The effects of charcoal dentifrices on Streptococcus mutans biofilm development and enamel demineralization

Purpose: To evaluate the in vitro effects of commercially available charcoal dentifrices on Streptococcus mutans biofilm development and their ability to prevent enamel demineralization. Methods: Streptococcus mutans biofilm was formed on polished bovine enamel specimens (n= 9 per treatment), and treated twice-daily for 120 seconds over the course of 5 days with: charcoal dentifrice containing fluoride (1,000 ppm F) (CF+), fluoride-free charcoal dentifrice (CF-), regular fluoride (1,100 ppm F) dentifrice (F+), or regular fluoride-free dentifrice (F-). Chlorhexidine (CHX, 0.12%) and deionized water (DIW) were used as positive and negative controls, respectively. Biofilms were analyzed for bacterial viability (colony-forming units, CFU). The pH of the medium was measured daily. Enamel specimens were analyzed using Vickers microhardness (HV) and transversal microradiography (TMR). Data were analyzed using one-way ANOVA followed by post-hoc tests (a= 0.05). Results: F+ showed higher pH values than CF+ and CF-, and CF- presented higher pH than CF+, showing that CF+ did not have inhibitory effects on the acidogenicity of cariogenic biofilms. CFU was significantly decreased when specimens were treated with CF+, CF- and F+, compared to specimens treated with DIW (P≤ 0.035) or F- (P≤ 0.001), respectively. However, the reduction observed was minimal (approximately 1 log). CF+ and CF-were less effective than F+ in preventing enamel demineralization as determined using HV (P= 0.041 and P= 0.003, respectively) and TMR (P≤ 0.001). Both charcoal dentifrices (CF+, CF-) did not show relevant inhibition of S. mutans biofilm growth. Additionally, neither product prevented enamel demineralization compared to a regular fluoride-containing dentifrice.