Effect of shortened irrigation times with 17% ethylene diamine tetra-acetic acid on smear layer removal after rotary canal instrumentation.

The purpose of this study was to evaluate whether irrigation times of 1 minute or less with 1 mL of 17% ethylene diamine tetra-acetic acid (EDTA) effectively removed the smear layer from root canals after rotary instrumentation. Forty single-canal teeth were decoronated, instrumented, and divided into 3 experimental groups (n = 10). Ten teeth served as positive and negative controls. The experimental groups received a final rinse with 1 mL of 17% EDTA for 1 minute, 30 seconds, or 15 seconds followed by a final 3-mL rinse with 6% NaOCl. Teeth were split longitudinally and prepared for scanning electron microscopy imaging. Digital images (350x) of the approximate center of the coronal, middle, and apical sections were graded for quality of smear layer removal by 3 endodontists. Data were analyzed with nonparametric tests, with significance level set at alpha = .05. Significantly greater smear layer removal was found in the 1-minute EDTA irrigation group than the 30-second or 15-second groups.