Abstract: Objective: To investigate the bactericidal effect of photodynamic therapy (PDT) combined with Er: YAG laser on dental caries in rats and the acid resistance of dental hard tissue. Methods: 28 rats were randomly divided into 7 groups. The germicidal efficacy of each group was observed by spectrophotometer to determine the optical density (OD) value. The dissolution of calcium and phosphorus was detected after being soaked in 0.1 mmol/L lactic acid solution for 24 hours. The hardness of each group was tested by digital microhardness tester before and after lactic acid treatment. The tooth surface morphology, cleanliness, and dentinal tubules were observed by scanning electron microscope (SEM). Results: Compared with negative control group,the growth of bacteria of each group was significantly reduced. After lactic acid treatment, calcium and phosphorus were dissolved at different degrees, and the average microhardness of the surface was decreased. SEM observation showed that the surface of PDT combined with Er:YAG laser group was smooth and had obvious melting sealing effect on dentinal tubules. Conclusion: PDT combined with Er:YAG laser treatment of dental caries can not only kill cariogenic bacteria effectively,but also seal dentinal tubules significantly. It enhanced the acid resistance of tooth hard tissue and prevent the dental caries.

Key words: PDT, Er:YAG laser, HV Vickers-hardness, Acid resistance