Smear layer reduction in root canals prepared with triangular and rectangular files as evaluated by scanning electron microscopy

Objective: Root canal preparation procedures can produce a smear layer when in contact with the root canal wall, which can result in treatment failure. As such, the cross-section shape of the file may influence the production of smear layer. In this study, we compared the smear layer production at the apical third of the root canal wall between files with a triangular or rectangular cross-section shape. Methods: Thirty-two human premolar samples taken from mandibles were divided into two groups whose root canals were prepared using files with either a triangular (One Curve®, n=16) or rectangular (Hyflex EDM®, n=16) cross-section shape. After preparation, the root canals were irrigated with a combination of 2.5% NaOCl and 17% ethylenediaminetetraacetic acid (EDTA). The smear layers in the apical third of the root canal walls were observed using a scanning electron microscope and quantified according to the Foschi scoring system. Results: The Mann–Whitney U-test revealed a significant difference between root canal preparations using the different file shapes. The group prepared with the triangular file produced lower smear layer scores compared with the group prepared with the rectangular file. Conclusion: Root canal preparations using files with different cross-section shapes (e.g., triangular and rectangular), followed by irrigation with 2.5% NaOCl and 17% EDTA, produced smear layers in the apical third area. However, root canal preparations using files with a triangular cross-section shape were shown to reduce smear layer production compared with files with a rectangular cross-section shape.