The effects of essential oil, povidone-iodine, and chlorhexidine mouthwash on salivary nitrate/nitrite and nitrate-reducing bacteria

Dietary nitrate is reduced to nitrite and nitric oxide by microbial flora, and this activity is beneficial to vascular health. It has been reported that this bacterial process is inhibited by chlorhexidine mouthwash, although the effects of other products are largely unknown. This study examined the effects of several treatments on salivary nitrate/nitrite and nitrate-reducing bacteria. Twelve university staff and students performed mouth-washing with water (control), essential oil, 0.35% povidone-iodine, or 0.0025% chlorhexidine and then ate 100 g lettuce (110 mg nitrate content), followed by collection of saliva and tongue bacteria at the baseline, and 1, 5, and 10 h thereafter. The individual treatments were separated by an interval of one week. Salivary nitrate/nitrite was measured by the calorimetric method, and a representative nitrate-reducing bacterial species, Veillonella dispar, was detected and semi-quantified using a polymerase chain reaction (PCR) assay. Significant increases in salivary nitrate/nitrite were observed for all treatments (all P < 0.05). The PCR assay showed that water, essential oil, and povidone-iodine mouthwash had little effect, whereas V. dispar DNA bands were markedly inhibited after washing with chlorhexidine. These results suggest that essential oil and povidone-iodine mouthwash have little effect on oral nitrate-reducing activity. Salivary nitrite production was not reduced by chlorhexidine, but the fainter band of V. dispar DNA suggests that longer daily use might blunt this nitrate-reducing activity.