Dental Plaque Final

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.

Dental Plaque Final

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