Abstract: Abstract Objective: To study the role of photodynamic therapy using hematoporphyrin monomethyl ether as photosensitizer in the prevention of dental caries by establishing the caries rat model. Methods: Wistar rats, whose molars were inoculated with Streptococcus mutans (S. mutans), were fed with caries - inducing diet 2000# in order to establish the caries rat model. These rats were divided into five groups, whose molars were treated respectively with 10 ng/L HMME-PDT (group A), 20 ng/L HMME-PDT (group B), 40 ng/L HMME-PDT (group C), 0.2 g/L sodium fluoride as positive controls (group D), and with 0.9％sterile physiological saline as negative controls (group E) once a week for four weeks and recorded the changes of S. mutans every week. The rats were then killed. The surface morphology of dental caries of the rats was observed by scanning electron microscope. Results: The colony count in each group shows no significant difference in the first and second weeks ( P<0.05). The colony counts of group B and C are significantly reduced compared with group E in the third week ( P<0.05). In the fourth week the colony counts of group A、B and C are significantly reduced compared with group E (P<0.05 or P<0.01 ). Meanwhile the colony count of group C is significantly lower than both group A and B (P<0.05). The tooth enamel of both group C and D are found to be damaged most slightly, and the tooth surfaces of the two groups are relatively smooth. Conclusion: PDT has anticaries effect in vivo. PDT is thought to be a promising method in the prevention of caries.

Key words: HMME, PDT, streptococcus mutans, caries morphology