A model for clinical evaluation of anti-microbial effects of agents on plaque colonization.

PURPOSE: To evaluate a new improved method of microbial analysis in a cross-over clinical study by investigating the efficacy of a single application of an essential oil-containing (EOC) dentifrice as compared to its vehicle control (VC) over a 6-hr period. MATERIALS AND METHODS: Acrylic stents with retention areas for 7, 3 mm x 3 mm hydroxyapatite (HA) squares were fabricated for 12 subjects. 30 min following stent placement, one HA square was removed and sampled for viable microflora. After stent replacement, subjects were assigned either the EOC dentifrice or its VC and brushed under supervision for 1 min. Stents remained in place for the next 6 hrs. A HA square was removed at hourly intervals for 6 hrs following brushing. The microflora was analyzed for total anaerobes on Schaedler's media, for total gram-negative anaerobes on Schaedler-NV selective media, and for total Fusobacterium species on CVE selective media. Plates were incubated anaerobically at 37 degrees C for 2-5 days. Colony forming units were calculated. For each time point, pairwise t-tests were performed using the adjusted means and the pooled error term from the analysis of variance (ANOVA). RESULTS: Treatment with the EOC dentifrice resulted in a statistically reduced plaque growth. Differences were seen as reductions in: (1) total gram-negative anaerobes seen from 1-6 hrs (P < or = 0.011), (2) total anaerobic bacteria which achieved significance at 3 hrs and continued through 6 hrs (P < or = 0.005), and (3) Fusobacterium species as seen from 4-6 hrs (P < or = 0.002).