OBJECTIVETo evaluate the effect of different concentrations of ethylenediamine tetraacetic acid (EDTA) paste on the removing root canal smear layers and the degrees of erosion on the surface of the root canal walls at the different portions of canal.

METHODSSixty human teeth with single root were instrumented using step-back technique, then were divided into six groups and treated with different concentrations EDTA paste and NaCLO solution. Group A: 0.9% saline; group B: 5.25% NaC10+5% EDTA; group C: 5.25% NaC10+10% EDTA; group D: 5.25% NaC10+15% EDTA; group E: 5.25% NaC10+17% EDTA; group F: 5.25% NaClO+20% EDTA. Then the teeth were split, the root canals with different treatments were examined with scanning electron microscope at the coronal, middle and apical thirds for smear layers removal and the degrees of erosion.

RESULTSThe effect of EDTA paste on removing smear layers at the coronal, middle thirds of the root canal increased with the concentrations. 15% EDTA paste could remove the smear layers at the coronal and middle thirds of the root canal, but the effect on apical third was invalid, and no erosion could be found in the root canal wall. 17% and 20% EDTA paste produced the erosion to the root canal wall.

CONCLUSIONThe concentrations of the EDTA paste can influence the effect of the removing smear layers, and the concentration beyond 17% would produce the erosion to root canal wall.