A recently developed antimicrobial technique utilizing hydroxyl radicals generated by hydrogen peroxide (H2O2) photolysis represents a promising new therapy for preventing and treating dental caries. The present study compared the antimicrobial time-kill kinetics of H2O2 photolysis, conventional antiseptics, and antimicrobial photodynamic therapy (aPDT) against biofilm-forming Streptococcus mutans (cariogenic bacteria) grown on hydroxyapatite disks. H2O2 photolysis was performed by irradiating the biofilm immersed in 3% H2O2 with 365-nm light-emitting diode (LED) light at an irradiance of 1000mW/cm2 for up to 1.5min. Antiseptic treatments consisted of 0.2% chlorhexidine gluconate, 0.5% povidone-iodine, and 3% H2O2. The biofilm was immersed in each antiseptic for up to 4min. aPDT was performed by irradiating the biofilm immersed in 100μM methylene blue or toluidine blue O with 655-nm laser light at 1000mW/cm2 for up to 4min. Based on the time-kill assay, the decimal reduction value (D-value) of each treatment was determined. With a D-value of 0.06min, H2O2 photolysis exhibited the highest bactericidal effect against biofilm-forming S. mutans. In contrast, antiseptics and aPDT exerted a slower bactericidal effect, with D-values of 0.9-2.7min. In conclusion, the antimicrobial technique based on H2O2 photolysis using 365-nm LED represents a strong adjunctive chemotherapy for dental caries treatment.
Keywords: Biofilm; Chlorhexidine gluconate; Hydrogen peroxide; Hydroxyl radical; Photodynamic therapy; Streptococcus mutans.
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