SnF₂-containing toothpaste effect on enamel demineralization and S. mutans biofilm

Objectives: Stannous fluoride (SnF₂) containing toothpaste has anticaries and antigingivitis effects but the impact of its antimicrobial activity on the caries process is not well understood. The aim of this study was to evaluate the effect of SnF₂-based toothpaste on biofilm formation and on enamel demineralization, using a Streptococcus mutans (SM) biofilm caries model.
Methods: SM UA159 were cultured for 144 h on saliva coated enamel specimens (n=20) with known surface hardness (SH) and maintained suspended in a 24-well culture plate. Developed biofilms were exposed 3x/day to 10% sucrose for 5 min and treated 2x/day for 1 min with one of the following treatments: deionized water (negative control), chlorhexidine (CHX) gluconate 0.12% (positive control), or slurries of commercial fluoride toothpastes, either a SnF₂-based or a NaF-based. The culture medium was changed 2x/day and the pH monitored as an indicator of biofilm acidogenicity. At the end of the incubation, biofilms were analyzed by confocal laser scanning microscopy for live/dead bacteria and 3D structure. Biomass, thickness and % viability were calculated. Enamel surface hardness was assessed and percentage of loss (%SHL) was calculated as an indicator of demineralization.
Results: %SHL (mean±SD;n=20) was 40.9±12.4^A; 4.9±3.7^B; 6.9±5.3^B; 15.8±5.9^C for negative control, CHX, SnF₂ and NaF groups, respectively (groups with different letters were statistically different, p<0.05). The biofilm of the groups treated with SnF₂ and CHX presented approximately 70% less biomass and thickness than negative control and NaF groups. The NaF group did not show an antimicrobial effect. After incubation for 72 h, the culture medium pH was around 5.0 for the NaF and negative control groups, 5.5 for the SnF₂, and 7.1 for the CHX group. .
Conclusions: The results of the study suggest that the antimicrobial activity observed using this model for the SnF₂-containing toothpaste could explain its greater reduction of enamel demineralization.