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 supragingival 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
formation: There are four stages in plaque
1-transport.
2-initial adhesion.
3-irreversible attachment.
4-colonization.
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)
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 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
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 .