Relative activity of dentifrice ingredients against dental plaque biofilms

Aim: To evaluate the antibacterial effects of formulations of triclosan (0.3% w/v), stannous fluoride (0.45% w/v) and stannous fluoride combined with zinc lactate at 0.45% w/v and 2.5% w/v, respectively (SZ) on the microbial ecology of oral biofilms. Methods: Dental plaque biofilms were cultured using modified drip flow reactors (MDFRs) where artificial saliva was passed over hydroxyapatite-coated slides to sustain a salivary inoculum taken from replicated single donor volunteers. Antibacterials were applied 4 x daily for 20min over 6 days. Plaque mass was determined gravimetrically. Differential culture was used to quantify the numbers of total aerobes and facultative species, total anaerobes, Gram-negative anaerobes and streptococci. Ecological profiles were characterized using PCR-DGGE of 16sRNA genes. Results: TCS was significantly more effective than SZ at reducing total biomass following multiple treatment periods (>95% at 6d). No significant effect on total biomass was apparent for SF alone. Culture showed TCS to be the most effective agent with significant (P<0.05) reductions of all three bacterial groups. SF was the least effective, causing only minor, transient reductions in the streptococci. Addition of zinc to stannous fluoride, SZ significantly enhanced the antibacterial effects compared to SF alone. The PCR-DGGE analysis, whilst not quantitative, confirmed that eubacterial diversity was reduced by TCS and SZ, but not by SF alone. The in-vitro biofilm communities broadly reproduced their salivary inocula. Sequence analysis revealed a diverse, predominantly facultative microbiota. Conclusions: The antibacterial efficacy of triclosan (TCS) is higher than that of both stannous fluoride (SF) and the combination of stannous fluoride with zinc lactate (SZ). The addition of zinc contributes significantly to the antibacterial efficacy of the stannous fluoride/zinc lactate (SZ) combination.