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8/7/2019 Dental Plaque Final
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Introduction
Several hundred different bacteria, fungiand protozoa live in oral cavity.
When these adhere to some surface they
form an organized structure called dentalplaque.
Dental Plaque can be defined as soft
deposit that forms biofilm adhering to thetooth surface or other hard surface in oral
cavity including removable and fixed
restoration (Bowen 1973)
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Ecology is the study of interrelationship of
organisms and their environment where as
Niche is defined as specific combination of
physical, chemical and biological
parameters that are necessary for survivalof particular organism.
Organisms that occupy niches that are
compatible with conditions available in
newly changed environment, the pioneer
species are first to recolonize.
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Pioneer species by changing environment
can enable new organisms to exists inenvironment.
The process by which organisms
sequentially inhabit altered environment is
known as ecological succession.
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The Oral Ecosystem
Number of factors determine which
organisms are able to survive in the
mouth and which of oralmicroenvironment they inhabit.
The factor are divided into three
categories
a) Physicochemical factors:
1 Temperature.
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2 Oxygen tension
3 Hydrogen ion concentration
4 Availability of nutrients.
b Host factors:
1 Saliva
1a Antibodies
1b Glycoprotiens
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1c Nonspecific enzymes like lysozymes,
lactoferrin and lactoperoxidase.
2 GCF
3 Complement
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c Bacterial determinant:
1 adherence
2 interaction with other microbes
Factors under hosts control:
1 Oral hygiene
2 Dietary habits
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Dental pellicle formation
Dental plaque may be considered as
dense, noncalcified bacterial mass so
firmly adherent to tooth surface that they
resists wash off by salivary flow.
The pellicle is an amorphous,membranous layer which covers the
enamel surface and is often 0.1 to several
micron thick.
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The acquired pellicle forms immediately after
eruption or cleaning (Al Hashmi and Levine1989) and directly influence pattern of
colonization.
Salivary pellicle usually consists of albumin,
lysozome, amylase, cystine, containing
phosphoprotiens like immunoglobulin A,
lactoferrin and proline rich proteins like
statherin and mucins.
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Proline rich proteins enhance attachment
of A. viscosus.
Other proteins bind specifically y to plaque
organisms and therefore presumably could
also function as receptors for attachment.
Other salivary glycoproteins have been
found to agglutinate specific plaque
bacteria.
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In some cases removal of these salivary
protein results in reduction of adhesion
activity of saliva, that is the relationship of
these salivary agglutinins to salivary
adhesion receptor.
Mandel and Ellision have hypothesized
salivary agglutinins function as sort of ready
to wear molecules that clump bacteria and
result in enhanced clearance from oral
cavity.
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The interaction involves a number of low
affinity binding reaction the sum of whichprovides the necessary stability for adhesion
to occur.
The adsorption of salivary constituents
occurs within minutes after pellicle is
removed from teeth by vigorous pumicing
and adsorbed material eventually become
transformed in to highly insoluble protein.
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The importance of salivary pellicle in
attachment is illustrated by experiments by
Slots.
Two enamel slabs of uniform size are
obtained and polished one of the slabs is
dipped into saliva diluted with buffer, the
other slab is dipped into buffer alone.
Both slabs are allowed to air dry, after
which they are placed in culture of S.
sanguis containing approximately 108cells
per ml.
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The slabs are removed and washed with
moderate water spray. They found more
bacteria binds to slab coated with saliva,
than to naked slab. They also found inspite of rather large number of bacteria
available, relatively few bind to pellicle.
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In past formation of cuticle or pellicle was
considered to constitute initial phase and
was believed that additional mucinous
material precipitated on this layer.
Bacteria were thought to adhere to, to
passively invade, or to become entrapped in
mucinous layer. These hypothesis were
supported by Mc Dougall who described a
thick bacteria free layer termed immature
plaque.
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However studies have failed to confirm
existence of immature plaque layer.
Mucin precipitation was hypothesized to be
due to
1 Local production of acids by bacterial
deposits on teeth or by acidification of saliva.
2Action of calcium ions
3 Alteration of salivary mucin by bacterial
enzymes.
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Dawes showed that precipitation could not
be detected during careful acidification of
saliva.
Leach et al suggested that neuraminidase an
enzyme which cleaves the terminal sialicacid residues from salivary mucin could
cause mucin precipitation.
It was found that plaque contains little or nosialic acid and that many oral bacteria
produced neuraminidase
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But recent studies have shown that
supragingival plaque has openarchitecture with open channels traversing
from outside of biofilm to enamel surface.
(Wood et al 2000, Auschill et al 2001,
Zaura Arite et al 2001)
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Early colonizers
Organisms that occupy niches that are
compatible with conditions available in newly
changed environment, the pioneer species are
first to colonize. The plaque formation involves specificity at
several levels.
1 initial bacterial colonizers.2 salivary receptors.
3 bacterial surface molecules ( adhesins)
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4 functional domains of both adhesins andreceptor that interact.
If brushing is suspended small isolatedplaque colonies form in 1 to 4 days.
In 2 to 5days the colonies fuse to form acontinuous deposit.
The initial colonizers are usually grampositive cocci cells.
These usually include member of yellow orpurple complex.
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The initial bacteria colonizing pellicle coated
tooth surface are gram positive facultativeorganism such as A. viscosus and S. sanguis
and S. gordinii.
Two types of adhesive interactions are
required for a plaque to form (Gibbons and
Gibbons 1971)
First bacteria must adhere to pellicle surface
in order to initiate plaque.
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Secondly an adhesive interaction must
occur between bacterial cells mediated bycomponents, comprising matrix of plaque
to permit organism to accumulate and to
impart cohesive properties of plaque.
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Bacterial cohesive interactions mediated by
extra cellular polymers:
The best example of interbacterial
adhesion mediated by synthesis of
bacterial polymers concerns S. mutans. Gibbons was first to point that S. mutans
produced an insoluble polymer.
It produced extra cellular polysaccharide
consisting of glucans and fructans from
sucrose
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Organisms that produce larger quantities of
Alpha 1-6 linkage polysaccharides stick
better to tooth surface.
In fact the initial attachment of S. sanguis to
pellicle is 10 fold greater than S. mutans.
Lipoteichoic acids are amphipathic linear
molecules in which end usually has lipid
moieties and is hydrophobic. The other end
is composed of repeating unit of glycerol
phosphate and is negatively charged.
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One hypothesis is that charged phosphate
forms calcium bridge with sulfated
glycoprotein in salivary pellicle.
But adhesion to teichoic acid do not
prevent adherence, whereas antibodies to
Streptococcal surface protein antigen are
effective inhibitors of in vitro plaque which
is converse to above theory.
The most effective adhesins activity is by
surface proteins
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Many strains of S. sanguis and S. mitis are
unable to form cohesive, plaque like
deposits. But these organisms are presentin plaque in significant proportions.
Data available indicate that plaque bacteria
can interact with salivary constituents.
Separate mucinous polymers are involved
in aggregation of S. sanguis and S. mitis
(Kashket1962)
and calcium ions are required in both
cases. (Gibbons and Kashket 1972)
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The salivary agglutinating system for S.
mitis has a number of characteristic which
suggests its importance in plaque
formation.
Besides adsorbing to surface of
Streptococcal cells there by causing
aggregation, the salivary components can
interact intermolecularly thereby forming
insoluble complexes. (Hay and Gibbons
1971)
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Bacterial tendency to become insoluble and
their relative biologic stability suggests theycould exists as plaque matrix components
for significant period of time.
Salivary constituents involved in
aggregation of S. mitis have also been
found to adsorb selectively tohydroxyapatite and therefore are likely to
constitute part of enamel pellicle.
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The ability of saliva aggregating material
to react intermolecularly, its adsorption tobacterial surface, its apparent presence in
plaque matrix as well as its adsorption to
hydroxyapatite, all suggests its
involvement in initial attachment of
bacteria to enamel. Calcium ions play an important role in
plaque formation.
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Jenkins (1968) has considered the
possibility that calcium ions could inducematrix formation by enhancing mucin
precipitation.
Silverman and Kleinberg (1967) have
shown pooled plaque can be partially de-
aggregated by NaOH and resultingsuspension will re aggregate when pH is
lowered and calcium ions are added
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The requirement of calcium ions for specific
salivary components which adsorb to
bacterial surfaces and cause their
aggregation may explain why calcium
appears to be involved in matrix formationand imparts cohesive properties to plaque.
In addition to salivary glycoproteins with
bacterial aggregating activities plaque has
also been found to contain Ig A
(Taubman1972
) and serum albumin.
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Both Ig A and albumin are well known to
bind to bacteria and consequently their
presence in plaque is also likely due to
their affinity for bacteria.
Salivary components could become
incorporated into plaque by binding to
bacteria prior to attachment to teeth.
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Plaque cohesion could be accomplished by
either single salivary polymer binding twobacterial cells together or by salivary
coating of one cell interlacing salivary
coating of another.
Salivary polymers are not found
subgingivally (Baumhammers and Stallard1966) hence components of GCF may play
role analogous to saliva.
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Plaque initiation and interaction of
bacteria:
Initial phase consists of adhesive
interaction between surface component of
bacteria and substance present on enamel.
The enamel pellicle is formed by selective
adsorption of salivary components to teeth.
A similar selectivity is involved in
adsorption of bacteria to pellicle surface
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Once bacteria are attracted to a surface,
firm attachment requires several hours
during which extra cellular polymeric
materials are synthesized. (Marshall et al
1971)
Thus initial phase of bacterial adsorption
can be considered reversible and it may or
may not become irreversible over a time
(Marshall et al)
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The adsorption of some bacterial species
is either enhanced while that of others is
either unaffected or reduced.
This adsorbed salivary layer has been
found to increase adsorption of strains of
S. sanguis and S. mitis. In general,
organism which are aggregated by salivarymacro molecules display an enhanced
adsorption.
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It is suggested that bacterium which
normally possess a negative charge may
through kinetic energy approach a natural
surface which also possess a negative
charge.
As the cell approaches, Van der Waals
forces begin to exert an attractive force, butnet negative charges on both cells and
surface increasingly repel each other
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Hence organisms will stay in a state of
equilibrium, where a balance exists between
repulsive effect of negative charge and
attractive influence of Van der Waals forces
on the other hand.
At this point adsorption is reversible and cell
is situated at a distance from surface.
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If macro molecules are introduced which
can bridge the space between cells and
surface and effectively link both together
hydrogen, electrostatic- hydrophobic or
other bond, adsorption will become
irreversible.
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But studies have suggested the following
concepts of plaque formation: (P.D. Marsh
2004) They have channels and voids.
Production of extra cellular polymers to
form functional matrix. Production of cell- cell signalling
molecules ( CSP; autoinducer2).
pH and O2 gradients, co-adhesion. Obligate anaerobes in an overtly aerobic
environment.