Objectives: Two studies were conducted to determine the antimicrobial effect of rinsing with an essential oil-containing mouth rinse 12 h after a single rinse and 12 h after 2 weeks of twice daily rinsing, during the daytime and overnight.
Materials and methods: These studies utilized a randomized, double-blind, controlled crossover design. Following baseline sampling of bacteria from supragingival plaque and the dorsum of the tongue, subjects began twice-daily rinsing with either an essential oil mouth rinse containing 0.09% zinc chloride (Tartar Control Listerine Antiseptic) or a negative control rinse. Bacterial sampling was repeated 12 h after the first rinse, and again 12 h after the final rinse 14 days later. The sampling schedule was adjusted according to whether the study was investigating daytime or overnight activity. Samples were plated on Schaedlers medium (total anaerobes), Schaedlers Nalidixic/Vancomycin medium (Gram-negative anaerobes), and OOPS medium (volatile sulphur compound (VSC)-producing organisms). Inter-group log10 transformed colony-forming units/ml counts from samples of supragingival plaque and tongue swabs on each of the three media were compared by analysis of covariance.
Results: The mean bacterial counts in subjects using the essential oil mouth rinse were significantly lower (p< or =0.005) than mean counts in subjects using the control rinse in all the comparisons, i.e., tongue and supragingival plaque samples on each of three media at two sampling periods in the daytime and overnight study, respectively. Mean bacterial count percent reductions for plaque samples ranged from 56.3 to 95.3; percent reductions for tongue samples ranged from 61.1 to 96.1. There was a trend to higher reductions after 14 days' rinsing than after the initial rinse.
Conclusion: Rinsing with the essential oil mouth rinse can have long-lasting effects in reducing anaerobic bacteria overall as well as Gram-negative anaerobes and VSC-producing bacteria. The significant reductions in numbers of these bacteria produced by the essential oil mouth rinse, both in plaque and on the dorsum of the tongue, can play a key role in explaining the essential oil mouth rinse's effectiveness in reducing supragingival plaque and gingivitis as well as its effectiveness in controlling intrinsic oral malodor over prolonged periods.