A method to study sustained antimicrobial activity of rinse and dentifrice components on biofilm viability in vivo

To develop an improved method for quantitative assessment of antimicrobial efficacy and substantivity of mouth rinses and dentifrices on in vivo treated plaque.

Nine- and 72-h-old plaques were formed in volunteers carrying out standardized hygiene using NaF-containing dentifrice. Plaques were collected before (baseline) in vivo treatment with dentifrices or chlorhexidine mouth rinse, immediately post-treatment and after 1 or 6 h, dispersed in demineralized water and stained with live/dead stain after which bacteria were enumerated. Dispersed baseline plaques were treated with dentifrices or chlorhexidine to determine antimicrobial efficacy against planktonic bacteria.

Baseline plaques revealed 56-41% viable organisms in 9- and 72-h-old plaques, respectively. Treatment of planktonic (dispersed baseline plaque) bacteria resulted in 1-4% viable organisms. Chlorhexidine mouth rinse and dentifrices produced strong immediate antimicrobial effects, but after 1 or 6 h, the proportion of viable organisms in 9-h-old plaques rebounded significantly with only chlorhexidine mouth rinse retaining significant efficacy. Seventy-two-hour-old plaques were less susceptible to antimicrobials, although dentifrices appeared more effective after 6 h than initially, whereas efficacy of chlorhexidine rinse continued to drop with time post-treatment.

The proposed method holds promise for assessment of both immediate and retained antimicrobial actions of oral treatments against dental plaque in vivo.