It has been shown that several oral diseases were associated with changes in nitric oxide concentration. Smoking may be involved in the pathogenesis of the diseases by affecting on salivary nitric oxide levels. The aim of this study was to compare the salivary nitric oxide levels between smokers and nonsmokers. In this case-control study, smokers as cases and age/gender-matched nonsmokers as controls were selected. Participants were asked to avoid eating, drinking, dental brushing or flossing for two hours before taking saliva specimens. Samples of unstimulated saliva were collected. Nitric oxide levels were measured by Griess reaction method. Data were analyzed by SPSS using Kolmogorov-Smirnov and Mann-Whitney tests, and multiple linear regression and Spearman correlation coefficient (P<0.05). Forty-four smokers, as cases, including 19 males (43.2%) and 25 females (56.8%) aged 19-25 years and 38 nonsmokers, as controls, including 21 males (55.3%) and 17 females (44.7%) aged 20-25 years were studied. There was no significant difference in salivary nitric oxide levels between smokers (range: 2-552; median: 66.8 microM) and nonsmokers (range: 0.1-857; median: 71 microM) (P=0.996). Multiple linear regression analysis showed that gender and age variables had no significant effect on salivary nitric oxide levels (P<0.05). In smokers, the salivary nitric oxide level presented an indirect significant correlation to smoking rate in term of pack-year (P<0.001; r= - 0.525). These findings suggest that salivary nitric oxide levels were reduced by an increase in rate of smoking.
