Antibacterial effects of charcoal and fluoride dentifrices in oral biofilms

Charcoal-containing dentifrices are increasingly popular for their whitening claims, but data on antimicrobial effects are limited. This study compared the antibacterial efficacy of charcoal dentifrices versus non-charcoal dentifrices containing sodium fluoride (NaF), stannous fluoride (SnF₂), or sodium monofluorophosphate (NaMFP) against multi-species oral biofilms.

Biofilms of Streptococcus mutans, S. gordonii, and S. sanguinis were grown on hydroxyapatite discs and treated for 60 s with 6 dentifrice slurries (3 charcoal, 3 non-charcoal dentifrices) or controls (saline and 0.12 % chlorhexidine, CHX). Antibacterial effects were assessed by CFU/mL; (n = 9/group) and qPCR (n = 3/group). For fluoride-type analyses, charcoal and non-charcoal dentifrices were combined (CFU n = 18/type; qPCR n = 6/type). Percent reduction was compared across groups using one-way ANOVA with post-hoc tests.

NaF dentifrices exhibited the greatest overall antibacterial activity (46.8 % reduction), followed by NaMFP (34.9 %), while SnF₂ showed minimal effect (≤ 5.7 %). Charcoal inclusion did not enhance efficacy and slightly reduced NaF activity. Species-specific responses varied: NaF eliminated S. gordonii, and significantly reduced S. mutans and S. sanguinis. Charcoal inclusion did not significantly alter species-level viability. qPCR supported CFU trends but showed limited between-group differences. Overall, fluoride type - not charcoal - primarily determined efficacy (NaF > NaMFP > SnF₂).

Fluoride type had a greater impact on antibacterial efficacy than charcoal. NaF was most effective, while SnF₂ least. Charcoal offered no benefit and may slightly diminish NaF performance. Fluoride choice is more critical than charcoal additives for caries prevention.