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6 Dental Plaque and Calculus: Microbial Biofilms and
periodontal Diseases
M. Robert Wirthlin, Jr.
Gary C. Armitage
CLINICAL FEATURES
Dental plaques are complex microbial Communities That form on virtually all surfaces
of the teeth exposed to the bacteria-laden fluids of the mouth. Dental plaques are of
Importance significant clinical Because They are the primary etiologic agents in the
development of dental and periodontal caries1,2 diseases.3,4
Supragingival and Subgingival Plaques
The eruption of teeth into the edentulous mouth of an infant results in the
appearance of two unique agricultural ecosystems of the oral cavity: portions of the teeth
exposed to the environment supragingival and subgingival portions exposed to the
environment of the gingival crevice. Supragingival plaque can be defined as the
That DEVELOPS community of microorganisms on tooth surfaces coronal to the
gingival margin. Important ecologic determinants in the supragingival environment
That have major effects on the development of supragingival plaque are the many
components of whole saliva, and all of the dynamic variables Associated With the
dietary intake of foods and liquids. Subgingival plaque can be defined as the
That DEVELOPS community of microorganisms on tooth surfaces apical to the gingival
margin. Before the development of gingivitis, the dimensions of the subgingival
ecosystem are quite small Because the gingival crevice May only be a few
millimeters deep. With the onset of gingivitis and Its progression to periodontitis,
there is a considerable growth in size of the subgingival compartment. Important
ecologic determinants in the subgingival environment have major effects on That the
development of subgingival plaque are the many components of gingival crevicular
fluid (GCF, eg, antibodies, complement, serum proteins, neutrophils) That
accumulate in the subgingival area as a manifestation of the host's response to the
Presence of bacteria. In the supragingival and subgingival Both environments
interactions and competition Among different species of bacteria Also have a
profound effect on the microbial composition of dental plaque.
Figure 6-1.
Thin supragingival dental plaque of a 32-year-old man who brushed Had not His
teeth for 7 days. A, Unstained plaque is not Readily apparent. B, Extent of the
When Becomes apparent plaque stained with a disclosing solution (ie,
erythrosine dye [FD & C red no. 3]).
The clinical appearance of supragingival plaque is highly variable. It can it appears as
Nearly Invisible to thin film on the tooth surface (Fig. 6-1) to thick mats of materials
That completely obscure the tooth surface and the gingival margin cover (Fig. 6-2).
Most of the plaque mass is Composed of a myriad of microbial clusters surrounded
by an adherent matrix of polysaccharides and glycoproteins produced by bacteria
Within the plaque (Fig. 6-3 and Fig. 6-4). Dental plaque is Not Easily dislodged with
a water spray or vigorous rinsing. In some patients with poor oral Particularly
hygiene, an amorphous materials Composed of bacteria, food particles, debris from
desquamated epithelial cells, and neutrophils collects on the surface of
supragingival plaque. This is loosely adherent debris field: sometimes called alba
Usually and can be washed away by vigorously rinsing or flushing the area with
water. The underlying dental plaque, however I, Remains in place.
Subgingival dental plaque is Difficult to visualize in clinical Situations Because it is
hidden from view Within the gingival crevice or periodontal pocket. However, in
many cases, it is visible to the unaided eye on Extracted teeth. As is the case with
supragingival plaque, electron microscopic examination of subgingival plaque
Clearly Shows That It is Composed of highly Organized masses of bacteria. Many
different morphotypes of bacteria are present in subgingival plaque at Sites with
chronic periodontitis.
Figure 6-2.
Thick supragingival plaque in a 28-year-old man who did not practice oral
Procedures hygiene at all over several years.
Figure 6-3.
Supragingival plaque on the enamel of a tooth with chronic periodontitis. at this
site there was a dense, filamentous bacterial Predominantly mass adherent to the
enamel. E, Enamel space. Original magnification × 850 (Modified from
Listgarten M: Structure of the Microbial Flora Associated with periodontal
health and disease in man. A light and electron microscopic study, J
Periodontol 47: 1-18, 1976)
DENTAL PLAQUES ON THE TEETH AS BIOFILMS
Natural Biofilms are communal aggregations of microorganisms That May form on a
wide range of surfaces. They can Develop at air-liquid interfaces: such as plankton on
on the sea surface or algae scum on a mill pond. Also There are many liquid-solid
surface biofilms: such as slimes on rocks in creeks and Microbial Communities That
cause fouling of dental unit Waterlines. Supragingival and subgingival dental plaques
are classic examples of liquid-solid surface biofilms.5 Other microbial biofilms of
Those include medical Importance form on mucous membranes That, external surfaces
of the eye, artificial heart valves, prosthetic joints contaminated, arteriovenous shunts,
endotracheal tubes, dental implants, and indwelling catheters. In Addition, biofilms
are Involved in persistent infections of bone (eg, osteomyelitis), the biliary tract,
prostate (eg, bacterial prostatitis), and lungs (eg, cystic fibrosis pneumonia) .6
Figure 6-4.
Electron micrograph showing bacteria of supragingival plaque and Their
polysaccharide and glycoprotein matrix surrounding. Original magnification
× 13,750.
Features of Biofilms
Biofilms have several interesting features to protect and serve That Enhance the
Opportunities for nutritional That lies Within the bacteria them. biofilms offer
protection for resident bacteria by giving them a competitive advantage over freefloating
(planktonic) bacteria (Fig. 6-5). Microorganisms of biofilms produced
That called the glycocalyx matrix encloses the microbial community and Protects it
Potentially harmful effects from the surrounding environment of the. Many bacteria
in the state of sessile biofilm to synthesize extracellular polysaccharides That are
Generally Composed of neutral sugars, amino acids, and some uronic acids.
Streptococci high molecular weight dextrans make from glucose and from levans
Gram-negative bacteria fructose.7 make acetylated polymers of uronic acids called
That precipitate alginates When exposed to Ca2 + in saliva.8 These slimy coatings
keep the bacteria banded together and Retain them on the surface, so they 'are not
flushed away by the turbulent action of surrounding fluids (eg, saliva in the case of
supragingival dental plaque biofilms). In Addition, the extracellular polysaccharides
Usually of the glycocalyx are of a high molecular weight and are thereby insoluble.
Consequently, biofilms are Difficult to remove. Indeed, Often Their removal can only
Achieved by Means be mechanical (eg, in the case of dental plaque biofilms by
using a toothbrush and dental floss). The necessity for mechanical removal Also
Applies to many other biofilms of medical Importance: such as biofilm-contaminated
That artificial joints require surgical removal Often for adequate treatment.9 The
matrix of biofilms Also Protects bacteria from the effects of antibiotics and
Because agents in Original antiseptics can not penetrate the barrier Easily provided by the
polysaccharide matrix.6,10-12
Figure 6-5.
Four Important features of biofilms are Their Ability to trap nutrients (A), engage
primary production in the nourishment of Their Own (B), form a digestive
consortium (C), and protect from bacteria in the biofilm or antibacterial agents
phagocytes (D). (Redrawn from Costerton JW, Cheng KJ, Geesey GG, et al:
Bacterial biofilms in nature and disease, Annu Rev Microbiol 41: 435-464,
1987)
In Addition To Its function as a protective barrier, the polysaccharide matrix imparts
Communities to biofilm structure. Although some biofilms are more highly
structured than others, all of them have definite architectural features. For example,
in all biofilms, microorganisms are not uniformly distributed THROUGHOUT the
biofilm. Instead, there are aggregates of microcolonies With Different shapes and
THROUGHOUT sizes dispersed the biofilm. The arrangement of microcolonies Within
biofilms is partly dependent on the external shear forces from the surrounding
environment on the entire biofilm.13
The biofilm May start as a patch on the surface, but as it spreads and it can DEVELOPS
take on the form of mushroom-like pillars or columns; Between channels thereby
the pillars improve increase the circulation of nutrients and discharge of wastes and
toxins.14,15 In a severely starved
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