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1. CHHATTISGARH DENTAL COLLEGE & RESEARCH INSTITUTE,
RAJNANDGAON
“DEPARTMENT OF PERIODONTOLOGY”
SEMINAR PRESENTATION
“DENTAL PLAQUE AS AN ORAL BIOFLIM”
Guided By :
Dr. Gopinath M.D.S
Dr.Ramesh M.D.S
Dr.sunaina M.D.S
Presented By :
.

2. CONTENTS
Introduction
Definitions
Structure and Composition
Plaque as a Biofilm
Plaque formation
Growth dynamics
Characteristics of biofilm bacteria
Microbial specificity of periodontal diseases
 References

3. INTRODUCTION
• Gingivitis and periodontitis are caused by microorganisms; i.e., both are
infectious diseases.
• These microorganisms colonize the gingival region of the tooth surfaces,
supragingivally as well as subgingivally, forming dentogingival plaque,
a so – called biofilm.
• In diseased pockets, microorganisms also grow subgingivally, without
attaching to the tooth surfaces and may invade the periodontal tissues.

4. • Although there are more than 400 species of bacteria in the oral cavity, only a
few have the ability to colonize a newly cleaned tooth surface.
• It is estimated that 1 ml of saliva contains about 200 million bacteria but
only 1 mm3 of dental plaque contains the same number of bacteria; i.e., the
density of bacteria is about 1000 times higher in dental plaque than it is in
saliva.

5. HISTORICAL BACKGROUND
 Antonie leeuwenhoek (1632-1723) – first described oral bacteria, related lack of oral
hygiene to an increase in the quantity of these organisms. He also recommended oral
hygiene procedures to keep the gums healthy (use of salt, toothpicks).
Adolph Witzel (1882) – Identified bacteria as cause of periodontal disease.
WD miller (1890) – first true oral microbiologist, periodontal disease was a mixed
infection of non-specific normal oral flora (non-specific plaque theory) persisted largely
unchallenged for almost 6 decades .

6. DEFINITIONS
 Bowen (1976) – structured, resilient, yellow-grayish substance that adheres
tenaciously to the intraoral hard surfaces, including removable
and fixed restorations.
 Lindhe – bacterial aggregations on the teeth or other solid oral structures.
 WHO - Variable but specific structural entity resulting from the colonization
and growth of microorganisms of various species and strains
embedded in an extra cellular matrix.

7. CLASSIFICATION

8. FIG -Plaque bacteria association with tooth surface and periodontal tissues.

9. STRUCTURE AND COMPOSITION
Microscopic structure:
Supragingival plaque:
Stratified organization of a multilayered accumulation of bacteria.
Gm +ve cocci & short rods predominate at the tooth surface. Gm –ve rods, filaments
& spirochetes predominate in outer surface of the mature plaque mass.

10. A) Microcolonies of plaque bacteria
extending perpendicularly away from
tooth surfaces.
B) Developed supragingival plaque
showing overfilamentous nature and
microcolonies extending away from the
tooth surface. Saliva plaque
interface(S) is also seen .

11. Subgingival plaque:
Tooth associated: characterized by gram-positive rods and cocci, including
Streptococcus mitis, S. sanguis, A. viscosus, Actinomyces naeslundii, and Eubacterium
spp
- In deeper parts of pocket filamentous organisms become fewer
- The apical border is separated from the junctional epithelium by a layer of host
leukocytes, and the bacteria show an increased concentration of gram-negative rods

12. Tissue associated :
 Microorganisms are more loosely organized, lack definite intermicrobial matrix.
 Contains primarily gram-negative rods and cocci, as well as large numbers
of filaments, flagellated rods, and spirochetes.
 Predominance of species such as S. oralis, S. intermedius, P. micros,
P. gingivalis, P. intermedia, Bacteroides forsythus, and F. nucleatum
 Host tissue cells may also be found.(wbcs & epithelial cells).

13.  Composition depends on pocket depth –
coronally-filaments
apically – spirochetes, cocci, rods
 Tooth associated: Calculus formation & root caries
 Tissue associated: Tissue destruction

14. Composition
1. Water: 80-85% plaque mass ;
50% intracellular, 35% matrix
2. Cells: primarily bacteria, 1 gm (wet weight)= 1011 bacteria.
Non bacterial: Mycoplasma spp, yeasts, protozoa, viruses.
Host cells : epithelial cells, macrophages & leucocytes.
3. Matrix: Organic
Inorganic
This intercellular matrix is derived from saliva, GCF and bacterial products.

15. Organic constituents :
 Polysaccharides : produced by bacteria & maintains the integrity of the biofilm.
 Proteins (albumin) originating from crevicular fluid
 Glycoproteins : an important component of the pellicle that initially coats
a clean tooth surface and later on incorporated into the developing
plaque mass.
 Lipid Material : consists of debris from the membrane of disrupted bacterial and host
cells and food debris.

16. Inorganic components :
 Calcium & phosphorous
 Trace amounts of other minerals such as 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.

17. The inorganic component of subgingival plaque is derived from crevicular fluid , its
calcification results in calculus formation which is typically dark green or dark
brown in colour proabably due to presence of blood products associated with
subgingival hemorrhage.

18.  The tough extracellular matrix of dental plaque makes it impossible to remove
it by rinsing or the use of sprays.
 Plaque can be differentiated from other deposits that may be found on the tooth
surface such as
Materia alba : soft accumulations of bacteria , food matter, and tissue cells that
lack the organised structure of dental plaque and are easily displaced
with a water spray.
Calculus : hard deposit that forms by mineralisation of the dental plaque and is
generally covered by a layer of unmineralised plaque.

19. PLAQUE AS A BIOFILM
 Biofilms are composed of microbial cells encased within a matrix of extracellular
polymeric substances (EPS) such as proteins , polysaccharides and nucleic acids.
 Bacterias in biofilm are 1000 times more resistant to antimicrobial agents than
their planktonic counter parts.
 Bacterias growing in multispecies biofilm interact closely with neighbouring cells .
 Sometimes these interactions are mutually beneficial when one organism
removes another’s waste products and utilizes them to make energy.

20.  Bacterias also compete with their neighbours by secreting antimicrobial molecules
such as inhibitory peptides (bacteriocins or hydrogen peroxide) .
 Biofilm mode of growth facilitates cell- cell signaling and DNA exchange between
bacteria.
 Biofilms are heterogenous : variations in biofilm structure exist within individual
biofilms and between different types of biofilm.

21. Some features are common to many biofilms:
 They contain microcolonies of bacterial cells.
 Water channels are commonly found which form a primitive circulatory
system by removing waste products and bringing fresh nutrients to the
deeper layers of the film.
 Steep chemical gradient exist such as water and pH and these produce
distinct micro-environment within the biofilm.

22. The architecture of a dental plaque biofilm has many common features with other biofilms.
 Heterogenous in structure .
 Open fluid filled channels running through the plaque mass.
 Nutrients make contact with the sessile (attached) microcolonies by
diffusion from the water channels to the microcolony rather than from
the matrix.
 The bacteria exit and proliferate within the intercellular matrix through
which the channels run.

23.  The matrix confers a specialised environment which distinguishes bacteria
that exist within the biofilm from those that are free floating, the so called
planktonic state in solutions such as saliva or crevicular fluid.
 The biofilm matrix functions as a barrier.
 Substances produced by the bacteria within the biofilm are retained and
concentrated which fosters metabolic interactions among the different bacteria.

24. PLAQUE FORMATION

25. Formation of the Pellicle
 All surfaces of the oral cavity including hard and soft tissues are coated with a
layer of organic material known as acquired pellicle (initial phase of plaque
development).
 Within nanoseconds after a vigorously polishing the teeth, acquired pellicle
covers the tooth surface which is a thin, saliva derived layer.

26.  Pellicle consists of :
 glycoproteins (mucins)
 proline-rich proteins
 phosphoproteins (e.g., statherin)
 histidine-rich proteins
 enzymes (e.g., α-amylase)
 other molecules that can function as
adhesion sites for bacteria (receptors).

27.  Pellicle composed of two layers :
 Basal layer : which is very thin and is very difficult to remove even
with harsh chemical and mechanical treatments.
 Globular layer : thicker layer , upto 1 µm or more, that is easier to
detach.
 The mechanisms involved in enamel pellicle formation include electrostatic, vander
Waals, and hydrophobic forces.
 The specific components of a pellicle also depend on 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.

28.  Characteristics of the underlying hard surface influence initial bacterial
adhesion .
 Many enzymes retain enzymatic activity when incorporated into the pellicle such as
 peroxidases
 lysozyme
 α- amylase
may affect the physiology and metabolism of adhering bacterial cells.

29. Initial Adhesion And Attachment Of Bacteria
 The initial steps of transport and interaction with the surface are non- specific
(i.e. they are same for all bacteria).
 The proteins and carbohydrates that are exposed on the bacterial cell surface become
important once the bacteria are in loose contact with the acquired enamel pellicle.
 It is the specific interactions between microbial cell surface “adhesin” molecules and
in the salivary pellicle that determine whether a bacterial cell will remain associated
with the surface.

30.  Only a small proportion of oral bacteria posses adhesins that interact with receptors in
the host pellicle and these organisms are the most abundant bacteria in biofilms.
 The first 4 to 8 hours , 60 to 80% of bacteria present are members of the genus
Streptococcus.
 Other bacteria commonly present at this time include species that cannot survive without
oxygen ( obligate aerobes) such as Haemophilus spp. and Neisseria spp. As well as
organisms that can grow in the presence or absence of oxygen (facultative anaerobes)
including Actinomyces spp. and Veillonella spp.

31.  These species are considered the “primary colonizers” of tooth surfaces.
Primary colonizers :
 Provide new binding sites for adhesion by other local bacteria.
 The metabolic activity of the bacterias belonging to this group modifies
the local microenvironment that can influence the ability of other bacteria
to survive in the plaque biofilm.
E.g. By removing oxygen , the primary colonizers provide conditions of
low oxygen tension that permit the survival and growth of obligate
anaerobes.

32. The initial steps in colonization of teeth by bacteria are :
3 stages:
1. Phase 1, Transport to the surface
2. Phase 2. Initial adhesion
3. Phase 3. Strong attachment

33. Phase 1 : Transport to the surface .
 Initial transport of the bacterium to the tooth surface occur through
 brownian motion (average displacement of 40 μm/hour)
 sedimentation of microorganisms
 liquid flow
 active bacterial movement (chemotactic activity).

34. Phase 2: Initial adhesion.
 Results in an initial, reversible adhesion of the bacterium.
 Initiated when the bacterial cell comes into close proximity to the surface
(separation distance 50nm).
 Through long-range and short-range forces, including van der Waals attractive
forces and electrostatic repulsive forces initial adhesion occurs.
 The behaviour of bacterial cells was described by DLVO theory of colloid
stability.

35. DLVO Theory :
 The total interaction energy (also called the total Gibbs energy) is the sum of the
attractive forces and the electrostatic repulsion.
 Total Gibbs energy consists of a :
 Secondary minimum (where a reversible binding takes place: 5-20 nm
from the surface).
 Positive maximum (an energy barrier B) to adhesion
 Steep primary minimum (located at <2 nm away from the surface) where
an irreversible adhesion is established.

36.  If a particle reaches the primary minimum (<1 nm from the surface), a group of
short range forces (e.g., hydrogen bonding, ion pair formation, steric interaction)
dominates the adhesive interaction and determines the strength of adhesion.

37. Disadvantage of DLVO Theory :
 Bacteria are not perfect spheres, and many cells possess structures such
as fimbriae that protrude from the cell surface.
 Lewis acid base interactions (hydrophobicity) also influence cell surface
interactions.
 Microbial cell surfaces are not uniformly coated with a negative charge.
There may be regions of the cell surface that are positively charged and
for these areas electrostatic interactions with a negatively charged surface
will tend to be attractive.

38. Phase 3. Strong attachment :
 After initial adhesion, a firm anchorage between bacterium and surface is
established by specific interactions (covalent, ionic, or hydrogen bonding).
 This follows direct contact or bridging true extracellular filamentous appendages
(with length upto 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.

39.  The bonding between bacteria and pellicle is mediated by specific extracellular
proteinaceous components (adhesions) of the organism and complementary
receptors (i.e., proteins, glycoproteins, or polysaccharides) on the surface
(e.g., pellicle) and is species specific.
 Each Streptococcus and Actinomyces strain binds specific salivary molecules.
 Streptococci (especially 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.

40.  Actinomyces species can also function as primary colonizers; for example, A. viscosus
possesses fimbriae that contain adhesins that specifically bind to proline-rich proteins of
the dental pellicle.
 Some molecules from the pellicle (e.g., proline-rich-proteins) evidently undergo a
conformational change when they adsorb to the tooth surface so that new receptors
become available.

41.  A. viscosus recognizes cryptic segments of the proline-rich-proteins, which are only
available in adsorbed molecules.
 This provides a microorganism with a mechanism for efficiently attaching to teeth.
 Such hidden receptors for bacterial adhesins are known as cryptitopes.

42. Colonization and Plaque Maturation
 The primary colonizing bacteria adhered to the tooth surface provide new receptors
for attachment by other bacteria in a process known as “coadhesion”.
 Together with growth of adherent microorganisms , coadhesion leads to the development
of microcolonies and eventually to a mature biofilm..
 Cell-cell adhesion between genetically distinct cells occur which forms “clumps” or
“coaggregates”.
 All oral bacteria possess surface molecules that foster some sort of cell-cell interaction.
 The initial stages of coaggregation or coadhesion are same as the first step involved in
bacterial binding to surfaces.

43.  Bacterial cells come into contact through passive or active transport and bind weakly
through nonspecific hydrophobic, electrostatic and Van der Waal’s forces.
 Strong cell-cell interactions are mediated by physiochemical forces (hydrophobic,
electrostatic and Van der Waal’s) but they are highly specific.
 Fusobacteria coaggregate with all other human oral bacteria, whereas veillonellae spp,
Capnocytophagae spp, and prevotellae spp bind to streptococci and actinomycetes.
 Each newly accreted cell becomes itself a new surface and therefore may act as a
coaggregation bridge to the next potentially accreting cell type that passes by.
 Most coaggregations among strains of different genera are mediated by lectin like adhesins
and can be inhibited by lactose and other galactosides.

45.  An analysis of more than 13,000 plaque samples, 40 subgingival microorganisms using a
DNA-hybridization methodology, defined colorcoded “complexes” of periodontal
microorganisms that tend to be found together in health or disease.
 composition of the different complexes was based on the frequency with which different
clusters of microorganisms were recovered, and the complexes were color-coded for easy
conceptualization .
 The early colonizers are either independent of defined complexes or members of the yellow
(Streptococcus spp.) or purple complexes .
 The microorganisms primarily considered secondary colonizers fell into the green, orange, or
red complexes.

47. GROWTH DYNAMICS
ULTRASTRUCTURAL ASPECTS
 Within the first 24 hours changes in the plaque growth can be detected.
 During the first 2 to 8 hours, the adherent pioneering streptococci saturate
the salivary pellicular binding sites and cover 3%to 30% of the enamel surface.
 Then a short period of rapid growth is observed.
After 1 day, biofilm is formed.
 Microorganisms, packed closely together, form a palisade.

48.  Each crack is filled with one type of microorganism.
 As the bacterial densities approach approximately 2 to 6 million bacteria/mm2 on
the enamel surface, a marked increase in growth rate can be observed to 32
million bacteria/mm.
 Further growth of the plaque mass occurs by the multiplication of already adhering
microorganisms rather than by new colonizers.
 This growth period is independent of subject, surface, tooth, or time but appears to be
dependent on cell density.
 The thickness of the plaque increases slowly with time, increasing to 20 to 30 μm after 3
days.

49. SUPRAGINGIVAL PLAQUE FORMATION
 Early undisturbed plaque formation on teeth follows an exponential growth curve.
 During the first 24 hours, starting from a clean tooth surface, plaque growth is
negligible from a clinical viewpoint (<3%coverage of the vestibular tooth surface,
an amount that is clinically almost undetectable).
 During the following 3 days, plaque growth increases at a rapid rate, then slows
down from that point onward.

50.  After 4 days, on average, 30% of the total tooth crown area will be covered with
plaque.
 Plaque does not increase substantially with time after the fourth day but its
composition changes further, with a shift toward more gram-negative anaerobic flora
including an influx of fusobacteria, filaments, spiral forms, and spirochetes.
 Within the biofilm there is ecologic shift, there is a transition from the early aerobic
environment characterized by gram-positive facultative species to a highly oxygen-
deprived environment in which gram-negative anaerobic microorganisms predominate.

51.  The early increase in plaque mass occurs by the proliferation of bacteria which is
already present, and only to a limited extent from new adhering species.
 During the night, plaque growth rate is reduced by about 50% because supragingival
plaque obtains its nutrients mainly from the saliva and salivary flow is decreased at
night.

52. FACTORS AFFECTING SUPRAGINGIVAL PLAQUE FORMATION
 Topography of Supragingival Plaque.
 Surface Micro roughness.
 Individual Variables Influencing Plaque Formation.
 Variation within the Dentition.
 Impact of Gingival Inflammation.
 Impact of Patient’s Age.
 Spontaneous Tooth Cleaning.

53. Subgingival Plaque Formation
 It is technically impossible to record the dynamics of subgingival plaque formation in an
established dentition because a periodontal pocket cannot be sterilized at present.
 Some early studies, using culturing techniques, examined the changes within the
subgingival microbiota during the first week after mechanical debridement and reported
only partial reduction followed by a fast regrowth to almost pretreatment levels within 7
days.
The rapid recolonization of bacteria occurs subgingival debridement because a high
proportion of treated tooth surfaces (5%-80%) still harbored plaque and calculus after
scaling.

54.  These remaining bacteria were considered the primary source for the subgingival
recolonization.
 Some pathogens penetrate the soft tissues or the dentinal tubules and eventually escape
instrumentation.

55.  In a beagle dog study, Leknes et al. studied the extent of subgingival colonization in
6-mm pockets with smooth or rough root surfaces.
 They observed that smooth surfaces harbored significantly less plaque and concluded
that subgingival irregularities shelter submerged microorganisms by impeding the
cleaning action of the gingival crevicular fluid.
 Biopsies of the soft tissues showed a higher proportion of inflammatory cells in the
junctional epithelium (and the underlying connective tissue) facing the rough
surfaces.
 There are higher rates of attachment loss around teeth with grooves in the root
surface.

56. CHARACTERISTICS OF BIOFILM BACTERIA
 Metabolism of Dental Plaque Bacteria
 Communication Between Biofilm Bacteria
 Biofilms and Antimicrobial Resistance

57.  The early colonizers (e.g., streptococci, Actinomyces species) use oxygen and
lower the redox potential of the environment, which then favors the growth of
anaerobic species.
 Gram-positive species use sugars as an energy source and saliva as a carbon
source.
 The bacteria that predominate in mature plaque are anaerobic and asaccharolytic
and use amino acids and small peptides as energy sources.
 The host also functions as an important source of nutrients.
Metabolism of Dental Plaque Bacteria

58. Metabolic interactions among different bacterial species found in plaque , and between the
host and plaque bacteria. These interactions are likely to be important for the survival of
bacteria in the periodontal environment.

59.  Physiologic interactions occur both between different microorganisms in plaque
and between the host and plaque microorganisms.
 These nutritional interdependencies are important for the growth and survival
of microorganisms in dental plaque.

60. Communication Between Biofilm Bacteria
 In a biofilm the bacterias have the capacity to communicate with each other
through “Quoroum Sensing”.
Quoroum Sensing
 Bacterias secrete a signaling molecule that accumulates in the local environment
and triggers a response such as a change in the expression of specific gene once they
reach a critical threshold level.
 The threshold concentration is reached only at high cell density so the bacteria sense
that the population has reached a critical mass or quorum.

61.  Two types of signaling molecules have been detected from the dental plaque
bacteria:
• Peptides released by gram positive organisms during growth.
• Autoinducer- 2 (AI-2) “Universal” signal molecule.
 Peptide signals are produced by oral streptococci and are recognized by cells
of the same strain that produced them.
 Responses are induced only a threshold concentration of the peptide is attained.
 The streptococcal peptides are known as competence stimulating peptides.
 Since the major response to these signals is the induction of competence , a
physiologic state where cells are primed for DNA uptake and incorporation.

62.  In some species, such as S. mutans a small proportion of the cells in a population
respond to competence stimulating peptides by lysing which helps to disseminate
genetic information throughout the population of S. mutans cells.
AI- 2:
 Produced and detected by many bacteria.
 It plays a role in mutualistic interactions between S. oralis and A. oris.
 Interbacterial communication is important for the development of dental plaque.

63. Therefore Quorum Sensing :
 Modulates the expression of genes for antibiotic resistance
 Encourage the growth of beneficial species to the biofilm
 Discouraging the growth of competitors.

64. Biofilms and Antimicrobial Resistance
 The resistance of bacteria to antimicrobial agents is increased in the biofilm.
 Organisms in biofilm are 1000 to 1500 times more resistant to antibiotics
than their planktonic state.
 The mechanism of this resistance differ from
Species to species
Antibiotic to antibiotic
For biofilm growing in different habitats.

65.  Slower rate of growth of bacterial species in a biofilm, makes them less
susceptible to many but not all antiobiotics.
 Although biofilm matrix is not a significant physical barrier to the diffusion of
antibiotics but it has certain properties that can retard antibiotic penetration.
E.g. Strongly charged or chemically highly reactive agents can
fail to reach the deeper zones of biofilm because the biofilm acts as an ion-
exchange resin removing such molecules from solution.

66.  Extracellular enzymes such as β- lactamases, formaldehyde lyase, formaldehyde
dehydrogenase may become trapped and concentrated in the extracellular matrix
which can inactivate some antibiotics (especially positively charged hydrophilic
antibiotics).
 Some antibiotics such as macrolides which are positively charged but hydrophobic are
unaffected by this process.
 Recently “super resistant” bacteria were identified within a biofilm .
 These cells have multidrug resistance pumps that can extrude antimicrobial agents
from the cell.
 Antibiotic resistance may be spread through a biofilm by intercellular exchange of
DNA.

67. BACTERIAL TRANSMISSION AND TRANSLOCATION
 Transmission of pathogens from one locus to another is an important
aspect of infectious disease.
 Such transmission may jeoparadise the outcome of periodontal therapy.
 Molecular fingerprinting techniques illustrated that periodontal pathogens
are transmissible within members of the family.
 Asikainen and co workers used a genetic fingerprinting method to
genotype A.actionomycetemcomitans and they found there is transmission
of this microorganism.

68. MICROBIOLOGIC SPECIFICITY OF
PERIODONTAL DISEASES
 Nonspecific Plaque Hypothesis
 Specific Plaque Hypothesis
 Ecology Plaque Hypothesis
The Keystone Pathogen Hypothesis

69. Nonspecific Plaque Hypothesis :
 According to this theory, 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.
 Large amounts of plaque would produce large amounts of noxious products,
which would essentially overwhelm the host’s defenses.
 Control of periodontal disease depends on control of the amount of plaque
accumulation.

70.  Several observations contradicted the conclusions of the nonspecific 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 disease. Some sites were unaffected, whereas
advanced disease was found in adjacent sites.
 All plaque was equally pathogenic.
Concludes that control of periodontal diseases depends on control of amount of plaque
accumulation
This hypothesis has been discarded still more clinical treatment(eg surgical debridement )
has been based on this hypothesis.

71. Specific Plaque Hypothesis
 States that only certain plaque is pathogenic, and its pathogenicity depends on the
presence of or increase in specific microorganisms.
 Plaque harboring specific bacterial pathogens results in a periodontal disease because
these organisms produce substances that mediate the destruction of host tissues.
 The association of specific bacterial species with disease originated in the early 1960s.
 Microscopic examination of plaque revealed that different bacterial morphotypes were
found in healthy versus periodontally diseased sites.

72.  Disease associated studies shows that periodontal disease can occur even in the
absence of defined pathogens(such as red complex ) and pathogens may be
present in the absence of disease.

73. Ecologic Plaque Hypothesis
 In 1990’s Marsh and co- workers developed this theory.
 Both the total amount of dental plaque and the specific microbial composition
of plaque may contribute to the transition from health to disease.
 The health associated dental plaque is considered to be stable overtime and it
is in a state of dynamic equilibrium or “microbial homeostasis”.
 Host controls subgingival plaque to some extent by a tempered immune response and
low levels of GCF flow.

74.  Changes in the host response may occur by
Excessive accumulation of dental plaque
Plaque independent host factors like
Onset of an immune disorder
Changes in hormonal balance such as pregnancy
Environmental factors like smoking, diet.
 Changes in the host status such as inflammation, tissue destruction or a high GCF flow
lead to a shift in the microbial population in plaque that causes periodontal disease.

75.  Disease associated organisms are minor components of the oral microflora in health
and these organisms are kept in check by interspecies competition during microbial
homeostasis.
 Disease is caused by overgrowth of specific elements of dental plaque when the local
environment changes.

76.  So eliminating the disease inducing stimulus whether it is microbial,
host or environmental will help to restore microbial homeostasis.
 Targeting specific microorganisms may be less effective since the conditions
for disease will remain.

77. The Keystone Pathogen Hypothesis
 The “keystone pathogen” hypothesis holds that certain low-abundance microbial pathogens can
orchestrate inflammatory disease by remodelling a normally benign microbiota into a dysbiotic one.
 Keystone microorganisms that support and stabilize a microbiota associated with disease states are
referred as “keystone pathogens”.
 Three species which comprise the “red complex”, are frequently isolated together, and are strongly
associated with diseased sites in the mouth: P.gingivalis ,T. denticola and T.forsythia .
 P. gingivalis has evolved sophisticated strategies to evade or subvert components of the host
immune system .P.gingivalis impairs innate immunity in ways that alter the growth and
development of the entire biofilm, triggering a destructive change in the normally homeostatic host-
microbial interplay in the periodontium. In other words, P. gingivalis could be a keystone pathogen
of the disease provoking periodontal microbiota.

78. Corruption of complement system
P.Gingivalis gingipains inhibit the classical, lectin and alternate pathways of complement
activation by degrading central complement component c3.
 Gingipains exhibit C5 covertase like activity which generate high level at C5a locally to
activate C5a receptor on leucocytes.
 C5aR signalling is involved in cross talk with TLR2 leading to enhanced inflammation &
impaired leukocyte killing .
 P.gingivalis can also inhibit the synthesis of IL-8 by epithelial cells to delay the recruitment of
neutrophils and facilitate its initial colonization of the periodontium.

79. Complicating Factors
 Periodontitis is considered a mixed infection.
 Recent microbiologic tests clearly indicate that the presence of periodontal
pathogens by itself is not sufficient for the development of periodontitis.
 Because of the high sensitivity of these tests, several pathogens have been
detected in periodontitis-free patients.
 Thus the presence of pathogens is not sufficient for disease and the
amount of pathogens plays the key role in relation to disease.

80.  These observations have major clinical implications :
 Even though a microbiologic analysis is positive, the patient can
be without disease.
 The threshold level for periopathogens between health and disease
is unknown.
 For several species, large intrastrain variations in genetic
information have been detected so information on the genotype
level is needed before the pathogenicity of the strain can be
estimated.

81.  Whether the periopathogens are indigenous species or exogenous, since the
newer techniques have reported high detection frequencies of all pathogens in
healthy subjects as well. This again has significant impact on the treatment
strategies. For indigenous species, the endpoint of a therapy is reduction of the
species, whereas for exogenous species, the endpoint is eradication and prevention
of reinfection.

82.  It is impossible to alter the susceptibility of the host so periodontal therapy
must based on the reduction or elimination of the periodontopathogens in
combination with the reestablishment of a suitable environment (less
anaerobic) for a more beneficial microbiota.
 Because several species might be involved , the use of antimicrobials is extremely
difficult since not all periodontopathogens are susceptible to the same antibiotic.

83. Criteria for Identification of Periodontal Pathogens
 In the 1870s, Robert Koch developed the classic criteria by which a
microorganism can be judged to be a causative agent in human infections.
These criteria, known as Koch’s postulates.
1. Must be routinely isolated from diseased individuals.
2. Must be grown in pure culture in the laboratory.
3. Must produce a similar disease when inoculated into
susceptible laboratory animals.
4. Must be recovered from lesions in a diseased laboratory
animal.

84. Three primary problems are
(1) the inability to culture all the organisms that have been
associated with disease (e.g., many of the oral spirochetes)
(2) the difficulties inherent in defining and culturing sites of
active disease.
(3) the lack of a good animal model system for the study of
periodontitis.

85.  Sigmund Socransky proposed criteria by which periodontal microorganisms
may be judged to be potential pathogens. A potential pathogen:
1) Must be associated with disease, as evident by increase number of organisms at
diseased sites.
2) Must be eliminated or decreased in sites that demonstrate clinical resolution of
disease with treatment.
3) Must demonstrate a host response, in the form of an alteration in the host
cellular or humoral immune response.
4) Must be capable of causing disease in experimental animal models.
5) Must demonstrate virulence factors responsible for enabling the microorganism to
cause destruction of the periodontal tissues.

86. Indigenous microbiome plays a role in maintaining
oral health.
 As Homo sapiens evolved, microorganisms co-evolved with their host to an extent that the human
body is considered a super-organism consisting of functionally, metabolically, and spatially
integrated bacterial and human cells.
 The oral cavity is a unique environment in that it is divided into several smaller habitats—biotic
habitats such as the non-keratinized buccal mucosa, the keratinized mucosa of the tongue and
gingiva, the subgingival sulcus, and abiotic surfaces such as the enamel, dental restorations, and
dental implants.
 A central characteristic of an ecosystem is habitat-specific colonization.
 Evidence is emerging from microbial ecological systems that habitat specificity also allows a
species to regulate gene expression and modify its phenotype to segregate its niche.
 A resident microbial community offers resistance to invasion to the host.

87.  Disruption of resident communities with antibiotics is consistently associated with increased
colonization by pathogenic species or pathologic overgrowth of certain commensals, leading
to disease.
 Loss of colonization resistance can lead to take-over of the community not only by pathogenic
bacteria.
 Evidence has been emerging since then to indicate that species abundance plays a very
important role, in some instances, a greater role than that of species-richness.
 There is evidence that bacterial composition remains stable over long periods of time , even
following routine dental prophylaxis and recolonization.
 Recent evidence suggests the human microbiome is also capable of directly stimulating
various components of the innate and adaptive immune responses.
 Contributions of bacteria to developing TLRs - TLRs respond to both commensals and
pathogens, but evidence now suggests TLRs interaction with commensals contributes to oral
epithelial homeostasis and protection from injury.
 Bacteria and neutrophil function - The normal microbiota has been shown to induce IL-8 ,
presumably to recruit neutrophils to a potential pathogen colonization site to help prevent
overgrowth of pathogens.

88.  Bacteria and regulatory T cell education – commensal Bacteroides fragilis, directs Treg cell
education using the immunomodulatory molecule, polysaccharide A. PSA induces an IL-10
response in T cells that inhibits Th17 expansion preventing future mucosal damage .

89. REFERENCES
• Carranza’s Clinical Periodontology, 10th Edition.
• Carranza’s Clinical Periodontology, 11th Edition.
• Lindhe’s Clinical Periodontology & Implant Dentistry, 5th Edition.
Purnima S. Kumar and Matthew R. Mason. Mouthguards: does the indigenous
microbiome play a role in maintaining
oral health? Front cell infect microbiol 2015 May 6;5:35.
George Hajishengallis, Richard P. Darveau and Michael A. Curtis. The Keystone
Pathogen Hypothesis Nat Rev Microbiol. 2012 October ; 10(10): 717–725.