Disinfection of Cariogenic Pathogens in Planktonic Lifestyle, Biofilm and Carious Dentine with Antimicrobial Photodynamic Therapy.

Antimicrobial photodynamic therapy (aPDT) has been recommended for clinical application. Its antibacterial effect on bacteria remained in dentinal tubule was seldom investigated. Here, we evaluated the antibacterial effects of aPDT on Streptococcus mutans (S. mutans) and Lactobacillus acidophilus (L. acidophilus) in planktonic lifestyle, biofilm and carious dentine. Mono-species biofilms or dentinal caries formed on human dentine slices or slabs. Bacterial suspension, biofilms and dentine caries were treated with 0.1 mg mL-1 toluidine Blue O followed by irradiation with a light emission diode (λ - 635 ± 10 nm; 500 mW; 31.5 J cm-2 ; 60 s) and 0.12% chlorhexidine (CHX), respectively. Residual bacteria were determined by microbial culture analysis and scanning electron microscopy (SEM). One-way analysis of variance (ANOVA) was performed to detect the significance of the variables. Both treatments significantly reduced the number of L. acidophilus in planktonic state, biofilm and carious dentine (P < 0.05). For S. mutans, CHX was only bactericidal against suspension (P < 0.05), while aPDT was effective on both suspension and biofilm (P < 0.05) while not for dentin caries (P > 0.05). Under the experimental conditions assessed, aPDT could be an alternative disinfection method for superficial layer of caries cavity. Its disinfection on bacteria in dentinal tubule of deep layer was deficient.