scanning electron microscopic evaluation of residual smear layer following preparation of curved root canals using hand instrumentation or two engine-driven systems

introduction: in this experimental study, the amount of smear layer (sl) remnants in curved root canals after chemomechanical instrumentation with two engine-driven systems or hand instrumentation was evaluated. methods and materials: forty-eight mesiobuccal roots of mandibular first molars with curvatures ranging between 25 and 35 degrees (according to schneider’s method) were divided into three groups ( n =16) which were prepared by either the protaper universal file series, reciproc single file system or hand instrumentation. the canals were intermittently irrigated with 5.25% naocl and 17% (ethylenediaminetetraacetic acid) edta, followed by distilled water as the final rinse. the roots were split longitudinally and the apical third of the specimens were evaluated under 2500× magnification with a scanning electron microscope (sem). the mean scores of the sl were calculated and analyzed using the non-parametric kruskal-wallis and mann-whitney u tests. results: the mean scores of the sl were 2.00±0.73, 1.94±0.68 and 1.44±0.63 µm for the protaper universal, reciproc and hand instrumentation, respectively. mean score of sl was significantly less in the hand instrumentation group than the protaper ( p =0.027) and reciproc ( p =0.035) groups. the difference between the two engine-driven systems, however, was not significant ( p =0.803). conclusion: the amount of smear layer in the apical third of curved root canals prepared with both engine-driven systems was similar and greater than the hand instrumentation technique. complete cleanliness was not attained.