Objectives: To compare the in vivo antibacterial activity of a 0.2% chlorhexidine (CHX) mouthrinse on salivary flora and on de novo plaque.

Methods: The study group was formed of 10 healthy volunteers. A special acrylic appliance was designed, with 3 inserted glass disks on each buccal side, allowing for biofilm growth. The volunteers wore the appliance during 48 hours and then performed a 0.2% CHX mouthrinse (Oraldine Perio, Pzifer, Barcelona, Spain) for 1 minute. Simultaneously, saliva samples were taken and diskes were removed at 30 seconds and 1, 3, 5 and 7 hours after the CHX mouthrinsing. A epifluorescence technique (BacLightTM LIVE/DEAD stain) imaged by confocal microcopy was used to evaluate bacterial vitality on saliva and plaque samples. Counting of live/dead bacteria was carried out in 20 microscopy fields in each saliva sample. Optical sections of 1 &mum were made throughout the biofilm under the confocal laser scanning microscope in each plaque sample. Student's paired t-test was applied for comparing saliva and plaque samples bacterial vitality at different time periods.

Results: The mean bacterial vitality in saliva and plaque under basal conditions was 92% and 80% respectively (p= 0.006). At 30 seconds, 1 and 3 hours after CHX mouthrinsing the levels of viable bacteria detected in saliva and plaque were similar (saliva: 5%, 19% and 43% respectively; plaque: 4%, 16% and 35% respectively). The percentage of live bacteria detected in saliva was significantly higher than that observed in plaque at 5 hours (58% versus 23%, p= 0.002) and at 7 hours after CHX mouthrinsing (70% versus 30%) (p< 0.001).

Conclusion: The 0.2% CHX solution showed lower sustained antibacterial activity on salivary flora than on de novo plaque at 5 and 7 hours after mouthrinsing. This could express the possible reservoir function associated to the biofilm.

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