dental plaque ecosystem

DENTAL PLAQUE:ECOSYSTEM

Dr Midhun Kishor S

First year MDS

Department of periodontics and implantology

Rajas dental college and hospital

Ecosystem – complex of organisms in a specified

environment and the non microbial surroundings with

which the organisms are associated.

• Habitat - it is the site at which a population or community grows,

reproduces or survives.

• Niche - functional role of an organism in a habitat.

Marsh,P.D and Moter ,A and Devine,DA-dental plaque biofilms community conflict and control periodontology 2000 55,February 2011 16-35

Mouth as a microbial habitat

6 Major ecosystems ( niches)

1.The intra oral,supragingival ,hardsurfaces(teeth,implants,prosthesis)

2.Subgingival regions adjacent to a hardsurfaces including periodontal or

periimplant pocket

3.The buccal,palatal epithelium,and the epithelium of the floor of the mouth

4.Dorsum of the tongue

5.The tonsils

6.The saliva

CARRANZAS clinical periodontology 11th edition

PLAQUE

Dental plaque is defined as adherent intercellular matrix consisting primarly of proliferating microrganisms,along with a scattering of epithelial cells,leukocytes and macrophages

“Bowen WH: Nature of plaque, Oral science review 1976”

Dental plaque can be defined as the soft deposits that form the biofilm adhering to the tooth surface or other hard surfaces in the oral cavity, including removable and fixed restorations.

Carranza 9th edition

Dental Plaque is a(host-associated biofilm).

Biofilm is defined as the relatively

undefinable microbial community

associated with a tooth surface or any other

hard, non-shedding material.

Biofilms are defined as “Matrix—enclosed

bacterial populations adherent to each

other and or/to surface or interfaces(by

Costerton).


BIOFILM-STRUCTURE

Microcolonies of

bacterial cells that are

randomly distributed in

shaped matrix or

glycocalyx

Exopolysaccharides

are the backbone

of biofilms

EPS is produced

by bacteria in the

biofilm and

makeup up to 50%

to 90% dry weight

Quorum sensing- ability

of bacteria and

microcolonies with in

the biofilm to

communicate with one

another

Quorum sensing

signalling

molecules are

produced by

putative

pathogens such as

P.gingivalis,prevote

lla intermedia and

F.nucleatum

Dental biofilms: difficult therapeutic targets.Socransky &Haffajee Periodontology 2000, Vol. 28, 2002

HOW BACTERIA COMMUNICATE TO EACH OTHER

Kolenbrander,PEAndersen RN,Blehert,communication among oral bacteria,microbiology and molecular biologyreviews 66,486-490

Key factors in quorum sensing

Quorum Sensing:Cell-to-Cell Communication in Bacteria :Christopher M.Waters and Bonnie L. Bassler,DepartmentMolecular Biology, Princeton University, Princeton, New Jersey

QUORUM SENSING SYSTEMS 1. QS used for intra species commuinication

-a. QS used by gm –ve bacteria

-b. QS used by gm +ve bacteria

2. QS used for inter species communication

LuxI/LuxR–type

in Gram-negative bacteria, which use AHL(aceyl homoserine lactone)

(2) Oligopeptide-two-component-type quorum sensing

in Gram-positive bacteria, which use small peptides

(3) luxS-encoded autoinducer 2 (AI-2) quorum sensing

in both Gram-negative and Gram-positive bacteria.

Quorum Sensing:Cell-to-Cell Communication in Bacteria :Christopher M.Waters and Bonnie L. Bassler,Department of Molecular Biology, Princeton University, Princeton, New Jersey

Significance of a biofilm and community life style for microorganisms

Biofilms are matrix embedded microbial

populations adherent to each other and or to

surfaces or interfaces

Ability to attach and to be retain at a surface is the fundamental

survival strategy for most of the prokaryotic organisms

Microbes found in multispecies biofilms are not randomly distributed but are spatially

and functionally organized

Bacterial gene expression can alter markedly when cells form a biofilm resulting in organisms having radically

different phenotype following attachement to a surface

Oral biofilms and Calculus – text book of Clinical periodontologyand Implant dentistry - Jan Lindhe, Lang and Karring – 5th Edition

Most natural biofilms contain multiple species that engage in a wide range of physical,metabolic and molecular interactions and are termed as microbial communities

An important clinical consequence of both the structural and functional organization of multispecies biofilm is their reduced succeptibility to antimicrobial agents

Minimum inhibitory concentration of an organism growing on a surface can be from 2-1000-fold greater than that of the same cells grown planktonically with older biofilms


Bacteria exists and

proliferate with in the

intercellular matrix through

which the channels run

The matrix conferes a

specialized

environment that

distinguishes the

bacteria that exists

with in the biofilm

from those that are

free

floating(planktonic

state) in solutions

The biofilm

functions as a

barrier

Substancs produced

with in the biofilm

are retained and

concentrated which

fosters metabolic

interactions among

different species


Types of dental plaque

Based on its relationship to the

gingival margin, plaque is

differentiated into two

categories :

supragingival plaque subgingival plaque

Periodontal microbial ecology. Socransky &Haffajee Periodontology 2000, Vol. 38, 2005

SUPRA GINGIVAL PLAQUE

It can be detected clinically only after it has reached a certain thickness.

Small amounts of plaque can be visualized by using disclosing agents.

The color varies from gray to yellowish-grey to yellow.

SUBGINGIVAL PLAQUE

It is usually thin, contained within the gingival sulci or periodontal pocket and thus CANNOT be detected by direct observation.

Its presence can be identified only by running the end of a probe around gingival margin

Tissue attached is usually demonstrated in ANUG and localized aggressive periodontitis patients.

Kuboniwa M and Lamont,Rj subgingival biofilm formation periodontology 2000 52ed

Composition of Dental

Bacteria + Intercellular matrix = Dental plaque

80% water20% solids, includes cells mainly bacteria making up 35% of the dry weight and extracellular components making 65% of the dry weight.Other than bacteria, non bacterial organisms include:

MycoplasmaYeastProtozoaViruses

Host cells in Dental plaque.Epithelial cellsMacrophagesLeukocytes


The ORGANIC matrix is composed of protein—

polysaccharide complex produced by microorganisms.

Carbohydrates in the form of levans (fructans)

provides mainly energy while glucans (dextran)

provide NOT only energy, but also act as the organic

skeleton of plaque.

Other carbohydrates are galactose and rhamnose.

Glycoproteins provide the protein component and

small amounts of lipids are also presentInorganic components include, primarily

calcium, phosphorus with small amounts of magnesium, potassium and sodium.

EXOPOLYSACCHARIDES

Exopolysaccharides (back bone)produced by the bacteria, are the major components, making up 50–95% of the dryweight .

EPS includes insoluble glucans, fructans and heteropolymers.

can produce several different polysaccharides depending on the physiological state and the presence of specific substrates.

Glucans are synthesized by glucosyltransferase (GTF). GTFs can be secreted or adsorbed onto other bacteria, acquired pellicle.

Fructans are produced by fructosyltransferases (FTF) which are short lived and act as nutrient storage compounds for use by other bacteria

Microbial Exopolysaccharides: Biosynthesis and Potential Applications-Oriental journal of chemistry

DEVELOPMENT OF DENTAL PLAQUE

CARRANZAS clinical periodontology second south asia edition

Formation of the pellicle

Vigorous tooth brushing – nanoseconds – acquired pellicle .

Acquired pellicle - a homogenous, membranous, acellular film that covers the tooth surface and frequently form the interface between the tooth ,the dental plaque and calculus. (Schluger)

`A fully established pellicle - 30 min, within 24 hr- 0.8 µm in diameter.

Derived from components of saliva and crevicular fluid as well as bacterial and host tissue cell products and food debris.

Transmission electron micrograph (TEM) of the acquired pellicle on an enamel surface

Salivary pellicle can be detected on

clean enamel surfaces within 1

minute.

By 2 hours, the pellicle is essentially in

equilibrium.

Thickness - 30 - 100 nm

2 hr pellicle: Granular structures which form

globules, that connect to the Hydroxyapatite

surface via stalk like structures.

24 hrs Later: Globular structures get covered up

by fibrillar particles : 500 - 900 nm thick

36 hrs Later: The pellicle becomes

smooth, globular

Mechanism involved are:Electrostatic forces

Van der waalsHydrophobic forces


Initial Adhesion and Attachment of

Bacteria

PHASE I. Transport to the surface

2.Bacterial Adherence

During initial adherence, interactions occur mainly between specific bacteria and the pellicle. They are:

1- Bacterial Attachment via Electrostatic Interactions

Oral bacteria bear an overall net negative charge, negatively charged components of the bacterial surface and negatively charged components of pellicle become linked by cations such as calcium


2- Bacterial Attachment via Hydrophobic Interactions

These interactions are based on the close structural fit between molecules on the pellicle and bacterial surfaces.

The nature of the hydrophobicity of the cell is not clearly known.

The contributing factor might be lipoteichoic acid (LTA), may provide a long hydrophobic area .

Lectins in the bacterial surfaces recognize specific carbohydrate structure in the pellicle and become linked.

Overview of microbial biofilms. Costerton. Journal of Industrial Microbiology (1995) 15, 137-140

Colonization and plaque maturation

Primary colonizers

They provide new

binding sites for

adhesion by other oral

bacteria.

The metabolic activity of

the primary colonizers

modifies the local micro

environment which

influences the ability of

other bacteria to survive

in the dental plaque

biofilm.

The early colonizers

(e.g., streptococci and

Actinomyces species)

use oxygen and lower

the reduction-oxidation

potential of the

environment, which then

favors the growth of

anaerobic species

Secondary colonizers

They do not initially colonize the clean tooth surface but adhere to bacteria already in the plaque mass.

Periodontal microbial Ecology – Socransky and HaffajeePeriodontology 2000 – Volume 38 – 2005

Primary colonization by predominantly Gram-positive facultative bacteria. Ss: Streptococcus sanguis is most dominant. Av: Actinomyces spp. are also found in 24 hr plaque

Gram-positive facultative cocci and rods co-aggregate and multiply.

Surface receptors on the Gram-positive facultative cocciand rods allow the subsequent adherence of Gram-negative organisms, which have a poor ability to directly adhere to the pellicle.Fn: Fusobacterium nucleatum.BI: Prevotella intermedia.


The heterogeneity increases as plaque ages and matures. As a result of ecologic changes, more Gram-negative strictly anaerobic bacteria colonize secondarily and contribute to an increased pathogenicity of the biofilm

.Oral biofilms and Calculus – text book of Clinical periodontologyand Implant dentistry - Jan Lindhe, Lang and Karring – 5th Edition

Co-aggregation is the interaction between planktonic micro-organisms of a different strain or species

Co-adhesion is the interaction between a sessile, already adhering organism and planktonic micro-oganisms of a different strain or species

Co-aggregation

It was described by Gibbsons & Nygaard

Cell to cell recognition of a genetically distinct partner cell type.

Occurs primarily through

Highly specific interaction of proteins and carbohydrate molecules located on the bacterial cell surfaces.

Less specific interaction resulting from hydrophobic electrostatic & van der waals forces.

.CARRANZAS clinical periodontology second south asia edition

Well characterized interaction include the coaggregation of:

Fusobacterium nucleatum S. sanguis,

Prevotella loescheii A. viscosus

Capnocytophagea ochraceus A. viscosus

Streptococci show intrageneric co-aggregation bind to the nascent monolayer of already bound streptococci.

Later stages – coaggregation between different Gram negative

species seen – F. nucleatum & P. gingivalis or T. denticola.

.Kolenbrander,PEAndersen RN,Blehert,communication among oral bacteria,microbiology and molecular biologyreviews 66,486-490

Co aggregated Bridges

Formed when the common partner bears two or more types of coaggregation mediators.

Mediators can be various types of receptor polysaccharides, or various types of adhesins (lectin), or a mixture of the two.

Bridging is usually considered to be a cooperative event that brings three or more cell types into close proximity and fosters symbiotic relationships.

Bridging can also be an antagonistic event which brings together organisms that compete with each other for nutrient or other needs.

F. nucleatum and Late colonizers

F. nucleatum categorized as bridging organism

1.more numerous in healthy sites and they are

found in increased number in diseased sites

2.coaggregates well with all early and late colonizers

3. provide ideal anaerobic condition for the growth of

P.gingivalis

.Kolenbrander,PEAndersen RN,Blehert,communication among oral bacteria,microbiology and molecular biologyreviews

66,486-490

COAGGREGATION COMPETITION

Competition occurs when multiple cell types recognize the same co aggregation mediator on the common coaggregation partner

Model depicting competition for binding sites on Streptococcus oralis

Corncob formation

Feature of plaque present on teeth associated with gingivitis .

Rod-shaped bacterial cells eg. Bacterionema matruchotii or Actinomycessp. that forms inner core of the structure and coccal cells eg. Streptococci or P. gingivalis that attach along the surface of the rod shaped cells.

Test tube brush

Composed of a central axis of a filamentous bacterium with perpendicularly associated short filaments embeded in amorphous

Commonly seen in the subgingival plaque of teeth associated with

periodontitis

Detected between filaments of bacteria to which gram –ve rods adhere.

Many large filaments with flagella and is rich in spirochetes

.CARRANZAS clinical periodontology 11th edition

Test-tube brush found in subgingival plaque

Tannerella sp. (yellow) in a test-tube brush

Test-tube brush with Lactobacillus sp. (red rods) as central structures. F. nucleatum (green) and Bacteroides cluster filaments radiating from the central structures.

Transversal view of Streptococcus sp. (green) aggregation around a central cell (not stained) in supragingival plaque

CO-ADHESION

• Some bacteria are unable to bind directly to the conditioningfilm, but are able to interact with molecules on bacteria thatare already attached (co-adhesion), also by adhesin-receptorinteractions

• One bacterium, Fusobacterium nucleatum, can co-adherewith almost all other bacteria found in dental plaque, and isconsidered to be a key bridging organism between early andlater colonisers.

.Subgingival biofilm formation. Kuboniwa & Lamont. Periodontology 2000, Vol. 52, 2010

Development of dental plaque on a clean enamel surface. Coccal bacteria attach to the enamel pellicle as

pioneer species (A) and multiply to form microcolonies (B), eventually resulting in confluent growth (biofilm

formation) embedded in a matrix of extracellular polymers of bacterial and salivary origin (C). With time,

the diversity of the microflora increases, and rod and filament-shaped bacteria colonize (D and E). In the

climax community, many unusual associations between different bacterial populations can be seen,

including ‘corn-cob’ formations (F). (Magnification approx. × 1150)

Microbial Specificity of Periodontal Diseases

Non specific plaque hypothesis

The nonspecific and

specific plaque

hypotheses were

delineated in 1976 by

Walter Loesche

The nonspecific

hypothesis maintains

that periodontal

disease results from

the "elaboration of

noxious products by

the entire plaque flora.

According to this

thinking, when only

small amounts of

plaque are present,

noxious products are

neutralized by the

host.

Similarly, large

amounts of plaque

would produce large

amounts of noxious

products, which would

essentially overwhelm

the host's defenses.


Nonspecific plaque hypothesis is the concept that control of periodontal disease depends on control

of the amount of plaque accumulation.

Treatment of periodontitis by debridement

(nonsurgical or surgical) and oral hygiene measures

focuses on the removal of plaque and its products

and is founded in the nonspecific plaque hypothesis

Specific Plaque Hypothesis

It states that, not all plaque is

pathogenic.

Its pathogenicity depends on the

presence of certain specific microbial

pathogens in plaque.

This is based on the fact that, the

specific microorganisms responsible

for periodontal diseases release

certain damaging factors that

mediates the destruction of the host

tissue.


This concept was accepted easily due to

the recognition of Actinobacillus

actinomycetemcomitansas a possible pathogen responsible for localized

juvenile periodontitis.

Ecological plaque Hypothesis

Given by Marsh and Co-workers in 1990

Total amount of dental plaque and the specific microbial composition of plaque contribute to transition from health to disease

Health associated dental plaque microflora is considered to be actively stable overtime and on state of dynamic equilibrium or microbial homeostasis


Environmental plaque hypothesis

Haffajee and co workers in 1991

Entire subgingival microflora plays a key role in disease development

To develop periodontitis ,not only a susceptible host is necessary but pathogenic organisms must survive and multiply in large numbers within the subgingival film.

This is considered the most appropriate for chronic periodontitis.


Socransky's criteria for periodontal pathogens

ASSOCIATION: A pathogen should be found more frequently and in higher

numbers in disease states than in healthy states

ELIMINATION: Elimination of the pathogen should be accompanied by

elimination or remission of the disease.

•HOST RESPONSE: There should be evidence of a host response to a specific pathogen which is causing tissue damage.

•VIRULENCE FACTORS: Properties of a putative pathogen that may function to damage the host tissues should be demonstrated.

•ANIMAL STUDIES: The ability of a putative pathogen to function in producing disease should be demonstrated in an animal model system.

.Periodontal microbial Ecology – Socransky and Haffajee Periodontology 2000 – Volume 38 2005

REFERENCES1.Oral biofilms and Calculus – text book of Clinical periodontology

and Implant dentistry - Jan Lindhe, Lang and Karring – 5th Edition

2.Dental biofilms: difficult therapeutic targets.

Socransky &Haffajee Periodontology 2000, Vol. 28, 2002

3.Periodontal microbial ecology. Socransky &Haffajee Periodontology 2000, Vol. 38, 2005

4.Subgingival biofilm formation. Kuboniwa & Lamont. Periodontology 2000, Vol. 52, 2010

5.Microbial ecology of dental plaque and its significance in health and disease. Marsh. Adv Dent Res 8(2):263-271, July, 1994

6.Overview of microbial biofilms. Costerton. Journal of Industrial Microbiology (1995) 15, 137-140

7.Kolenbrander,PEAndersen RN,Blehert,communication among oral bacteria,microbiology and molecular biologyreviews 66,486-490

8. Quorum Sensing:Cell-to-Cell

Communication in Bacteria :Christopher M.Waters and Bonnie L. Bassler,Department of Molecular Biology, Princeton University, Princeton, New Jersey

9. Marsh,P.D and Moter ,A and Devine,DA-dental plaque biofilms community conflict and control periodontology 2000 55,February 2011 16-35

dental plaque ecosystem

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