Evaluating Photodynamic Therapy at Two Wavelengths and Cold Plasma as Alternatives to Chlorhexidine for Targeting <i>Streptococcus mutans</i>: An In-vitro Study

Background: Dental caries, driven by biofilm-forming Streptococcus mutans, remains a significant global health issue. Traditional treatments like chlorhexidine (CHX) are effective but associated with side effects, prompting interest in alternatives such as photodynamic therapy (PDT) and cold atmospheric plasma (CAP). Objectives: To compare the antibacterial efficacy of PDT at two wavelengths (810 nm and 660 nm) with different photosensitizers [indocyanine green (ICG) and methylene blue (MB)], CAP treatment, and CHX against S. mutans. Methods: An in vitro study was performed using 13 groups: CHX, PDT with or without photosensitizers, CAP (90 - 180 s), and controls. Colony-forming units (CFUs) were measured post-treatment, and data were analyzed using one-way ANOVA and Tamhane’s T2 test in SPSS26. Results: All treatments significantly reduced CFUs compared to the untreated control (mean CFUs = 2105 ± 151.10; P < 0.001). The CHX completely inhibited S. mutans (0.00 ± 0.00 CFUs; P < 0.001), followed by PDT 810 nm + ICG (23.5 ± 11.67 CFUs, P = 0.028), CAP 180 s (36.75 ± 18.87 CFUs, P = 0.030), and PDT 660 nm + MB (39.25 ± 5.62 CFUs, P = 0.001). The ICG or MB alone and laser alone showed significantly higher CFU counts (P < 0.05). Conclusions: While CHX remains highly effective, PDT and CAP can present promising alternatives with fewer side effects. Photodynamic therapy, particularly with 810 nm ICG, and extended CAP exposure could serve as adjunctive therapy for S. mutans control.