Dental plaque forms through sequential colonization of microorganisms on tooth surfaces. It is made up of bacteria, epithelial cells, and extracellular matrix. Plaque formation involves acquired pellicle formation, reversible bacterial attachment, irreversible attachment through adhesins, microbial succession through coaggregation, and maturation of the biofilm and matrix. The microbial composition of plaque varies by oral site and influences diseases like periodontitis and dental caries. Periodontitis results from an imbalance in homeostasis allowing pathogenic bacteria to overgrow. Dental caries occurs when frequent sugar consumption in plaque favors acid-tolerant bacteria like mutans streptococci, changing the microbiota and predisposing to demineralization.

1. ORAL MICROFLORA –PART 2
By :-Dr PREM SHANKAR CHAUHAN

2. ORAL MICROFLORA – DENTAL IMPLICATIONS (PART II)
◎ DENTAL PLAQUE
◎ FORMATION OF DENTAL PLAQUE
◎ PLAQUE HYPOTHESIS
◎ MICROBIOLOGY OF PERIODONTAL DISEASES
◎ MICROBIOLOGY OF DENTAL CARIES
◎ ENDODONTIS INFECTION

3. DENTAL PLAQUE
◎ Plaque is highly specific and selective but structurally variable clinical entity
characterized by sequential colonization of microorganisms on the surface of teeth,
restoration and other parts of the oral cavity. It is made up of mucins, desquamative
epithelial cells and microorganisms embedded in an extracellular matrix. (WHO)
◎ Dental plaque is defined clinically as a structured, resilient, yellowish grayish substance
that adhere tenaciously to the intra oral hard surfaces, including removable and fixed
restorations. (CARRANZA)

4. MECHANISMS OF DENTAL PLAQUE FORMATION
1. Acquired pellicle formation
2. Transport of microorganisms and reversible attachment
3. Pioneer microbial colonisers and more permanent attachment (adhesin–receptor
interactions)
4. Coaggregation/coadhesion and microbial succession
5. Maturation of the biofilm and matrix formation
6. Detachment from surfaces

6. 2. Transport of microorganisms and reversible attachment
 Microorganisms are generally transported passively to the tooth surface by the flow of saliva;
few oral bacterial species are motile (e.g. possess flagella), and these are mainly located
subgingivally.
 The Derjaguin and Landau and the Verwey and Overbeek (DLVO) theory - the total
interactive energy, VT, of two smooth particles is determined solely by the sum of the van der
Waals attractive energy (VA) and the usually repulsive, electrostatic energy (VR).
 Reversible attachment -Weak, long range, van der Waals forces

7. 3.Pioneer microbial colonizers and irreversible attachment (adhesin–
receptor interactions)
 Within a short time, these weak physicochemical interactions
may become irreversible due to adhesins on the microbial cell
surface becoming involved in specific, short-range
interactions with complementary receptors in the acquired
pellicle.
 Within minutes, coccal bacteria appear on the surface, and
these pioneer organisms are mainly streptococci, especially
members of the mitis-group of streptococci (e.g. S. sanguinis,
S. oralis and S. mitis biovar 1).

9.  Once attached, these pioneer populations start to
divide and form microcolonies; these early
colonizers become embedded in bacterial
extracellular slimes and polysaccharides together
with additional layers of adsorbed salivary proteins
and glycoproteins
 The irreversible attachment of cells to the tooth
involves specific, short range, stereochemical
interactions between components on the microbial
cell sur-face (adhesins) and complementary receptors
in the acquired pellicle.

10. 4. Coaggregation/coadhesion and microbial succession
 Over time, the plaque microflora becomes more diverse; there is a shift
away from the initial preponderance of streptococci to a biofilm with
increasing proportions of Actinomyces and other Gram positive bacilli.
Some organisms that were unable to colonize the pellicle-coated tooth
surfaces are able to attach to already-adherent pioneer species by further
adhesin–receptor interactions (coaggregation/co-adhesion).
 Coaggregation can result in some unusual morphological formations,
e.g. ‘corn-cob’ structures.
 ‘Corn-cobs’ can be formed between streptococci with certain types of
fibrils and C. matruchotii; similar associations occur between
Eubacterium and Veillonella spp..

12. 5. Mature biofilm formation
 The microbial diversity of plaque will increase over time due to successive waves of
microbial succession and subsequent growth. The growth rate of individual bacteria within
plaque slows as the biofilm matures, and the mean doubling times of 1–2 hours observed
during the early stages of plaque formation rise to between 12–15 hours after 1–3 days of bio-
film development.
 some of the adherent bacteria synthesize extracellular polymers (soluble and insoluble
glucans, fructans and heteropolymers) which will make a major contribution to the plaque
matrix.

13.  A matrix is a common feature of all biofilms, and is more than a chemical scaffold to
maintain the shape of the biofilm. It makes a significant contribution to the structural integrity
and general tolerance of biofilms to environmental factors (e.g. desiccation) and antimicrobial
agents. The matrix can be biologically active and retain water, nutrients and enzymes within
the biofilm.
 Such vertical and horizontal stratifications will cause local environmental heterogeneity
resulting in a mosaic of microhabitats or microenvironments. Such het-erogeneity can explain
how organisms with apparently contradictory growth requirements in terms of nutritional,
atmospheric or pH requirements are able to coexist in plaque at the same site.

14. 6. Detachment from surfaces
 Shear forces can remove microorganisms from oral surfaces, but some bacteria can actively
detach themselves from within the biofilm so as to be able to colonize elsewhere.
Streptococcus mutans can synthesize an enzyme that can cleave proteins from its own cell
surface and thereby detach itself from a mono-species biofilm. Similarly, a protease produced
by Prevotella loescheii can hydrolyze its own fimbrial-associated adhesin responsible for
coaggregation with S. oralis as well as binding to fibrin. Bacteria may be able to ‘sense’
adverse changes in environmental conditions, and these may act as cues to induce the genes
involved in active detachment.

15. CONSEQUENCES OF BIOFILM FORMATION
 A biofilm life-style has a direct and indirect impact on gene expression by oral bacteria, with
many biofilm-specific genes being expressed. Cells in biofilms also display a decreased
sensitivity to antimicrobial agents. Microorganisms in biofilms are in close proximity with
one another which facilitates a range of biochemical (antagonistic and synergistic)
interactions, as well as opportunities for gene transfer. In addition, attached cells can
communicate with one another, and coordinate gene expression, via the production of small
diffusible signalling molecules, such as competence-stimulating peptide by S. mutans, and
autoinducer-2 by a range of oral species. The final outcome is the development of a complex,
interactive multi-species, spatially- and functionally- organized biofilm.
◎

17. Enzyme Complementation
◎ Bacterial cooperation in the degradation of host
glycoproteins (enzyme complementation). For
example, organism A is able to cleave the
terminal sugar of the oligosaccharide side- chain,
which enables organism B or D to cleave the
penultimate residue, etc.

18. Food-chain
◎ Establishment of a simple food-chain.
Bacteria such as Streptococcus mutans
produce lactate from fermentable sugars that
can be metabolised to weaker acids by
Veillonella species; in gnotobiotic animals,
this food-chain can reduce the cariogenic
potential of these streptococci.

19. BACTERIAL COMPOSITION OF THE CLIMAX COMMUNITY OF
DENTAL PLAQUE FROM DIFFERENT SITES
◎ The microbial composition of biofilms
on teeth varies at distinct surfaces
because of differences in the local
environment.
◎ Fissures are influenced by the
properties of saliva, and the biofilms
are dominated by streptococci; these
bacteria have a saccharolytic style of
metabolism.
◎ The gingival crevice supports the
growth of fastidious, obligately
anaerobic bacteria, many of which are
Gram-negative and proteolytic. GCF
has a major influence on the biology of
this site.

20. MICROBIAL HOMEOSTASIS IN DENTAL PLAQUE
◎ The balance of the microbiota at a site
remains reasonably stable unless
severely perturbed by an environmental
stress. Such a stable microbiota is also
able to prevent exogenous species from
colonising. This stability (termed
microbial homeostasis) is due, in part,
to a dynamic balance of synergistic
(e.g., coadhesion, the development of
food chains, and metabolic
cooperation) and antagonistic (e.g.,
production of bacteriocins, hydrogen
peroxide, organic acids and a low pH)
microbial interactions. Disease can
occur when homeostasis breaks down.

22. PLAQUE HYPOTHESIS
1. Nonspecific plaque hypothesis (Walter Losche Theliade 1976)
2. Specific plaque hypothesis (Walter Losche 1979)
3. Ecological plaque hypothesis (PD Marsh 1991)

23. Periodontal Disease results from elaboration of noxious products by
the entire plaque flora.
When small amounts of plaque is present ,the noxious products are
neutralized by the host.
Large amount of noxious products, which would essentially
overwhelm the host defenses.
Although this hypothesis is discarded ,but still the treatment is based
on this hypothesis.
NON-SPECIFIC PLAQUE HYPOTHESIS

24. Only certain plaque is pathogenic, and its pathogenicity depends on
the presence of or increase in specific microorganisms.
This predicts that plaque harboring specific bacterial pathogens results
in periodontal disease.
Proven by recognition of A.actinomycetem cominants as a pathogen in
LP.
SPECIFIC PLAQUE HYPOTHESIS

25. According this concept the local environment plays an important
role in the etiology periodontal diseases.
Several researchers consider that pathologic flora occurs as a result
of perturbations in the habitat.
Change in the nutrient status of a pocket or chemical and physical
changes to the habitat are thus considered the primary cause for the
over growth by pathogens.
Eg: Gingival inflammation increases the rate of GCF flow which in
turn provides an favorable environment for bacterial growth
ECOLOGICAL PLAQUE HYPOTHESIS

26. The ecological plaque hypothesis in relation to periodontal disease. Plaque accumulation produces an
inflammatory host response; this causes changes in the local environmental conditions which favour
the growth of proteolytic and anaerobic bacteria, many of which are Gram-negative. The risk of
disease is increased if the host has abnormalities in their host defences, or they have other risk factors
such as tobacco smoking, whereas effective oral hygiene will reduce the likelihood of disease. Disease
could be prevented by not only targeting the putative pathogens, but also by interfering with the factors
driving their selection.

27. MICROBIOLOGY OF PERIODONTAL DISEASES
The main types of periodontal disease are:
◎ GINGIVITIS
◎ CHRONIC PERIODONTITIS
◎ NECROTIZING FORMS OF PERIODONTAL DISEASES
◎ AGGRESSIVE PERIODONTITIS.

28. GINGIVITIS
◎ Chronic marginal gingivitis is a non-specific, reversible inflammatory response to biofilm
accumulation around the gingival margin.

29. CHRONIC PERIODONTITIS
◎ This is the most common form of advanced
periodontal disease affecting the general
population, and is a major cause of tooth loss
after the age of 25 years. It differs from
chronic gingivitis in that in addition to the
gingivae being involved, there is loss of
attachment between the root surface, the
gingivae and the alveolar bone, and bone loss
itself may occur, giving an increased depth on
probing and bleeding. In contrast to gingivitis,
these pathologic changes are irreversible.

32. Aggressive periodontitis is rare, and is associated with functional abnormalities of neutrophils.
Plaque from affected sites is sparse but, in the localised form of the disease, often contains
Aggregatibacter actinomycetemcomitans, strains of which produce a powerful leukotoxin.
◎ Clinically :-12-20 yrs
◎ No/little gingival inflammation
◎ Marked, localized alveolar bone loss perm 1st molar & incisors
Aggressive periodontitis

33. PRE-PUBERTAL PERIODONTITIS
• Clinically- A rare form of periodontal disease occurs during or immediately after the eruption of the
primary teeth.
• Females.
• loss of bone around multiple teeth
• Microbiolgic findings- Fusobacterium, Violinella, Bacteroides & Capnocytophaga commonly found

34. ANUG (ACUTE NECROTIZING ULCERATIVE
GINGIVITIS)
Necrotising ulcerative gingivitis is a painful, condition, which has a
fusospirochaetal aetiology. Culture and molecular studies have
detected a range of Treponema spp. and fusiform bacteria invading
gingival tissues.

35. ◎ Microbiology - Harbour high number of Spirochetes & P.intermedia
◎ Early microscopic examination identified high levels of Fusobacteria (gram
negative rods)

36. interactions between the host defences and the adapting subgingival biofilm during the
development of a periodontal pocket.

38. MICROBIAL FLORA IN PERIODONTAL DISEASE
Health/ Disease Predominant micro-organisms
In Health Mainly Gm+ve cocci (Streptococcus) &
facultative (anaerobic) –Streptococcus, E.coli
org.. Spirochaetes & motile rods < 5%
Chronic Gingivitis 55% Gm+ve & facultative anaerobes- Actinomyces,
Propionibacterium, Lactobacillus, Streptococcus .
45% Gm –ve & anaerobic organisms Prevotella,
porphromonas, fusobacterium, wolinella
Localized Juvenile Specific org. implicated – Actinobacillus
Periodontitis actinomycetemcomitans, Capnocytophaga spp. &
P. gingivalis
ANUG F. nucleatum + Treponema spp.(fusospiro Complex)
Borrella vincenti, bact.melaninogenicus – isolated

39. APPROACHES FOR CONTROLLING PLAQUE-MEDIATED
DISEASES
◎ FLUORIDE
◎ ANTIMICROBIAL AGENTS
◎ SUGAR SUBSTITUTES
◎ REPLACEMENT THERAPY
◎ PREBIOTICS
◎ PROBIOTICS
◎ ACTIVE VACCINATION
◎ PASSIVE VACCINATION
◎ PHOTODYNAMIC THERAPY
◎ NANOTECHNOLOGY
◎ REDOX AGENTS
◎ ANTIINFLAMMATORY AGENTS.

40. DENTAL CARIES
• Dental caries is a infectious microbiologic disease
of the teeth that results in localized dissolution and
destruction of calcified tissues. (STURDEVANT)
• It is defined as localized post eruptive pathological
process of external origin involving softening of
the hard tooth tissue and proceeding to the
formation of cavity. (WHO)
• It is defined it as a ―microbial disease of the
calcified tissues of the teeth, characterized by
demineralization of the inorganic portion and
destruction of the organic substance of the tooth.
(SHAFER)

41. BACTERIA AND DENTAL CARIES
KEYES TRIAD - 1960
NEWBRUN
TETRALOGY - 1982

42. Ecological plaque hypothesis in relation to the aetiology of dental
caries
◎ Frequent metabolism of fermentable sugars in dental plaque produces regular and
prolonged conditions of low pH; this environmental change in plaque favours the growth
of acid-tolerating bacteria (such as mutans streptococci [MS], lactobacilli and
bifidobacteria) at the expense of species associated with sound enamel. Such a change in
the microbiota predisposes a surface to demineralisation. Caries is promoted in individuals
who regularly consume fermentable carbohydrates and/or have an impaired saliva flow,
whereas good oral hygiene and exposure to optimum levels of fluoride would reduce the
risk of demineralisation. Disease could be prevented by not only targeting the putative
pathogens, but also by interfering with the factors driving their selection.

43. The extended ecological caries hypothesis
◎ Environmental
acidification acts as the
main driving force for
acid-induced
adaptation and acid-
induced selection of
the microbial
community as it passes
from the dynamic
stability stage via the
acidogenic stage to the
aciduric stage.
Concurrently, caries
lesion dynamics shift
towards net mineral
loss. The reactions can
be reversed by
elimination of the acid
stress.

44. 1. Rapid transport of dietary sugars:
Mutans streptococci possess more than one
sugar transport system.
2. Rapid rates of glycolysis (acidogenicity):
can result in a terminal pH of below 4.5 in
only a few minutes.
3. Tolerance of, and growth at, low pH
(aciduricity): the growth of many of the
bacteria found on sound enamel (e.g.. Strep.
Sanguis) is inhibited at pH <5.5, whereas
this is optimal for cariogenic species.
PATHOGENIC DETERMINANTS OF CARIOGENIC BACTERIA

45. 4. Extracelluar polysaccharide synthesis (EPS): these polymers help make up the
plaque matrix.
a) Glucosyltransferases (GTF's) convert sucrose to soluble and insoluble glucans,
that help consolidate bacterial attachment.
b) Fructosyltransferases (FTF's) convert sucrose to fructans; these polymers are
labile and can be used by plaque bacteria as an energy source.
5. Intracellular polysaccharide synthesis (IPS): can be used during starvation
conditions and catabolised to acid when dietary sugars are not available.
o mutans streptococci but not lactobacilli produce EPS.

47. ◎ Window of Infectivity is used to describe the time period when children are at
greatest risk for acquiring MS.
◎ MS colonization occurs between 19 – 31 months of age, but has been seen as
early as 10months in some populations/studies.
◎ A second “window” is speculated to occur when permanent first molars
erupts.
WINDOW OF INFECTIVITY OF S. MUTANS

48. FIRST WINDOW OF INFECTIVITY
 In 1993, Page Caufield described first window of infectivity” for MS
Colonization
 Oral bacterial levels of 46 mother-child pairs from infant birth to age 5
were studied to determine the age of acquisition of Mutans Streptococci
 He noted initial acquisition of S.mutans and designated the time period as
“window of infectivity”—7-31 months

49. SECOND WINDOW OF INFECTIVITY
 Krass et al (1967) and Edrman et al (1975) : reported that at 2-6 yrs of age
the child is less susceptible to acquire S.mutans .
 Thus the “2nd window of infectivity” is present in permanent dentition
between 6-12 yrs of age

50. 1. PIT & FISSURE CARIES
◎S.mutans & Lactobacilli
◎Anaerobic rods, Bifidobacterium,
Eubacterium, & Propionbacterium
identified.
◎Actinomyces,& Bacillus species -
invasive front of the deep dentinal lesions

51. 2. SMOOTH SURFACE CARIES
◎most consistent are gram positive facultative
cocci, S.Mutans & S.Salivarius.
◎S.Mutans –primary etiologic agent
◎Role of S.Salivarius in caries production is
not well known

52. 3. NORMAL BUCCAL-LINGUAL SMOOTH SURFACE CARIES
S. mutans group
4. NORMAL INTERPROXIMAL SMOOTH SURFACE CARIES
S. mutans and lactobacilli
5. RAMPANT SMOOTH SURFACE CARIES
S. mutans group

53. 6.ROOT SURFACE LESIONS
◎ High number of Actinomyces species
including A .viscosus, A. naeslundii & A.
odontolyticus.

54. Type of caries Etiological organisms significance in disease
Pit & fissure caries S mutans
S sanguis
Other streptococci
Lactobacillus sp
Actinomyces sp
Very significant
Not very significant
Not very significant
very significant
May be significant
Smooth surface S mutans
S salivarius
Very significant
Probably not significant
Root surface A viscosus
A naeslundi
Othr filamentous rods
S mutans
S sanguis
S salivarius
Very significant
Very significant
Very significant
Significant
May be significant
Probably not significant
Deep dentinal caries Lactobacillus sp
A naeslundi
A viscosus
Othr filamentous rods
S mutans
Very significant
Very significant
Significant
Very significant
May be significant
Localization of the oral flora related to caries

55. ENDODONTIC INFECTIONS
• A large number of bacteria and some fungi can cause
infection in the dental pulp as well as periapical tissues.
• Dental pulp is a unique formative organ with limited capacity
to withstand bacterial, mechanical and chemical attack. When
bacteria enter the pulp it is unusual for the host defenses to
completely eliminate them. Healing is uncommon and necrosis
results
• With pulpal degeneration, antigens collect within the root canal
system and move to the periapical tissues and further
inflammatory responses lead to formation of abscess,
granulomas or cysts.

56. 12
4
Sources of infection
• Infected carious lesion / iatrogenic exposure
• via periodontal tissues through exposed dentinal tubules, lateral accessory canals or apical
foramen.
• By the lymphatic / hematogeneous route i.e anachoresis (localization of transient bacteria
in the blood into an inflamed area, such as a traumatized / inflamed pulp.)
• Traumatic displacement / fracture can also become a route for microbial ingress to the
pulp.
• Once the disease sets in, these tissues can act as source for spreading infection to various
organs of body through blood resulting in septicemia.

57. • Disease occurring secondary to endodontic treatment
include
- Infective endocarditis
- Cavernous sinus thrombosis
- Bacterial myocarditis
- Cerebral abscess
- Various lesions result as sequelae to pulp necrosis such as granulomas,
abscesses, actinomycosis, cellulites, osteomylitis etc.
58

58. Microflora of traumatized but intact teeth
with necrotic pulps
Mainly and predominantly consists of
B.melaninogenicus in association with
other anaerobic bacteria.
Microflora of acute infections of
endodontic origin
Bacteroides in association with
P.endodontalis, gingivalis and Prevotella
intermedius.
59

59. ]
‘flare-up’infections
Microflora of endodontic Obligate Anaerobes Such As
Veillonella
Capnocytophaga
Eiknella Bacteroides
Fusobacterium
Treponema.
endodontic cases are
Microflora on refractory E. faecalis
Candida albicans
Actinomyces israelii
60

60. Microflora of infected and
untreated necrotic pulp
Root canal flora of teeth with
clinically intact crowns but having
necrotic pulps and diseased periapices
is dominated (>90% ) by the obligate
anaerobes.
Fusobacterium
Porphyromonas
Prevotella
Eubacterium
Peptostreptococcus
Endodontic flora in previously root filled
teeth
Actinomyces
Enterococcus, propionibacterium
61

61. 1. Marsh and Martin’s Oral Microbiology- sixth edition
2. Textbook of Microbiology- Anantnarayan
3. Carranza’s clinical periodontology - 9th edition
4. Dental caries –disease and its clinical managenent – Ole Fejerskov and Edwina
5. A.M Kidd Textbook of cariology– Ernest Newbrun
6. Clinical practice of dental hygienist – Esther’s and Wilkin’s – 8th Ed
REFERENCES