Fig. 1

Scanning electron microscopy (SEM) observation of the smear layer and Enterococcus faecalis removed after treatment in each group. Negative group: a heavy smear layer and biofilm-like structures are observed on the surface of the root canal (A–C, A: coronal region; B: middle region; C: apical region). Positive group: a few smear layer-covered areas and tubules are visible but have not completely opened and the remaining biofilm is shrunken (D–F, D: coronal region; E: middle region; F: apical region). Diode laser group: a small amount of smear layer is evidenced on the smooth root canal surface and sparse bacteria are detected (G–I, G: coronal region; H: middle region; I: apical region). Diode-NaOCl group: the smear layer is uniformly clean and the tubules are opened; there are almost no bacteria on the root canal surface (J–L, J: coronal region; K: middle region; L: apical region). Magnification: A~L-1 1000×; A~L-2 5000×