In vitro effect of fluoride-free mouthwashes on Streptococcus mutans biofilm

To evaluate the efficacy of commercially available, fluoride-free mouthwashes sold in Indianapolis, IN, on Streptococcus mutans biofilm.

Eighty-one different mouthwashes were purchased. A 16-h culture of S. mutans UA159 was treated with the mouthwashes in three dilutions (1:3, 1:6, and 1:12), prepared in Tryptic Soy broth supplemented with 1% sucrose. The minimum inhibitory concentrations (MIC), planktonic, and biofilm growth were evaluated using a spectrophotometer. In addition, the growth for minimum bactericidal concentration (MBC) was evaluated using five μL of the dilution and incubated on blood agar. For the analysis of the results, the mouthwashes were separated into six groups according to their active ingredients (cetylpyridinium chloride/CPC, n = 25; essential oils/EO n = 10; whitening/W (hydrogen peroxide/ sodium hexametaphosphate), n = 12; Natural-Derived Actives / NDA, n = 15; zinc chloride/ZC, n = 3; others/O, n = 16). ANOVA followed by the Tukey test was performed (p < 0.05).

Regarding MIC, planktonic, and biofilm growth of S. mutans, there was a significant decrease for the W and CPC groups (p < 0.001). The EO and W groups had more inhibition on S. mutans biofilm compared to the CPC group (p < 0.05). For ZC, NDA, and O groups, there were different effects within the same group, presenting a large variability. About MBC, W and CPC groups presented the higher inhibition (W > CPC > EO > NDA/ZC/O).

The mouthwashes demonstrated significant effect on S. mutans biofilm, especially in the 1:3 dilution. W and CPC groups had a more significant effect on S. mutans biofilm.

S. mutans is an important bacterium in dental caries and periodontal diseases. Our study showed that non-fluoridated mouthwashes affect the initial stages of biofilm formation.