Lethal photosensitization of cariogenic bacteria inseminated into tooth slices

Objectives: Photodynamic therapy (PDT) is an eradication of target cells by reactive oxygen species produced by means of a photosensitizing compound and light of an appropriate wavelength. The main aim of this study was to investigate the sensitivity of different cariogenic bacteria to lethal photosensitization in the tooth structure itself. Methods: Tooth slices from extracted human molar teeth of adult patients were sterilized by autoclaving and then incubated with broth cultures of 4 different cariogenic organisms for 24h at 37^oC to allow the formation of biofilms. Photosensitization was carried out with a diode (GaAlAs) laser in the presence of Toluidine Blue O (TBO) as the sensitizer. The bacterial biofilms were exposed to the diode laser and photosensitizer for 1minute. Control groups were exposed to TBO alone and laser alone. Results: Overall, the results showed reductions in the viability of all bacteria tested. Significant reductions were observed in the viability of Lactobacillus casei (L. casei) (87% killing) as well as Streptococcus mutans (S. mutans) (81% killing) and Actinomyces viscosus (A. viscosus) (47% killing). Interestingly, the viability of S. salivarius was the least affected (14% killing). Conclusions: The results of the current study indicate that the most sensitive organism was L. casei, followed by S. mutans, A. viscosus, and S. salivarius.