Biofilm - Periodontics

1. BIOFILM AND PERIODONTAL
MICROBIOLOGY
Department of Periodontology

2. CONTENTS: (PART- 1)
• INTRODUCTION
• HISTORY
• DEFINITION
• NATURE OF BIOFILM
• STRUCTURE OF BIOFILM
• COMPOSITION OF DENTAL PLAQUE
• EXOPOLYSACCHARIDES: BACKBONE OF BIOFILMS
• FORMATION OF DENTAL PLAQUE
• PROPERTIES OF BIOFILM

3. INTRODUCTION:
• Dental caries and periodontal diseases are among the most prevalent diseases known to man. Both are
associated with the bacteria contained in dental biofilm which is a complex, well organized structure.
Up to 500 bacterial species have been identified in it.
• Studies have shown that plaque accumulates rapidly on clinically plaque free teeth. For oral and
systemic health, the development and maturation of dental biofilm should be impeded and the dental
biofilm needs to be regularly and meticulously removed which could be done mechanical or chemical
means.
• Regular and diligent removal of supragingival dental biofilm is essential to prevent a large microbial
load from developing and to prevent the development of subgingival plaque and periodontal pockets.

4. HISTORY:
Biofilms are nothing new.
• The first description dates back to the 17th century, when Anton Von Leeuwenhoek - the inventor of
the Microscope, saw microbial aggregates (now known to be Biofilms) on scrapings of plaque from
his teeth.
• J Leon Williams (1897) – described dental plaque
• GV Black (1899) – coined term “gelatinous dental plaque”
• Waerhaug (1950) described the importance of bacterial plaque in the etiology of periodontal disease.
• Loe et al (1965), landmark study on plaque, saying that plaque is main etiological agent in
periodontal diseases.

5. • Schei (1959), Russel (1967) Epidemiological study- positive correlation between the
amount of bacterial plaque and the severity of gingivitis
• The term ‘Biofilm’ was coined by Bill Costerton in 1978.
• In 2002, Donlan and Costerton offered the most salient description of a biofilm. They
stated that biofilm is “a microbially derived sessile community characterized by cells that
are irreversibly attached to a substratum or interface or to each other, embedded in a matrix
of extracellular polymeric substances that they have produced, and exhibit an altered
phenotype with respect to growth rate and gene transcription.

6. DEFINITION:
• Biofilms have been defined as matrix embedded microbial
populations, adherent to each other and/or to surfaces or interfaces.
(Costerton et al.1995)
• The term Biofilm describes the relatively indefinable microbial
community associated with a tooth surface or any other hard non-
shedding material, randomly distributed in a shaped matrix or
glycocalyx. (Wilderer and Charaklis 1989)

7. • Dental plaque can be defined as the diverse community of microorganisms found on the tooth surface
as a biofilm, embedded in an extracellular matrix of polymers of host and microbial origin.
(Marsh 2004)
• 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)

8. • Dental plaque is a specific but highly variable structural entity, resulting from sequential
colonization of microorganisms on tooth surfaces, restorations & other parts of oral
cavity, composed of salivary components like mucin, desquamated epithelial cells, debris
& microorganisms, all embedded in extracellular gelatinous matrix.”
(WHO-1961)
• Bacterial aggregations on the teeth or other solid oral structures.
(Lindhe, 2003)

9. NATURE OF BIOFILMS:
Biofilms are preferred method of growth for most species of bacteria. This method of growth
provides a number of advantages to colonizing species:
1) A major advantage is the protection that the biofilm provides to colonizing species from
competing microorganisms & host defense mechanisms and from potentially toxic
substances in the environment, such as lethal chemicals or antibiotics.
2) Biofilm can also facilitate processing and uptake of nutrients, cross feeding, removal of
potentially harmful metabolic products (often by utilization by other bacteria) as well as
development of an appropriate physiochemical environment (such as a properly reduced
oxidation reduction potential).

10. 3) Communication between bacterial cells within a biofilm is also necessary for optimum
community development and is performed by the production of signaling molecules
such as those found in quorum sensing or perhaps by exchange of genetic information.
4) Detachment of cells from biofilms and establishment in new sites is important for the
survival of the biofilm dwellers.

11. STRUCTURE:
• Biofilms in general, have an organized structure. They are composed of micro colonies of bacterial cells
(15 – 20% by volume) non randomly distributed in a shaped matrix or glycocalyx (75% - 80% by
volume).
• In the lower plaque layers, which are dense, microbes are bound together in a polysaccharide matrix
with other organic and inorganic materials. On top of the lower layer, a loose layer appears that is often
irregular in appearance, it can extend into the surrounding medium (for teeth it is saliva).
• The fluid layer bordering the biofilm has a rather stationary sublayer and a fluid layer in motion.
Nutrients penetrate this fluid medium by molecular diffusion. Steep diffusion gradients, especially for
oxygen, exist in the more compact lower regions of biofilm, which further explains changes in the
microbial composition.

12. • Nutrients make contact with the sessile (attached) microcolonies by diffusion from the water channels
to the microcolony, rather than from the matrix. The bacteria exist and proliferate within the
intercellular matrix throughout which the channels run. The matrix confers a specialized environment,
which distinguishes bacteria that can exist within the biofilm from those that are free floating, the so
called planktonic state in solutions such as saliva or crevicular fluid.
• The dental plaque biofilm has a similar structure. It
is heterogenous in structure, with clear evidence of
open fluid filled channels running through the
plaque mass. These water channels permit the
passage of nutrients and other agents throughout
the biofilm, acting as a primitive “circulatory
system”.

13. • The biofilm matrix functions as a barrier. Substances produced by bacteria within the
biofilm are retained essentially concentrated, which fosters metabolic interactions among
the different bacteria.
• Microcolonies occur in different shapes in biofilms which are governed by the shear
forces due to the passage of fluid over the biofilm. At low shear force, the colonies are
shaped like towers or mushrooms, while at high shear force, the colonies are elongated
and capable of rapid oscillation. Individual microcolonies can consist of a single species
but more frequently are composed of several different species.

15. COMPOSITION OF DENTAL PLAQUE:
• The intercellular matrix consists of organic and inorganic materials derived from saliva, gingival
crevicular fluid and bacterial products.

16. • Organic constituents of the matrix include polysaccharides, proteins, glycoproteins and
lipid material. Albumin, probably originating from the crevicular fluid, has been
identified as a component of the plaque matrix. The lipid material consists of debris from
the membranes of disrupted bacterial and host cells and possibly food debris.
• Glycoproteins from saliva are an important component of the pellicle, which initially
coats a clean tooth surface, but also gets incorporated in to the developing plaque biofilm.
• Polysaccharides produced by bacteria, of which dextran is the predominant form, also
contributes to the organic portion of the matrix. They play a major role in maintaining the
integrity of the biofilm.

17. • The inorganic components of plaque are predominantly calcium
and phosphorous, with trace amounts of other minerals, including
sodium, potassium and fluoride.
• The source of inorganic constituents of supragingival plaque is
primarily saliva. As the mineral content increases, the plaque mass
becomes calcified to form calculus.
• The inorganic components of subgingival plaque are derived from
the crevicular fluid. The fluoride content of the plaque is derived
from the external sources such as fluoridated tooth pastes, rinses
and fluoridated drinking water.

18. EXOPOLYSACCHARIDES :
THE BACKBONE OF THE BIOFILM
• As mentioned above, the bulk of the biofilm consists of the matrix. It is composed
predominantly of water and aqueous solutes. The “dry” material is a mixture of
exopolysaccharides, proteins, salts and cell material.
• Exopolysaccharides which are produced by the bacteria in the biofilm, are the major
components of the biofilm, making up 50%-95% of the dry weight. The
exopolysaccharides can be degraded and utilized by bacteria within the biofilm. One
distinguishing feature of oral biofilms is that many of the microorganisms can both
synthesize and degrade the exopolysaccharides.

19. • Some exopolysaccharides are neutral, such as the mutan from the S. mutans whereas others are
highly charged polyanionic macromolecules. Different ionic charge and concentrations of
exopolysaccharides will alter the confirmation and cause rapid changes in the three dimensional gel
network of polysaccharides.
• Biofilm matrices are complex structures that contain masses of fibers of varying size, structure,
composition and rigidity that interact with each other with cells and with surface matrices. The
chemical composition and tertiary structure of the exopolysaccharides will determine whether it
forms an effective adhesive. It will also affect the hydrophilic or hydrophobic nature of the surface.

22. FORMATION OF THE PELLICLE:
• All surfaces of the oral cavity are coated with a thin saliva derived layer called the acquired pellicle.
• Acquired pellicle may be defined as a homogenous, membranous, acellular film that covers the tooth surface
and frequently form the interface between the tooth ,the dental plaque and calculus. (Schluger)
• This pellicle consists of numerous components, including glycoproteins (mucins), proline rich proteins,
phosphoproteins (eg: statherin), histidine rich proteins, enzymes (eg: α-amylase) and other molecules that
can function as adhesion sites for other bacteria receptors.

23. • Studies reveal that (2 hrs) enamel pellicle amino acid composition differs from that of saliva,
indicating that the pellicle forms by selective adsorption of the environmental macromolecules.
(Scannapieo FA et al , “ saliva and dental pellicles’” contemporary periodontics, 1990)
• The mechanisms involved in enamel pellicle include electrostatic, van der waals, hydrophobic
forces. The specific component of the pellicle depends upon the underlying surface.
• The physical and chemical nature of the solid substratum significantly affects several
physiochemical surface properties of the pellicle, including its composition, packing, density and
its configuration.

24. INITIALADHESION &
ATTACHMENT OF BACTERIA:
• Although, according to the present state of the art, no completely satisfactory picture of the bacterial
adhesion to hard surface exists, the following concept helps to understand most aspects of the adhesion
process.
• We cannot conclude a single mechanism that dictates the adhesiveness of micro-organisms.
(Scheie,1994)
• This concept approaches to the microbial adhesion to the surfaces in an aquatic environment as
following stage sequence:

26. Phase 1: Transport to the surface:
• The first stage involves the initial transport of the bacterium to the tooth surface. Random contacts
may occur, for example, through Brownian motion (average displacement of 40µm/hour), through
sedimentation of microorganisms, through liquid flow (several orders of magnitude faster than
diffusion) or through active bacterial movements (chemotactic activity).
• The first cells to adhere to pellicle on tooth surfaces or other solid surfaces are coccoid bacteria,
epithelial cells and polymorphonuclear leukocytes, the bacteria occur singly or as aggregates either on
or within the pellicle. During the first few hours, bacteria that resist detachment from the pellicle may
start to proliferate, forming small colonies of morphologically similar organisms.
• Plaque growth also may be initiated by microorganisms harbored in minute irregularities, such as
grooves in tooth surfaces, the margins of restorations, the cementoenamel junction and the gingival
sulcus, where they are protected from the natural cleaning of the tooth surface.

27. • The initial bacteria are called pioneer colonizers because they successfully compete with the other
members of the oral flora for a place on the tooth surface. After deposition, clones of pioneer colonizing
bacteria, S. sanguis, begin to expand away from the tooth surface to form columns that move outward in
long chains of palisading bacteria. These parallel columns are separated by uniformly narrow spaces.
Plaque growth proceeds by deposition of new species into these open spaces.
(Lisargten et al. 1975)
• The new deposited species attach to pioneer species in a specific molecular lock and key manner.
Expansion of existing species in a lateral direction causes the interbacterial spaces to merge. It is
hypothesized that, once the spaces are close enough, a starter substance is secreted by bacteria within the
plaque matrix stimulating a growth spurt in the surrounding bacteria.

28. • New bacteria, derived from saliva or surrounding mucous membranes now sense the bacteria laden
landscape of the tooth surface and attach by a bonding interaction to bacteria already attached to
the plaque. These associations called intergeneric coaggregations are mediated by specific
attachment proteins that occur between two partner cells. All this activity occurs within first 2 days
of plaque development.
• In addition to Fusobacteria acting as the principal co-aggregation bridge between early and late
colonizers, bridging among early colonizers is also possible. For example, co-aggregation between
P. loeschei and S. oralis is lactose inhibitable, and co-aggregation between P. loeschei and
Actinomyces israelii is lactose non inhibitable. S. oralis is not able to co-aggregate with A. israelii,
therefore, P. loeschei acts as a bridge of co-aggregation. Both A. israelii and P. loeschei co
aggregate with F. nucleatum, which co-aggregates with all the late colonizers.

29. Phase 2: Initial adhesion:
• The second stage results in a reversible adhesion of the bacterium, initiated by the interaction between
the bacterium and the surface, through long range and short range forces, including van der waals
attractive forces and electrostatic repulsive forces.
• Derjaguin, Landau, Verwey, and Overbeek (DLVO) have postulated that above a separation distance
of 1nm, the summation of the previous two forces describes the total long range interaction.
• The total interaction energy is also called the Total Gibbs energy (GTOT). The result of this summation
(GTOT = GA + GE), is a function of the separation distance between a negatively charged surface in a
medium ionic strength suspension medium (eg: saliva).

30. • GTOT for most bacteria consists of secondary minimum (reversible binding takes place: 5-20 nm
from the surface), a positive maximum (located at <2nm away from surface), where irreversible
adhesion is established.
• If a particle reaches primary minimum a group of short range forces dominates adhesive interaction
& determines strength of adhesion.
• Continuous plaque accumulation has formed along the gingival margin after 24 to 48 hours. The
plaque is dominated by Streptococci and a few rods. During the first 2 days, the plaque is
dominated by the relatively harmless normal microflora of the tooth surface, consisting of
facultative anaerobic gram positive Streptococci (S. sanguis and S. mitis) and a minority of gram
positive rods (Actinomyces species), which may impede infiltration of more pathogenic
microorganisms.

31. Phase 3: Attachment:
• After initial adhesion, a firm anchorage between bacterium and surface will be established by
specific interactions (covalent, ionic or hydrogen bonding). This follows direct contact or bridging
true extracellular filamentous appendages (with length up to 10 nm).
• On a rough surface, bacteria are better protected against shear forces so that a change from
reversible to irreversible bonding occurs more easily and more frequently. The bonding between
bacteria and pellicle is mediated by extracellular proteinaceous components (adhesions) of the
organism and complementary receptors (i.e. Proteins, glycoproteins or polysaccharides on the
surface (eg. pellicle) and is species specific.

32. • Each Streptococcus and Actinomyces strain binds with specific salivary molecules.
Streptococci (S. sanguis), the principal early colonizers, bind to acidic proline rich proteins and
other receptors in the pellicle such as α-amylase and sialic acid.
• Actinomyces species also function as primary colonizers; for example, A. viscosus posses fimbriae
that contain adhesins that specifically bind to proline rich proteins of the dental pellicle.
• Some molecules of the pellicle undergo conformational changes when they adsorb to the tooth
surface so that new receptors become available.
• Competitive growth among the predominantly coccoid microbial colonies continues for about 1
week. Filamentous bacteria then begin to penetrate the coccoid plaque from the surface, and it
gradually becomes predominantly filamentous.

33. • The process may continue for about 2 weeks more, the
columnar microbial colonies are replaced by a dense mat
of filamentous bacteria, oriented roughly perpendicular to
the colonized surface.
• 1 to 2 weeks after initiation , the diversity of the flora has
increased to include motile bacteria, spirochetes and
vibrios as well as fusiforms. Attached gingival plaque fills
the gingival sulcus, while the spirochetes and vibrios
move along the apical regions of the sulcus.

34. COLONIZATION AND PLAQUE MATURATION:
• Co aggregation - cell to cell recognition of genetically distinct partner cell types.
(Kolen brander PE etal. 1993)
• When the firmly attached microorganisms start growing and the newly formed bacterial clusters
remain attached, microcolonies or a biofilm can develop. Essentially all oral bacteria possess
surface molecules that foster some type of cell to cell interaction. This process occurs primarily
through the highly specific interaction of protein and carbohydrate molecules located on the
bacterial cell surfaces.

35. • In addition to the less specific interactions resulting from hydrophobic, electrostatic and van
der waals forces. Each new cell becomes itself a nascent surface and therefore may act as a
coaggregation bridge to the next cell type that passes.
• Well characterized interactions of secondary colonizers with early colonizers include the
coaggregation of F. nucleatum with S. sanguis, P. loeschii with A. viscosus.
• Secondary colonizers P. intermedia, Capnocytophaga spp. F. nucleatum, P. gingivalis do not
initially colonize the clean tooth surfaces but adhere to bacteria already in the plaque mass.
• In the latter stages of plaque formation, coaggregation between different gram negative
species is likely to predominate.

36. CORNCOB FORMATION: (Gibbsons & Nygaard)
• Feature of plaque present on teeth associated with gingivitis.
• Rod-shaped bacterial cells eg. Bacterionema matruchotii or
Actinomyces sp. 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.
• Commonly seen in the subgingival plaque of teeth associated with
periodontitis
• Detected between filaments of bacteria to which gram –ve rods
adhere.

38. CONTENTS: (PART- II)
• PROPERTIES OF BIOFILM
• SUPRAGINGIVAL PLAQUE FORMATION
• FACTORS THAT FAVOUR PLAQUE RETENTION
• DE NOVO SUBGINGIVAL PLAQUE FORMATION
• MICROBIAL SPECIFICITY
• HOST SUSCEPTIBILITY
• CONCLUSION

40. PHYSIOLOGICAL HETEROGENEITY
• Cells of the same microbial species can exhibit extremely different
physiological states in a biofilms even though separated by as little as 10µm.
• The use of microelectrodes has shown that pH can vary quite remarkably
over short distances within a biofilm. The number of metal ions can differ
sufficiently in different regions of a biofilm, so that a difference in ion
concentration can produce measurable potential differences.

41. • Authors suggest that antibiotics that kill actively growing cells would
affect the outer layer of the biofilm, but the remaining cells would not be
affected.
• Bacterial cells within biofilms can produce enzymes such as β lactamase
against antibiotics or catalases, superoxide dismutase against oxidizing ions
released by phagocytes. These enzymes release in to matrix, producing an
almost impregnable line of defence. Bacterial cells in biofilms can also
produce elastases and cellulases, which become concentrated in the local
matrix and produce tissue damage.

42. METABOLIC INTERACTION

43. QUORUM SENSING:
• The possible role of quorum sensing in influencing the properties of
biofilms was first suggested by Cooper et al.
• Quorum sensing in bacteria “involves the
regulation of expression of specific genes through
the accumulation of signaling compounds that
mediate intercellular communication”.
(Prosser
1999)

45. ANTIBIOTIC RESISTANCE (Gilbert et al 1997).
• Due to slow rate of growth of bacterial species.
• Resistance of bacteria to antibiotics is affected by their nutritional
status, growth rate, temperature, pH and prior exposure to the
subeffective concentrations of antimicrobial agents.

46. • The matrix performs a “homeostatic function”. The deep cells in the
biofilm experience different conditions such as hydrogen ion
concentration or redox potential than cells at the periphery of the
biofilm or cells growing planktonically.
• In addition, the slower growing bacteria often express non specific
defense mechanism including shock proteins, multi drug efflux
pumps & increased exopolymer synthesis.

47. GENE TRANSFER: (Robert et al 2003):
• Cells also communicate with one another in biofilms via horizontal gene
transfer. (Lie et al, 2002)
• Mainly occurs through –
• Transformation
• Transduction
• Conjugation

48. SUPRAGINGIVAL PLAQUE FORMATION
• Early undisturbed plaque formation on teeth followds an exponential
growth curve.
• During first 24 hrs starting with clean tooth surface plaque growth is
negligible clinically.
• After 4 days: 30% of total coronal tooth area.
• Microbial composition changes with shift towards more anaerobic &
gram negative.
• Growth of older plaque is much slow than in newly formed.

49. FACTORS THAT FAVOUR PLAQUE RETENTION
• Topography of supragingival plaque
• Surface microroughness
• Individual variables that influence plaque formation
• Variation within the dentition
• Impact of gingival inflammation & saliva
• Impact of patient’s age
• Spontaneous tooth cleaning

50. DE NOVO SUBGINGIVAL PLAQUE FORMATION
• One cannot sterilize the periodontal pocket.
• Partial reduction of around 3 logs; 10^8 bacterial cells to 10^5 cells
followed by rapid regrowth towards nearly pre treatment levels within 7
days.
• Introduction of oral implants (two-stage type) provided a new
experimental setup.

52. NON SPECIFIC PLAQUE HYPOTHESIS:• Walter Loesche (1976).
• Periodontal diseases were believed to result from an accumulation of
plaque over time, eventually in conjunction with a diminished host response
and increased host susceptibility with age.
• It states that periodontal disease results from the “elaboration of noxious
products by the entire plaque flora”.
• When only small amounts of plaque are present, the noxious products are
neutralized by the host. Similarly, large amounts of plaque would produce
larger amounts of noxious products, which would essentially overwhelm
the host’s defenses.

53. • Inherent in the non specific plaque hypothesis is the concept that control of
periodontal disease depends on control of the amount of plaque
accumulation.
• The current standard treatment of periodontitis by debridement (non
surgical or surgical) and oral hygiene measures still focuses on the removal
of plaque and its products. Thus, although the non specific plaque
hypothesis has been discarded, much clinical treatment is still based on the
non specific theory.

54. • Contradictions of the non specific plaque hypothesis.
• Some individuals with considerable amounts of plaque and calculus, as
well as gingivitis, never developed destructive periodontitis.
• Individuals who did present with periodontitis demonstrated considerable
site specificity in the pattern of the disease. Some sites where unaffected,
whereas advanced disease was found in adjacent sites. In the presence of a
uniform host response, these findings were inconsistent with the concept
that all plaque was equally pathogenic.

55. SPECIFIC PLAQUE HYPOTHESIS
• It states that only certain plaque is pathogenic, and its pathogenicity
depends on the presence of or increase in specific microorganisms.
(Newman, Socransky; 1977)
• This concept predicts that plaque harboring specific bacterial pathogens
results in a periodontal disease because these organisms produce
substances that mediate the destruction of the host tissues.

56. • The association of specific bacterial species with disease when
microscopic examination of plaque revealed that different bacterial
morphotypes were found in healthy versus periodontally diseased
sites.
• Major advances were made in techniques used to isolate and identify
periodontal microorganisms. Acceptance of the specific plaque
hypothesis was spurred by the recognition of A. actinomycetocomitans
as a pathogen in localized aggressive periodontitis.
• (Slots J: Subgingival microflora of
Advanced periodontitis, 1977)

57. • The theory that some bacteria have a specific role in periodontal
diseases is challenged by:
• Most of the available data are derived from retrospective analysis. The
disease develops before the microbiota are identified.
• Demonstration of association is not a proof of the cause: Microbial
changes may be the consequence, rather than the cause of the disease.

58. ECOLOGICAL PLAQUE HYPOTHESIS: (PD Marsh
1994)
• Unique local environment influences the composition of the oral microflora.
• From an ecological point of view, the oral cavity is an open growth system; that
is nutrients and microbes are repeatedly introduced to and removed from the
system. The flow rate of the saliva is so high that, in order to colonize the surfaces
of the oral cavity, the organisms must be able to adhere or be retained in some other
way.
• Also the flow of the gingival fluid, friction from chewing, oral hygiene procedures
and desquamation of epithelial cells from the mucous membrane, removes the
bacteria from the oral surfaces.

59. • The oral cavity consists of several distinct sites, each of which will support the
growth of a characteristic microbial community, and there are therefore
pronounced differences in the composition of the microbiota on the mucus
membranes, tongue and the teeth and in the gingival sulcus.
• Once established, the microflora at a site remain relatively stable over time,
despite regular minor disturbances in the oral environment. (Marsh, 1989).
• The stability is termed as microbial homeostasis that is not from any metabolic
indifference among the components of the microflora but rather from a dynamic
balance of microbial interactions, including both synergism and antagonism.

61. • The ability to maintain homeostasis within a microbial community
increases with a species diversity. In dental plaque, diversity is enhanced by
the development of food chains among bacterial species and their use of
complementary metabolic strategies for the catabolism of endogenous
nutrients, such as glycoproteins and proteins.
• Antagonism is also a major mechanism in maintaining microbial
homeostasis in plaque. Bacteriocins and bacteriocin like substances are
produced by many genera of oral bacteria
(Marsh, 1989).

62. • Although specific benefit of bacterocins is unclear, their production can confer an
ecological advantage on an organism during colonization. Other inhibitory factors
produced by plaque bacteria include organic acids, hydrogen peroxide and enzymes.
• It was found that subgingival plaque samples from healthy subjects contained
organisms that could inhibit the growth of several periopathogens.
(Hillman and Socransky, 1989).
• In contrast, plaque from sites, with localized aggressive periodontitis or with
refractory periodontitis invariably lacked organisms that produce inhibitors.

63. KEYSTONE PATHOGEN HYPOTHESIS
• George H (2012), Polymicrobial synergy/ Dysbiosis model
• Indicates that certain low abundance microbial pathogens which can
cause an inflammatory disease by remodelling a normal microbiota into a
dysbiotic one.
• Certain pathogens may trigger the disruption of microbial homeostasis
leading to the development of periodontal disease.
• Interspecies communication between keystone pathogens & accessory
pathogens leads to overgrowth of pathogenic microbiota to a dysbiotic
microbial community.

64. HOST SUSCEPTIBILITY
• Determined by
• Genetic
• Environmental
• Behavioral factors
• Viral infections
• Stress, emotional & psychological load.

65. CONCLUSION:
• The oral cavity harbors a diverse, abundant and complex microbial community.
Bacteria accumulate on both hard and soft oral tissues in a sessile biofilm. Under
certain circumstances, however, the oral microbiota can be directly or indirectly
responsible for disease
• The biofilm structure provides a defense against host protective mechanisms as
well as against microbial agents. Organisms growing within biofilms often differ
physiologically from those growing in a planktonic state and physiological
activity differs markedly from one site in a biofilm to another.

66. • The biofim is an effective survival structure that protects the resident
organisms from the exogenous potentially harmful factors and permits
cooperative interactions between cells of the same or different species.
• The microorganisms within the dental plaque biofilm do not exist as
independent organisms , but rather function as a coordinated, spatially
organized and metabolically integrated microbial community.
• (Marsh and Bradshaw 1997).

67. REFERENCES:
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Analysis. High-Throughput 2018.
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