In my study I have tried to show recent discoveries concerning the composition of plaque, its microscopic structure and the role it plays in etiopathogenesis of periodontitis. Dentobacterial plaque is bacterial film which adheres to the surface and presents the main cause of periodontal diseases. There are two kinds of plaque: subgingival and supragingival. It develops in three stages. The first stage is the formation of pelicula, followed by population of microorganisms which proliferate and create colonies. The products of plaque reach subepitel fibres, causing infections such as increase of blood flow and diapedesis of leucocites. Both supragingival and subgingival plaque form hard, mineralised calculus masses. Bacteria adhere to the surface of the calculus, increasing infection which results in final destruction of periodont. I have also listed the newest world researches dealing with the composition of plaque and its role in developing aggressive and chronic periodontitis. Recent stomatological studies show the importance of profilacsa; since removing the plaque also results with removing large parts of microflora on dental surface and marginal parodont. Nowadays we try to reduce significantly marginal parodontal infections promoting regular oral hygiene, the usage of oral antiseptics, reduction of refined carbohydrates in nutrition, resulting in minimisation of plaque voluminosity. An effective oral antiseptic must have an impact on gram-positive and gram-negative bacteria, including streptococs and fusobacteria. Bacteria layers must be removed in order to achieve better penetration of such agent. It is important to discover the presence of periodontal pathogens as early as possible in order to prevent diseases. There are different methods of detection, but the most frequently used technique is the polimerase chain reaction (PCR). With this technique it is possible to detect even the smallest number of microorganisms or their DNAs.