences between all of the three systems; Mtwo, Protaper next and Hyflex cm, concerning cleaning efficiency. None of the three systems recorded complete cleaning of the root canal walls. In terms of debris and smear layer all of the three systems revealed that the highest score was recorded in the apical thirds of the root canals.