sem study of root canal walls cleanliness after ni-ti rotary and hand instrumentation

introduction: to compare the cleaning effectiveness of k3 and race niti rotary systems with k-flexo file instruments during the preparation of curved canals in extracted human teeth. materials and methods: a total of 50 root canals of mandibular and maxillary molars with curvatures ranging between 25º and 35 º were divided in three groups of 15 each and 5 as negative control groups. canals were prepared using a low torque control motor in two rotary groups according to manufacturer’s instructions. conventional step back with s.s k files was the preparation technique in third group. the amount of debris and smear layer was quantified on the basis of a numerical evaluation scale. the data were statistically analyzed using chi-square and likelihood ratio tests. results: in general, no significant difference in terms of amount of debris were found among three groups, only in apical zones of race and k-flexo file groups a significant difference was detected (p=0.041). race rotary system left significantly less smear layer than k-flexo file in the middle (p=0.009) and apical thirds (p=0.012), respectively. k3 significantly achieved higher scores of cleanliness than k-flexo file in apical third only (p=0.049). no significant difference between race and k3 rotary groups for residual debris and formed smear layer was detected. conclusion: obtaining higher scores of cleanliness in various regions of the canals, crown down technique and the use of rotary instrumentation seem to be superior to conventional hand instrumentation with step back technique .no significant difference between k3 with three radial lands and race with three cutting edges in terms of debris and smear layer formation was detected.