Dental plaque Lectuer (4) Dr. Baha, H.AL-Amiedi Ph.D.Microbiology
it is now well established that caries & periodontal disease are infectious disease associated with resident microorganisms of dental plaque there are two hypothesis explain that: The specific plaque hypothesis: proposes that only a few microorganisms are involved in the oral disease process Non specific plaque hypothesis: considers that disease result from the interaction of the whole plaque with the host.
there are serveral organic deposits on the surface of the teeth these deposits include dental plaque, material alba, pellicle, calculus deposits, materia alba: so it is the outer portion of dental plaque is composed of an unorganized structure of microbial growth and desquamated epithelial &white &red blood cells loosely to organized structural portion of plaque and is easily removed by mechanical action of water spray. but if it with stand the water spray it is called dental plaque
Dental plaque: It is a general terms for the complex microbial community found on the tooth surface, embedded in a matrix of polymers derived from bacteria & saliva. For successful colonization microorganism must first adhere to a surface this involve interaction between a dhesins on the microbial surface and ligand s on the host surface
Dental plaque formation: adherence to a surface in the mouth is essential for survival of oral bacteria.in the cause of supra gingival plaque formation, Microorganism interact with a layer of material on tooth surface called pellicle comprises mucins, salivary glycoproteins, Minerals &immunoglobulin, the pellical formation occurs in seconds on cleaned enamel and reaches a maximum thickness in 90-120 minutes
Ecology plaque hypothesis: This hypothesis concerning to the main factors involve in dental caries(saliva, diet, tooth surface& plaque ecology) that when salivary composition & fermentable sugar intake are within normal limits, plaque ecology favours bacterial species that associated with a PH of 6-7 (streptococcus oralis& streptococcus sanguis) and intact enamel& dentine surface. However if the amount &frequency of intake fermentable
Sugar increases markedly, with or without changes in salivary composition&function plaque ecology favours acid-tolerating bacteria( strep mutans &lactobacilli spp) that are associated with low-ph less than5 and demineralized tooth surfaces.that show only two extreme situations(health& Disease)but in reality very wide range of possible interaction can occur involving the main a etiological factors some which tend towards demineralization &disease& others towards reminaralizaton&health
There are four stages in plaque formation: 1-transport. 2-initial adhesion. 3-irreversible attachment. 4-colonization.
Stage-1-Transport Bacteria must first approach the surface to which they will later bind by several way 1-liquied flow. 2-Diffusion through brown motion. 3-bacterial movement (chemotactic activity)
stage -2-Initial adhesion Two types of force are involved at this stage at distances of 10-100 nm : a-van der Waales b-electrostactic forces As bacterium approaches closer(2nm) Strong forces, such as hydrogen bonding between hydroxyl group in the pellicle &phosphate group in bacterial cell wall come into plaque.
Stage -3-Attachment: More permanent attachment can occur by covalent, ionic or electrostatic bonding these bonds form between specific receptors on host surface termed ligands, and component situated on bacterial appendages called adhesion such as fimbriae so oral bacterial attachment and therefore plaque formation is affected by factors of host and microbial &saliva.
Stage -4-colonization Once bond to surface, the bacterium can divide and remain attached extracellular products are formed and daughter cell repeat the process so that microcolonie develop,salivery glyco-proteins &dietery sugars such as glucose &sucrose can metabolized leading to the formation of bacterial cell wall, water-soluble&insoluble Polysaccharide are important in plaque formation
Plaque Development: Gradually the micro-colonies producing complex three dimensional arrangement The resultant biofilm is called dental plaque plaque maturation by increasing quantity &diversity of microorganisms on The tooth surface.after 7 days still streptococci the main organism present,but after 14 days there is a shift to anaerobic rods &filments, with comprising Only 15 % of streptococci
Microbial plaque: study of the dental plaque showed the following group in these percentage: Facultative streptococci 27 % Facultative diphtheroids 23 % Anaerobic diphtheroids 18 % Peptostreptococci 13 % Veillonella 6 % Bacteroides 4 % Fustobacteria 4 % Neisseria 3 % Vibrio 2 %
Chemical composition of plaque: contains * water75-80%, * protein 40-50%. Of dry weight * carbohydrate 13-18% of dry weight *lipid 10-14%. Of dry weight. Inorganic compound: calicum,phosphate phosphate, fluried &small amount of( mg, k)
Calculas: when dental plaque calcified;saliva is super-saturated by calicum,phosphat Ion,which accumulate within the plaque matrix together with organic debris from dead microorganisms,that lead to formation of insoluble calicum phosphate crystals,which coalesce to form calculus 20% organic compound 80%mineralized material.