Bacteria and saliva play a very important role in the arising of the oral diseases. It must be considered that the saliva gives the nutriments for the bacteria, and it is able to influence the adhesive mechanisms, and to escape these bacteria. The interaction between the saliva and the host is unknown, but it is well-known in vitro, through the oral ecological systems principles. The authors reviewed several works about the salivary components and their role so in vivo, either in vitro. In this work, first the authors looked for these salivary components, and then, examined the interactions between the saliva, the plaque and the bacteria. So the saliva is a fundamental component in the ecologic succession, and it is nearly related to the etiopathogenesis of periodontitis. Finally a best knowledge of the saliva role and its components in the periodontitis is very interesting, because some salivary components allow the root surfaces colonization, exposed to the oral fluid and they give the possibility to use salivary components as markers of any disease.