Dental plaque Dr.Baha.Hamdi AI-Amiedie

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 secounds on cleaned enamal and reaches a maxmum 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

Stagr1-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)

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 2-Initial adhesion

Stage 3-Attachment: More permanent attachment can occuer

by covalent, ionic or electrostatic bonding these bonds form between specific receptors on host surface termed ligands, and component situated on bacterial appendeges 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

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)