1. 1
Dental plaque
Definition:
"It is the soft tenacious material found on the tooth surface and not readily
removed by rinsing with water"……Dawes et al (1963).
1mm3 of dental plaque contains more than 200 million bacteria and some other
mycoplasma. Although there more than 350 species of bacteria in the oral cavity,
only few are able to colonize the newly cleaned tooth surface.
Microbial biofilm:
Microorganisms attached to the surface spatially organized into a threedimensional structure enclosed in a matrix of extracellular materials derived from the
cells themselves and the environment.
The Formation of dental plaque is due to the following:
●The lowering of oral pH level to acidic zones.
●Poor oral hygiene.
●Predominance of carbohydrates in food.
●Increase of ionic concentration, especially in the saliva.
●Increase the concentration of mucine in saliva.
●Increase of epithelium cell concentration in the saliva with a desquamation of
oral mucosa.
Plaque retention and susceptible sites:
1. enamel pits and fissures on the occlusal surfaces of molar& premolar teeth.
Buccal pits of molars & palatal pits of maxillary incisors
2. Proximal enamel smooth surfaces just cervical to the contact area
3. Enamel at the cervical margin of the tooth at the gingival margins ( in case of
gum recession)
4. Margins of the restorations (especially in case of marginal gap or overhang)

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Disclosing substances for dental plaque:
 Solutions
1. Alkaline fuchsin solution 0.2-0.3%.
2. Methylene blue solution 2% .
3. Gentian violet solution 1%.
4. Toluidine blue solution 1%.
5. Hematoxilyn solution followed by eosin solution
 Toothpaste: Placolot, etc.
 Pills : Ceplac, Revelan, Mentadent
Dental plaque could be classified according to its relationship to the gingival
margin.
 Supragingival plaque
 Subginigval plaque.
Formation and structure of the dental plaque:
The development of dental plaque divided into several stages:
1. Pellicle formation
2. Attachment of single bacterial cells (0-4h)
3. Growth of attached bacteria leading to distinct microcolonies (4-24h)
4. Microbial succession and co-aggregation leading to increased species
diversity concomitant with continued growth of microcolonies (1-14 days)
5. Climax community/mature plaque (2weeks or older)
 Plaque formation is a highly dynamic process, where the attachment, growth,
removal and reattachment of bacteria may occur at the same time.
1. Pellicle formation:
It is acellular proteinaceous film
Forms within minutes to hours on the naked tooth surface

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Mainly composed of salivary glycoproteins, phosphoproteins, lipids and traces of
microbial products
2. Microbial colonization:
Bacteria adhere to the surface by specific mechanisms between the molecules
on the microbial cell surface and the pellicle
3. Initial microbial colonization:
Early
colonization
by
pioneer
colonizers;S.sanguis,
S.
oralis,
S.
mitis,Actinomyces and Gram negative bacteria. It is the outcome of a sensitive
interaction between protein adhesions on the surface of the colonizing bacteria
and carbohydrate receptors adsorbed to the tooth surface.
It was thought that mutans streptococci constitute a part in the initial
community. However it was found to comprise 2% or even less of the initial
streptococcal microflora.
4. Microbial succession:
After initial deposition, clones of pioneer bacteria (Streptococcus sanguis)
expands away from the tooth surface forming parallel columns that moves
outwards in long chains of palisading bacteria and separated by uniform narrow
spaces.
After 24-48 hours, continuous plaque is dominated by cocci and few
rods.Thendue to modified habitat and lowered oxygen concentration, plaque is
dominated later on by increasing Gram-positive rods (Actinomyces) and Gramnegative cocci (Neiseris and Veillonella).
5. Mature plaque:
After 5-7 days of plaque deposition, some microorganisms coaggreggate with
other species to form "corn cob" structures, composed of a central filament coated
with spherical organisms.

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Development of dental plaque biofilm
Corn –cob
organization
Effect of plaque ecology:
Ecosystem: is a circumscribed area occupied by a biologic community
Ecologic niche: the special combination of food and shelter
Colonization resistance: when niche saturation by a microorganism
prevents others from colonization same habitat.
Owing to the differences in local environmental conditions, the
plaquemicroflora differs in composition varies in composition at distinct
anatomic sites of the tooth, for example in the fissures, on approximal
surfaces and in the gingival crevices. The resident microflora of a site acts
as a part of the host defenses by preventing colonization by exogenous
often pathogenic) microrganisms. Once established, the microflora at a site

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remains relatively stable over time, despite minor disturbances in the oral
environment.
In dental plaque, the species diversity is enhanced by the development
of food chains between bacterial species and their use of complementary
metabolic strategies for the catabolism of endogenous nutrients as
glycoproteins and proteins. Individual species possess different overlapping
patterns of enzymatic activity, so that certain mixed cultures of oral bacteria
can synergistically degrade the complex host molecule.
In normal healthy circumstances, the oral flora that are
capable of colonizing the teeth are not capable of causing
the disease!
Hypothesis concerning the pathogenicity of plaque:
1. Non-specific plaque hypothesis:
o Assumed that all accumulations of dental plaque are pathogenic.
o Required a therapeutic goal completely eliminating plaque in all patients.

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2. Specific plaque hypothesis:
o Based on the observation that accumulation of plaque is not always
associated with disease, in such case it could be considered a normal
conditions.
o Plaque is only considered pathogenic when signs of disease are
present.
o Treatment is based on elimination of the specific pathogen but not total
plaque elimination.
The goal of therapy is to suppress the cariogenic plaque and replace
them with pathogen –free plaque.
Achieved by mechanical debridement and chemical agents.
The subsequent plaque will be dominated by non-cariogenic bacteria,
with no or little cariogenic potential.
3. Ecological plaque hypothesis (introduced by Marsh, 1991):
o Proposes that a change in a key environmental factor(s) triggers a shift
in balance of the resident plaque microflora and predisposes a site to
disease.
o In case of health, these organisms are weak competitors and are
suppressed by intermicrobial antagonism.
o A major change in the ecosysytem produces disturbance in the stability
of the community
microbial homeostasis break down and major
shifts in the composition of the microflora occurs.

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Frequent consumption of fermentable dietary carbohydrates leads to
increased proportions of MS and lactobacilli. The metabolism of plaque is
changed from heterofermentative pattern into a one which sugars are mainly
converted into lactic acid (lowering pH), thus enhancing deminerelization.
On the other hand, subjects with a conventional low-sugar diet, plaque
microflora is stable and small amounts of acids is produced at main meals, the
process of demineralization and reminerelization would be in equilibrium.

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Strategies for prevention and control of caries based on plaque ecology
hypothesis:
Lowering the pH less than 5 will promote the overgrowth of aciduric
microorganisms (MS and lactobacilli). A treatment strategy is to increase the
plaque pH to establish harmless normal microflora of the tooth surface.
Preventive measures to control dental plaque:
1. Frequent mechanical removal of plaque from the teeth surfaces, limiting the
thickness of re-accumulated plaque and ensures that saliva could dilute and
buffer the formed acids.
2. Reduction of sugar clearance time by reducing the intake of sticky sugarcontaining products.
3. Use of chemicals such as
o chlorhexidineas a non-specific antiplaque effect as well as a specific
effect on MS
o fluoride ions to reduce acid formation by the acidogenic microorganisms
at low pH

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Dental plaque MCQ:
1. At the early stages of dental plaque formation, the acquired pellicle is:
a. A single layer of microorganisms attached to the naked tooth surface
b. Composed of salivary glycoproteins, phosphoproteins, lipids and traces of
microbial products
c. Formed within 24-48 hours after tooth brushing
d. Formed ofS.sanguis, S. oralis, S. mitis, Actinomyces and Gram negative bacteria
adhering to the tooth surface
2. Colonization resistance means:
a. The influence of antimicrobial agents on a certain microbial species
b. When a microorganism develops resistance against a specific antibacterial agent
c. The plaque microbial community resistance against professional plaque control
d. The niche saturation by a microorganism that prevents others from colonization
same habitat
3. Specific plaque hypothesis:
a. Stated that environmental changescould trigger a shift in balance of the resident
plaque microflora and predisposes a site to disease.
b. Based on the observation that accumulation of plaque is not always associated
with disease and could be considered a normal conditions
c. Assumed that all accumulations of dental plaque are pathogenic.
d. Treatment is based on elimination of the specific pathogen by chemical agents
only.
Answer key:
1
2
3
b
d
b

10. 10
Essay question:
"In normal healthy circumstances, the oral flora that are capable of colonizing the teeth are
not capable of causing the disease." Discuss the statement and confirm your answer with
the different hypothesis concerning the pathogenicity of dental plaque