Antimicrobial effect of gaseous and aqueous ozone on caries pathogen microorganisms grown in biofilms.

Purpose: To evaluate the anti-microbial effect of gaseous and aqueous ozone on biofilms of caries pathogen microorganisms with regard to concentration and time dependency.

Methods: Biofilm cultures of Actinomyces naeslundii, Streptococcus mutans and Lactobacillus paracasei were grown on nitro-cellulose-membranes for 48 hours. The membranes were cut into equal-sized pieces and exposed to chlorhexidine digluconate (CHX) (positive control; 0.1-20%), gaseous (1-64 g m3) and aqueous ozone (1.25-20 microg ml(-1)) for 60 seconds. The influence of exposure time (30-120 seconds) was tested for exemplary concentrations of the three agents. Colony forming units of bacteria were counted. The bacteria survival rate was given as percentage of the negative control (PBS for CHX/aqueous ozone, ambient air for gaseous ozone).

Results: There was no difference in bacterial reduction of different species with general reduction close to zero for high concentrations of all agents. Univariate ANOVA with partial eta-squared (Eta2) statistics showed major effects for concentration/contact time of the agent on bacteria survival. High concentrated gaseous and aqueous ozone seem to be potential alternatives to CHX with equivalent antimicrobial activity.