Abstract: [Abstract ] PURPOSE：we study the effects of the combined application of NAF and EGCG on the growth and reproduction of Streptococcus mutans there by inhibiting the occurrence and development of dental caries. Methods: The minimum inhibitory concentration (MIC) of EGCG or NAF against Streptococcus mutans was determined by microdilution method. The potential synergistic/antagonistic effects of the NaF/EGCG combination on the growth of Streptococcus mutans was determined by checkerboard microdilution assays as described previously . Cell growth was examined by OD600 nm. The fractional inhibitory concentration (FIC) was defined as the ratio of the minimum inhibitory concentration (MIC) of an agent used in combination to the MIC of the agent used alone. Results : EGCG inhibited growth of Streptococcus mutans planktonic cells at an MIC of 100ppm and NAF inhibited growth of Streptococcus mutans planktonic cells at an MIC of 500ppm. The fraction of inhibitory concentration (ΣFIC) of the NAF/EGCG combination against Streptococcus mutans was 0.375, indicating a synergistic effect of these 2 agents against Streptococcus mutans planktonic culture. Conclusions: It is shown that the combined effect of NAF and EGCG has a synergistic inhibitory effect on Streptococcus mutans planktonic cells. EGCG can cooperate with NAF to enhance the antibacterial effect of sodium fluoride, thus reducing the toxic effect of NAF , and preventing bacteria from producing fluorine-resistant properties.

Key words: Keywords: NAF, EGCG, Streptococcus mutans , Combined Antimicrobic Susceptibility Test