Abstract: Objective To study the effect of proplis on the production of lactic acid from S.Mutans.Methods S.mutans and S.sobrinus were inoculated into the TPY culture mediums which contained 5 g/L or 1.25 g/L proplis extract in water, 1.562 5 g/L proplis extract in ethanol, chlorhexidine, and TPY culture medium as control group respectively. Having been cultured for 48 h, the lactic acid in each solution was examined and compared.Results There was no statistic difference between the groups of 5 g/L proplis extract in water, 1.562 5 g/L proplis extract in ethanol, and chlorhexidine, whereas the statsitc difference between the above three groups and the control group were significant, and there was also a significant difference between the 1.25 g/L proplis extract in water group and both chlorhexidine and control group.Conclusion similar to chlorhexidine, Beijing proplis extracts in water and ethanol apparently inhibit the lactic acid production by S. mutans and S. sobrinus.

Key words: proplis, S. mutans, acid