Abstract: PURPOSE: To investigate the scavenging effect of diode laser combined with 5.25% sodium hypochlorite (NaClO) and 17% metal chelated ethylenediaminetetraacetic acid (EDTA) on Enterococcus faecalis (E.faecalis) in the root canal. METHODS: From January 2023 to December 2023, totally 82 single permanent teeth were freshly extracted from the outpatient clinic of the Department of Stomatology of Ningde Hospital affiliated to Ningde Normal University, and the tartar and periodontal ligament were removed with ultrasound instruments and periodontal curettage, and the root canal model with E.faecalis infection was established after disinfection. Scanning electron microscopy (SEM) was used to observe whether the root canal model of E.faecalis infected lateral branch was successfully established. A total of 80 E.faecalis-infected lateral root canal models were successfully prepared and randomly divided into 4 groups with 20 in each group. Group A was treated with diode laser, group B was treated with 17% EDTA+5.25% NaClO solution, group C was treated with 17% EDTA+5.25% NaClO+ diode laser, and group D was treated with 0.9% NaCl solution. The difference in the number of colonies between the groups before and after treatment was compared, the sterilization rate was calculated, and the treatment situation of each group was observed under SEM. Results: After 4 weeks of inoculation, a complete E.faecalis biofilm was formed on the root canal wall of isolated teeth, which closely adhered to and penetrated into the dentinal tubule, and the E.faecalis infection model was successfully constructed. After treatment, the number of colonies in the 4 groups was significantly lower than that before treatment(P<0.05). Group C had the lowest number of colonies and the highest bactericidal rate after treatment, while group D had the opposite effect, and the difference was statistically significant (P<0.05). There was no significant difference in the number of colonies, bacterial reduction and sterilization rate between group A and group B (P>0.05). After treatment, the root canal walls of group A and B had smear layers and sparse E.faecalis. The dentin tubules were open but rough, and the openings of some tubules were closed. In group C, the small tube openings were completely exposed, the wall surface was smooth and free of impurities, the small tube openings were molten and the diameter decreased. In group D, E. faecalis was linearly and chainly distributed. The root canal walls were covered by the smear layer, and the small canal openings were difficult to be seen. CONCLUSIONS: Semiconductor laser in combination with 5.25% NaClO and 17% EDTA have a good bactericidal effect on the lateral root canals on the infected side of E. faecalis and can be used as a supplement to traditional root canal disinfection.

Key words: Lateral root canal, Enterococcus faecalis, Diode laser, Sodium hypochlorite, Metal-chelated ethylenediaminetetraacetic acid