ABSTRACT
The smear layer is a thin layer composed of organic and inorganic debries which forms on canal walls. Removal of this layer after instrumentation is critical for adaptation between filling material, root walls and apical seal. The aim of this in vitro study was to determine the effect of 30% citric acid and 17% EDTA- 5.25% NaOCl on smear layer removal in the middle third of root canals. In this experimental study, twenty extracted anterior teeth were used. After decoronation, instrumentation was done. The teeth were divided into three groups. After final preparation the canals were irrigated by 10 ml 30% citric acid in group I and 10 ml 17% EDTA followed by 5.25% NaOCI in group 2. In control specimens, normal saline was used. Then the roots were split longitudinally and studied under scanning electron microscope. The photomicrographs were evaluated by X and Y methods. The data was analyzed by Kolmogorov-Smirnov, Leven's, Mann Whitney U and T-student tests. Canal walls were covered with smear layer in the positive control group. in both methods [X, Y], the result showed that canals irrigated with 17% EDTA- 5.25% NaOCL had less smear layer throughout the canal than group irrigated with 30% citric acid. This difference was not statistically significant in both [X, Y] methods. Both 17% EDTA-5.25% NaOCL and 30% citric acid removed the smear layer from root canal walls effectively