The reduction of pathogenic microorganisms in supragingival plaque is one of the principal factors in caries prevention
and control. A large number of microorganisms have been reported to be inactivated in vitro by photodynamic therapy
(PDT). The purpose of this study was to develop a rat model to investigate the effects of PDT on bacterial reduction in
induced dental caries. Twenty four rats were orally inoculated with Streptococcus mutans cells (ATCC 25175) for three
consecutive days. The animals were fed with a cariogenic diet and water with 10% of sucrose ad libitum, during all
experimental period. Caries lesion formation was confirmed by Optical Coherence Tomography (OCT) 5 days after the
beginning of the experiment. Then, the animals were randomly divided into two groups: Control Group: twelve animals
were untreated by either light or photosensitizer; and PDT Group: twelve animals were treated with 100μM of methylene
blue for 5min and irradiated by a Light Emitting Diode (LED) at λ = 640±30nm, fluence of 172J/cm2, output power of
240mW, and exposure time of 3min. Microbiological samples were collected before, immediately after, 3, 7 and 10 days
after treatment and the number of total microaerophiles was counted. OCT images showed areas of enamel
demineralization on rat molars. Microbiological analysis showed a significant bacterial reduction after PDT.
Furthermore, the number of total microaerophiles in PDT group remained lower than control group until 10 days posttreatment.
These findings suggest that PDT could be an alternative approach to reduce bacteria in dental caries.