Using a mature biofilm model, the aim of this study was to evaluate the effectiveness of different antibacterial agents in comparison with silver diamine fluoride (SDF). Forty-eight saliva-coated enamel slabs were inoculated with Streptococcus mutans monospecies biofilm. The biofilms were then exposed to 10% sucrose in tryptone yeast-extract culture medium, 8 times per day for 7 days. After the biofilm growth period, the enamel slabs were treated with one of the following substances: 1) distilled water; 2) SDF; 3) acidulated phosphate fluoride (APF); 4) ammonium hexafluorosilicate (AHF); 5) ammonium hexafluorosilicate + cetylpyridinium chloride (AHF+CPC); or 6) 0.2% chlorhexidine (CHX). After these treatment procedures, the samples were incubated at 37ºC for 2 days, and the numbers of viable microorganisms in the biofilms were counted. The number of viable bacteria was significantly reduced by all of the antibacterial agents (P < 0.05). However, SDF showed the highest antibacterial activity (P < 0.05), and the effectiveness of the other agents was lower (P < 0.05). SDF has a highly effective antibacterial action against cariogenic Streptococcus mutans biofilm; none of the other fluoride agents used in this study, or 0.2 CHX agent, showed an antibacterial effect comparable to that of SDF. (J Oral Sci 57, 367-372, 2015)