O formation in the human mouth is dependent on salivary NO
- concentrations and the presence of dental plaque. (a) Correlation of oral N2O production and salivary NO2-/NO3- concentration in 15 volunteers with unbrushed teeth. Each data point represents the rate of oral N2O accumulation of one individual on a certain day (black circles). Some volunteers were sampled on more than 1 day resulting in 19 data points in total. Four volunteers were additionally sampled before and after drinking NO3--rich beetroot juice to increase salivary NO2-/NO3- concentration and oral N2O accumulation (white circles connected by dotted line). (b) Effect of oral hygiene on N2O accumulation rate in the mouth. Oral N2O accumulation rate of individuals before tooth brushing plotted against the N2O accumulation rate after tooth brushing (closed circles). In six individuals an antiseptic mouth rinse that affects bacteria in the entire oral cavity was applied after tooth brushing (open circles, each of the six individuals is represented by a unique colour). For example, an individual (dark green) with an oral N2O accumulation rate of 500 nmol/h reduced the rate to 290 nmol/h by tooth brushing. Subsequent application of a mouth rinse resulted in a rate of 110 nmol/h. The dashed line corresponds to the absence of an effect of oral hygiene on the oral N2O accumulation. The error bars indicate the standard error of five replicate measurements of the oral N2O accumulation rate.