Anestesia

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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