Photoinhibition of Streptococcus mutans Biofilm-Induced Caries Progression in Human Dentin by Violet-Blue Light

Objectives: The purpose of this in-vitro study was to determine the effectiveness of violet-blue light on preventing the progression of dental caries produced by Streptococcus mutans biofilm on human dentin specimens.
Methods: S. mutans UA159 biofilm was formed on human dentin specimens (4×4×2 mm³) in a 96-well microtiter plate and was incubated for 13 h in 5% CO₂ at 37°C in the presence of Tryptic Soy Broth (TSB) or TSB supplemented with 1% sucrose (TSBS). Violet-blue light from Quantitative Light-Induced Fluorescence (QLF) with a peak wavelength of 405 nm was used to irradiate the biofilm. Before irradiation, supernatant liquid was removed, and the biofilm was treated continuously with QLF for 5 min. Treatment was done twice-daily with an interval of 6 h for 5 days except with one treatment on the final day. Colony forming units (CFU) of the treated biofilm, changes in fluorescence (ΔF; QLF-Digital Biluminator^TM), lesion depth (L) and integrated mineral loss (ΔZ; both transverse microradiography) were quantified at the end of the 5^th day of treatment.
Results: In the violet-blue light irradiated groups there was a significant reduction (p<0.05) of bacterial viability (CFU) of S. mutans with TSB and TSBS. Violet-blue light irradiation resulted in reduction of ΔF and L of dentinal surface with TSBS.
Conclusions: These results indicate that violet-blue light can serve as a treatment for reducing the numbers of S. mutans cells, thereby potentially reducing biofilm formation and caries formation.