Dental plaque (also called as microbial
plaque, dental plaque biofilm) is a dense,
nonmineralized, highly organized complex mass
of bacterial colonies in a gel-like intermicrobial
The matrix protects the bacteria from the
defensive cells of the body (neutrophils,
macrophages, and lymphocytes).
It adheres firmly to the acquired pellicle and
also to the teeth, calculus, and restorations.
Acquired pellicle is an amorphous layer that
forms over exposed tooth surfaces, as well as
over restorations and dental calculus.
It begins to form within minutes after all external
material has been removed from the tooth
surfaces with an abrasive.
Although, pellicle performs a protective
function, acting as a barrier to the acids, it also
serves the initial site of attachment to the
bacteria and begins the first stage of biofilm
A biofilm community comprises
a. bacterial microcolonies,
b. an extracellular slime layer,
c. fluid channels, and
d. a primitive communication system.
As the bacteria attach to a surface and to each
other, they cluster together to form sessile,
mushroom-shaped microcolonies that are
attached to the surface at a narrow base
Each microcolony is a tiny, independent community
containing thousands of compatible bacteria.
Different microcolonies may contain different
combinations of bacterial species.
a. Bacteria in the center of a microcolony may live in a strict
b. while other bacteria at the edges of the fluid channels
may live in an aerobic environment.
Thus, the biofilm structure provides a range of customized
living environments (with differing pHs, nutrient
availability, and oxygen concentrations) within which
bacteria with different physiological needs can survive.
The extracellular slime layer is a protective barrier that
surrounds the mushroom shaped bacterial microcolonies
The slime layer protects the bacterial microcolonies
b. antimicrobials, and
c. host defense mechanisms.
A series of fluid channels penetrates the extracellular
These fluid channels
a. provide nutrients and oxygen for the bacterial
b. facilitate movement of bacterial metabolites, waste
products, and enzymes within the biofilm structure.
Each bacterial microcolony uses chemical signals to
create a primitive communication system used to
communicate with other bacterial microcolonies.
Clinically, plaque presents as a transparent film
and therefore, difficult to visualize.
It can be detected with an explorer by passing
the explorer over the tooth surface near the
gingival margin to collect plaque, which makes it
easier to see.
Plaque disclosing solutions that stains the
invisible plaque is used for easy detection of
It stains the plaque and makes it visible to the
eyes. These solutions disclose the extent and
FORMATION OF DENTAL PLAQUE
Dental bacterial plaque is a biofilm that adheres
tenaciously to tooth surfaces, restorations, and
The pattern of plaque biofilm development can be
divided into three phases [Figs 25.3A to C]:
1. Attachment of bacteria to a solid surface;
2. Formation of microcolonies on the surface;
3. Formation of the mature, subgingival plaque
The initial attachment of bacteria begins with
The pellicle is a thin coating of salivary proteins
that attaches to the tooth surface within minutes
This layer is thin, smooth colorless and
translucent and is called as acquired salivary
pellicle. Initially pellicle is bacteria free.
The function of salivary pellicle is mainly
The pellicle acts like double sided adhesive
a. adhering to the tooth surface on one side and
b. on the other side, providing a sticky surface
facilitating bacterial attachment to the tooth
Following pellicle formation, bacteria begin to
attach to the outer surface of the pellicle.
Accumulation is greatest in sites which are
protected from functional friction and tongue
Bacteria connect to the pellicle and each other with
hundreds of hair-like structures called fimbriae.
Once they stick, the bacteria begin producing
substances that stimulate other free floating bacteria to
join the community.
Within the first two days in which no further cleaning is
undertaken, the tooth’s surface is colonized
predominantly by gram-positive facultative cocci,
which are primarily streptococci species.
It appears that the act of attaching to a solid surface
stimulates the bacteria to excrete an extracellular slime
layer that helps to anchor them to the surface and
provides protection for the attached bacteria.
Within first few hours species of Streptococcus and
a little later Actinomyces attach to the pellicle and
Formation of Microcolonies
Microcolony formation begins once the surface of the
tooth has been covered with attached bacteria.
The biofilm grows primarily through cell division of the
adherent bacteria, rather than through the attachment
of new bacteria.
Next, the proliferating bacteria begin to grow away
from the tooth.
Plaque doubling times are rapid in early development
and slower in more mature biofilms.
Bacterial blooms are periods when specific species or
groups of species grow at rapidly accelerated rates.
A second wave of bacterial colonizers adheres to
bacteria that are already attached to the pellicle.
Coaggregation is the ability of new bacterial
colonizers to adhere to the previously attached
The bacteria cluster together to form sessile,
mushroom-shaped microcolonies that are attached
to the tooth surface at a narrow base.
The result of coaggregation is the formation of a
complex array of different bacteria linked to one
Supragingival plaque formation is also pioneered
by bacteria with an ability to form extracellular
polysaccharides which allow them to adhere to
the tooth and each other and these include
a. Streptococcus mitior,
b. S. sanguis,
c. Actinomyces viscosus and
d. A. naeslundii
Plaque grows by both internal multiplication and
Internal multiplication slows considerably as the
Following a few days of undisturbed plaque
formation, the gingival margin becomes inflamed
These inflammatory changes result in the
creation of a deepened gingival sulcus.
The biofilm extends into this subgingival region
and flourishes in this protected environment,
resulting in the formation of a mature subgingival
Gingival inflammation does not appear until the
biofilm changes from one composed largely of
gram-positive bacteria to one containing gram-
A subgingival bacterial microcolony,
predominantly composed of gram-negative
anaerobic bacteria, becomes established in the
gingival sulcus between 3 and 12 weeks after the
beginning of supragingival plaque formation.
Most bacterial species currently suspected of
being periodontal pathogens are anaerobic,
Structure and Composition
Dental plaque can be broadly classified as
supragingival or subgingival.
Supragingival plaque is found at or above the
gingival margin and may be in direct contact
with the gingival margin.
Subgingival plaque is found below the gingival
margins, between the tooth and the gingival
Approximately 70 to 80 percent of plaque is
microbial and the rest represents extracellular
matrix. The intracellular matrix which accounts for
about 20 percent of plaque mass consists of
organic and inorganic materials derived from
saliva, gingival crevicular fluid and bacterial
Organic constituents of the matrix include
polysaccharides, proteins, glycoproteins, and
The most common carbohydrate produced by
bacteria is dextran.
The principal inorganic components are calcium,
phosphorus, sodium, potassium, fluoride and
some traces of magnesium.
Calcium ions may aid adhesion between bacteria
and between bacteria and the pellicle.
The source of both the organic and inorganic
components is primarily saliva and as the
mineral content increases, the plaque may be
calcified to form calculus.
SUPRA AND SUBGINGIVAL
It can be defined as the community of
microorganisms that develops on the tooth
surface coronal to the gingival margin (at or
above the gingival margin).
When it is in direct contact with the gingival
margin it is termed as the marginal plaque.
It can be defined as the community of
microorganisms that develops on tooth surfaces
apical to the gingival margin (found below the
gingival margin, between the tooth and the
gingival pocket epithelium).
Generally, the subgingival microbiota differs in
composition from supragingival plaque mainly
because of the local availability of blood products
and low oxygen potential which characterizes the
Plaque Retention Factors
These are conditions that favor plaque accumulation
and hinder plaque removal by the patient and the
Examples of these are:
• Orthodontic appliances
• Partial dentures
• Faulty restorations
• Deep pockets
• Mouth breathing
• Tobacco use
• Certain medications
Plaque encourages caries formation
1. Enabling bacteria to stick to the teeth.
2. Allowing acids to accumulate around the teeth.
3. Preventing the saliva from reaching the teeth
surface, so stopping it from washing them and
neutralizing the acid.
4. Providing the cariogenic bacteria with a reserve
energy supply, i.e.
SIGNIFICANCE OF DENTAL
The role of dental plaque in the initiation of dental
caries and periodontal infections is now well
Dental caries and periodontal disease result from
the bacterial products of the plaque flora.
Calculus and its Relationship with
• Calculus is formed by the deposition of calcium
and phosphate salts in bacterial plaque. These
salts are present in salivary and crevicular fluids.
• Plaque mineralization begins within 24 to 72
hours and takes an average of 12 days to mature.
• Calculus contributes to the disease by providing
for plaque accumulation. It is not the causative or
etiologic factor, plaque is.
• Calculus is porous and can act as a reservoir or
nidus of bacteria and endotoxin related to the