【正文】 gnized system “adhesions” →”receptors” Simplified explanation of the principle of selective adherence of bacteria to enamel. Successful attachment is achieved when the surface characteristics of a bacterium fit with a ponent in the pellicle (P) Tworeaction process for initial weak attachment occurs between bacterial cell proteins and salivary glycoproteins of the acquired pellicle and is followed by cellular accumulation mediated by sucrosedependent glucans and cell surface receptor ligands. The adherence of selected oral bacteria initially involves non specific, lowaffinity, very rapid binding reactions followed by specific, highaffinity, slower, but stronger attachment to the acquired pellicle Microbial succession Receptors (oligossacharides) has a glactosehinding adhesin Actiuomyces viscosus → proline rich protein Statherin → sialic acid Pioneer bacteria create an environment which is either more attractive for secondary invaders or increase unfavorable condition to themselves. In this way the resident microbial munity is gradually replaced by other species In mature dental plaque there may be a subtle balance(homeostasis) that tends to eject invading species not previously present. Structural features of microbial colonization Initial microbial deposition after a cleaned tooth surface has been exposed for 4h to the oral environment, surprisingly few bacteria are found (one of reports) After 4 hours exposure the enamel is covered by pellicle which is a granular deposit, primarily located in Tomes processes pits (TP) and in perikymatal grooves (P) The first bacteria to colonize the tooth surface are of the coccobacillary type (B ).note that the granular deposit does not cover the tooth surface in a uniform layer (PE) At this early stage bacteria are of the coccid or coccobacillary type and always reside in shallow depressions on the surface After 8h only a few smaller groups of microanisms have settled on the surface sheltered by the perikymata Numerous bacteria spread across the surface as a monolayer In 12hold bacterial deposits the microanisms spread in monolayer along the perikymata (P ) In same areas multiplying microanisms form multiplayer, individual anisms are embedded in an intermicrobial matrix. The monolayer of bacteria (upper part) is gradually replaced by a multiplayer (lower part )which is embedded in an intermicrobial matrix (X) ? Within 1 day the tooth surface is almost pletely covered by blanket of microanisms ? monolayer are intermitted with multilayers. After 1 day the surface of the microbiota is mainly made up of coccoid bacteria, with a few filaments During the course of the 2nd day the bacterial deposits are colonized by multiple filamentous anisms with a perpendicular orientation to the surface Distinct morphological changes may be recorded on the surface of the microbiota when paring the bacterial deposits after 24 (Fig. 512) and 48 h(). Whereas the 24hold bacterial deposit prises a mass of coccoid bacteria from which a few filaments extend, the 48hold microbiota is almost entirely dominated by filamentous anisms28 Initial colonization of root cementum occurs in principle as outline for enamel surface, but process more rapidly Because of the irregular surface to topography of root surfaces, colonization does not take place according to a particular pattern 48hold bacterial deposits on root cementum and enamel surfaces from the same individual. Note that the microbial deposits are thicker and more densely packed on root cementum mature dental plaque During the early days, plaque growth occurs mainly as a result of cell division, but continuous adsorption of single microanisms from saliva also contributes to the expansion of the bacterial deposit The corn cob are posed of a central filament coated with spherical anisms, and appear to have a direct interspecies relationship machinated by surface fibrils As the microbiota grows older, characteristic structural changes are noted deep to the surface. The most striking change is the formation of an inner layer of densely packed grampositive pleomorphic bacteria next to the tooth surface Ultrastructure of 2 weekold dental plaque from 3 individuals with different colonization patterns. Note that , in addition to differences in thickness, the outer parts of the deposits vary in position and structure. Relative proportions of selected anisms in developing supragingival plaque on the labial surface of incisors. Plaque samples were obtained 1,3,5,7, and 9 days after thorough prophylaxis. Chemical position of plaque plaque contain about 80% water 20% solids protein 40% to 50% carbohydrates account for 13% to 18% lipids account for 10% to 14% other Direct smears Count of 2 1011 microanisms/g In centrifuge 3 1011 anisms/g 2/3 of plaque must consist of bacteria that means 70% the area is posed of microanisms and 30% of intercellular material (matrix) Carbohydrates of plaque ? Glucose is the main carbohydrate found in hydrolyzed extracts of plaque ? arabinose ? ribose ? galactose ? fucose Much of the carbohydrate exists in the form of extracellular polymers ? glucans (homopolymers of glucose) ? fructans (homopolymers of fructose ) ? Heteropolysaccharides Plaque microanisms forming extracellular polysaccharides Glucans Fructans Heteropolysaccharides Streptococcus sanguis Actinomyces viscosus Actinomyces viscosus Streptococcus mutans Streptococcus mutan