Objective To evaluate the ability of Biopure MTAD in removing smear layer in vitro. Methods Forty extracted single-rooted human teeth were randomly divided into five groups：Distilled water in group A, 5.25% NaClO and 17% EDTA in group B, 1.3% NaClO in group C, 1.3% NaClO and Biopure MTAD in group D, 1.3% NaClO and 3% EDTA in group E. The canals were prepared and irrigated with one of the five different irrigating agent respectively. The amount of smear layer and erosion on the surface of the root canal walls were examined with scanning electron microscope. Results The whole surfaces of root canals in group A and C were covered by smear layer. The surfaces of root canals in the coronal and middle thirds of samples in group B, D, E were free of smear layer（P＞0.05） and the apical third of canals in the group D were significantly cleaner（P＜0.05） than that in group B and E. The coronal and middle sections were significantly eroded in group B compared with group D and E（P＜0.05）. The degree of erosion in the apical section was not statistically different among group B, D and E （P＞0.05）. Conclusion Biopure MTAD and 1.3% NaClO are effective irrigating agents for removal of the smear layer on the surface of root canal. There is no significant change in the structure of the surface of root canal.
