 One hour prior the sampling, the participants were asked to abstain from smoking and consuming any food and drinks. After rinsing of the oral cavity for three times with tepid water in order to remove exfoliated cells, a swab was taken by gently brushing the buccal mucosa bilaterally with a cytobrush Cytobrush Plus, GmbH, Dietramszell-Linden, Germany and then the samples were applied to coded laboratory glass slides pre-warmed at 37 C. 