Dental plaque
Lectuer (4)
Dr. Baha , Hamdi .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 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
Pellical:it is a layer of material on tooth surface 
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 favors 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. 

StagE1-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
Plaque Development: 
Gradually the micro colonies producing 
complex three dimensional arrangement
The resultant biofilme is called dental

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 . 
The
End
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