Abstract: Objective　To study the effect of methylene blue on the growth and acid production ofStreptococcus mutans, and the effect ofmethylene blue on acid productionmetabolism in plaque glycolysismodel (i-PGM)invitro, and investigate the practi- cability of methylene blue as a new kind of dental caries prevention agent.Methods　Nephelometer method was used to measure OD value ofStreptococcus mutansculture fluid in the different incubation conditions. The kinds and quantities of acid produced by Streptococcus mutansin the different incubation conditions were measured with gas chromatography. pH values of glycolysis buffer media of i-PGMin the differenttreatment conditionswere measured byORIONelectrode.Results　①The OD value ofStreptococ- cus mutanstreated by methylene blue was lower than that by normal saline, and there was significant statistical difference between them.②The kinds of acid in three different culture fluid were same, but the total quantities of acid were significantly different among three different culture fluid, in which the total quantities of acid of culture fluids treated by glucose was the greatest, and treated by methylene blue was the lest.③The pH value of i-PGMtreated by methylene blue was significantly different compared with negative control group, butwas not significantly different compared with positive control group.Conclusion　Methylene blue can inhibit the growth and acid production metabolism ofStreptococcus mutansand acid production metabolism of i-PGM.

Key words: methylene blue, Streptococcus mutans, growth, acid production, dental caries prevention