The purpose of this study was to evaluate the effects of EDTA and pulsed Nd:YAG laser on apical leakage of canal obturation. Forty-eight single-rooted teeth were used in this study. The teeth were instrumented up to a size 40 K-file and irrigated with 2.5% NaOCl between each file size. And the teeth were divided into 4 groups. In group A, the root canals were irrigated with a final flush of 5ml 2.5% NaOCl as a control group. The teeth in group B were irrigated with a final flush of 5ml 17% EDTA. The teeth in group C and D were irradiated by pulsed Nd:YAG laser(laser parameters were set at 1W, 100mJ, 10Hz, and 2W, 100mJ, 20Hz respectively).

The results were as follows:

1. Apical leakage was observed in 50% of samples in group A, 30% of samples in group B, 20% of samples in group C, and 10% of samples in group D.

2. The teeth in group B had less leakage than group A, but there was no statistically significant differences(p>0.05).

3. The teeth in group C, D had less leakage than group A, and there was statistically significant differences(p<0.05).

4. The teeth in group C, D had less leakage than group B, but there was no statistically significant differences(p>0.05).

5. There was no significant differences in apical leakage between group C and group D(p>0.05).