This study confirms the findings of previous in vitro and in vivo studies which demonstrated the essential oil mouthrinse to have significant biocidal activity against oral micro-organisms. These studies all support the primacy of a bactericidal mechanism in producing the plaque and gingivitis reductions observed in numerous clinical trials conducted on the essential oil mouthrinse.

Elevated proportions of Candida albicans in biofilms formed on dentures are associated with stomatitis whereas Streptococcus mutans accumulation on restorative materials can cause secondary caries. Candida albicans, S. mutans, saliva-derived and C. albicans/saliva-derived mixed biofilms were grown on different materials including acrylic denture, porcelain, hydroxyapatite (HA), and polystyrene. The resulting biomass was analysed by three-dimensional image quantification and assessment of colony-forming units. The efficacy of biofilm treatment with a dissolved denture cleansing tablet (Polident(®)) was also evaluated by colony counting. Biofilms formed on HA exhibited the most striking differences in biomass accumulation: biofilms comprising salivary bacteria accrued the highest total biomass whereas C. albicans biofilm formation was greatly reduced on the HA surface compared with other materials, including the acrylic denture surface. These results substantiate clinical findings that acrylic dentures can comprise a reservoir for C. albicans, which renders patients more susceptible to C. albicans infections and stomatitis. Additionally, treatment efficacy of the same type of biofilms varied significantly depending on the surface. Although single-species biofilms formed on polystyrene surfaces exhibited the highest susceptibility to the treatment, the most surviving cells were recovered from HA surfaces for all types of biofilms tested. This study demonstrates that the nature of a surface influences biofilm characteristics including biomass accumulation and susceptibility to antimicrobial treatments. Such treatments should therefore be evaluated on the surfaces colonized by the target pathogen(s).

The data indicate that maintaining good oral health for denture wearers requires daily use of a denture cleanser rather than an alternating regimen. The inability of the denture cleanser to sterilize during intermittent treatments demonstrates the difficulty in controlling established biofilm. Moreover, the presence of mature biofilm may result in high levels of inflammation, but this can be controlled through denture cleansing.

Although laboratory studies are not necessarily predictive of clinical activity; they can help to elucidate mechanisms underlying clinical activity when the latter has been established. In a recent clinical study, an essential oil mouthrinse (Listerine Antiseptic) was shown to be significantly more effective than an amine fluoride/stannous fluoride mouthrinse (Meridol) in inhibiting supragingival plaque formation. This paper reports the results of laboratory studies comparing the antimicrobial effectiveness of these 2 mouthrinses using a kill kinetics assay and a plaque biofilm kill assay. In both assays, the essential oil mouthrinse was considerably more effective than the amine fluoride/stannous fluoride mouthrinse. These findings are consistent with the results of the clinical trial and may help to explain the observed differences in clinical activity.