Fig. 3

Representative SEM images showing morphology of dentin surface after treatment at different frequencies. a Control group b acid etching group, arrow indicates open dentin tubule, c 5 Hz laser group, arrow indicates protruding out of the peritubular dentin, d 10 Hz laser group, arrows indicate fish-scale and lamellar dentin, e 15 Hz laser group, arrow indicates periodontal dentin cracks, f 20 Hz laser group, arrows indicate periodontal dentin deep cracks, g 25 Hz laser group, arrow indicates the disappearance of the fish-scale and lamellar morphology and the boundaries between and around the tubes are unclear, h 30 Hz laser, arrow indicates the collapsed tissues between the dentin tubes, coking, or carbonization