Methods: A total of 75 single canal tooth with minimum curve were selected and divided into three groups of 25. Canals were prepared with NiTi hand. flexmaster or FKG race instruments using crown down preparation technique, up to size 30. After splitting the roots longitudinally, the amount of debris and smear layer were quantified on the basis of Hulsmann method using a scanning electron microscope. The data were analyzed using SPSS statistical soft ware (Kruskal wallis test).
Results: Completely cleaned root canals were not found with any of the three instruments. Flex master instruments left debris with smaller size in middle and coronal thirds of canal but not the apical third. Flexmaster instruments left less smear layer Just in apical third of canal significantly.
Conclusion: No completely cleaned root canals were found with any of the three instruments Flexmaster instruments revealed better canal cleaning in all three third of root canal significantly. Flexmaster instruments left less smear layer in apical third of canal significant.