Antimicrobial efficacy of n-acetylcysteine, indocyanine green-activated photodynamic therapy, and 810-nm diode laser against Enterococcus faecalis: A novel in vitro study

Aim: This study aims to compare the antimicrobial efficacy of n-acetylcysteine (NAC), NAC combined with photodynamic therapy (PDT) using indocyanine green (ICG), and NAC combined with 810-nm diode laser irradiation against Enterococcus faecalis biofilms in infected root canals. Methods: Eighty-four extracted human mandibular premolars were inoculated with E. faecalis for 21 days and randomly divided into three groups (n = 28 each): Group 1, NAC irrigation; Group 2, NAC + ICG-mediated PDT activated with an 810-nm diode laser; and Group 3, NAC + 810-nm diode laser irradiation. Pre- and posttreatment bacterial samples were collected for colony-forming unit (CFU) quantification. The primary outcome was the log 10 reduction in CFU. Statistical analysis was performed using Brown–Forsythe ANOVA with Dunnett’s T3 test. Results: A total of 84 specimens were analyzed across three groups. All groups demonstrated a reduction in CFU counts following treatment, with Group II showing the greatest mean log 10 reduction (1.53 ± 0.55) compared with Group I (0.85 ± 0.29) and Group III (0.91 ± 0.12). Percentage reduction values followed a similar pattern, with Group II achieving a higher proportional decline (56.38% ±20.64%) than Group I (31.27% ±10.14%) and Group III (33.32% ±4.06%). Brown–Forsythe ANOVA indicated a significant difference among the groups (P < 0.0001). Post hoc analysis showed that Group II achieved significantly greater CFU reduction compared with both Group I and Group III, whereas no statistically meaningful difference was observed between Group I and Group III. No specimen demonstrated complete eradication (0 CFU) after treatment. Conclusion: NAC combined with ICG-mediated PDT at 810 nm produced the greatest reduction in E. faecalis biofilms and the highest eradication rate. While these findings indicate superior antimicrobial performance under controlled in vitro conditions, further studies with clinically relevant benchmarks are required before clinical translation.