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Colonization of microenvironments
29-03-2010
Colonization of microenvironments The oral cavity consists of several major and minor compartments, each constituting a separate microenvironment not easily affected by major events in the oral cavity. Examples of major compartments are the tongue, the oral mucosa, and the tonsils. The different approximal tooth surfaces, occlusal fissures, and gingival sulci are regarded as minor compartments. A specific area that supports a bacterial flora is termed a habitat. The flora of a habitat develops through a series of stages, collectively called colonization. Colonization is a complex process, because it involves not only interaction between bacteria and their environment but also interactions among different bacteria. The first important prerequisite for colonization is access. The organisms must be able to enter the habitat and consequently they must be able to be transmitted from one habitat to another. For example, mothers can serve as reservoirs for oral bacteria, which they transmit to their children. Within a single host, bacterial reservoirs can aid survival of the organism. In the human mouth, not only the oral mucosa but also the tongue and tonsils may serve as as reservoirs for bacteria, which, under favorable conditions, may colonize the teeth as well as the periodontal pockets. It is well known that the dorsum of the tongue is the main reservoir for Streptococcus salivarius, which is a very potent, cariogenic (acidogenic) bacteria. In one study, however, higher numbers of S mutans were repeatedly found on the dorsum of the tongue after five thorough scrapings with a tongue scraper than prior to scraping, indicating this to be an important reservoir (Axelsson et al, 1987). Lindquist et al (1989) found a significant correlation between the prevalence of S mutans in saliva and its prevalence on the dorsum of the tongue. These data support the inclusion of the dorsum of the tongue in oral hygiene procedures, at least in patients highly infected by periopathogens and/or cariogenic bacteria, such as S mutans. Although there are general definitions of habitats, studies of the oral microflora should always include careful definition of the habitats being examined. It is important to recognize that the physical dimensions of a habitat do not fall within specific limits: The whole oral cavity, an occlusal tooth surface, or even a defined area on the occlusal surface may be considered a habitat. In oral microbiology, changes in the flora of a habitat such as the saliva may indicate, for example, patients at risk of developing caries, while changes in tooth surface microenvironments can identify a surface at risk of disease.
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Comments
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Articles for theme “caries”:
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29-03-2010
Role of the Oral EnvironmentIntroductionIn certain aspects, the oral cavity may be regarded as a single microbial ecosystem. A major regulatory factor is the flow rate of saliva, which decreases to almost 0.0 mL/min during sleep, is approximately 0.4 mL/min at rest, and increases to 2.0 mL/min after stimulation. Although saliva is not a good medium for supporting the growth of many bacteria, 1.0 mL of whole saliva may contain more than 200 million microorganisms, representing more than 300 different species.
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29-03-2010
Rate of accumulation (Plaque Formation Rate Index)The quantity of plaque that forms on clean tooth surfaces during a given time represents the net result of interactions among etiologic factors, many internal and external risk indicators and risk factors, and protective factors:· The total oral bacterial population· The quality of the oral bacterial flora· The anatomy and surface morphology of the dentition· The wettability and surface tension of the tooth surfaces· The salivary secretion rate and other properties of saliva· The intake of fermentable carbohydrates· The mobility of the tongue and lips· The exposure to chewing forces and abrasion from foods· The eruption stage of the teeth· The degree of gingival inflammation and volume of gingival exudate· The individual oral hygiene habits· The use of fluorides and other preventive products, such as chemical plaque control agents This observation has been the rationale for the development of the Plaque Formation Rate Index (PFRI) by Axelsson (1989, 1991).
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29-03-2010
Measurement of plaqueAmount of accumulationSeveral indices for recording supragingival plaque have been developed. The two most frequently used are the Plaque Index (PI), developed by Silness and Loe (1964), and O’Leary’s Plaque Index (O’Leary et al, 1972).The Silness and Loe Plaque Index has a four-point scale:· Score 0 = The tooth surface is clean.· Score 1 = The tooth surface appears clean, but dental plaque can be removed from the gingival third with a sharp explorer.
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29-03-2010
According to Dawes et al (1963), dental plaque is “the soft tenacious material found on tooth surfaces which is not readily removed by rinsing with water.” It is estimated that 1 mm3 of dental plaque, weighing about 1 mg, will contain more than 200 million bacteria. Other microorganisms, such as mycoplasma, “yeasts,” and protozoa, also occur in mature plaque; sticky polysaccharides and other products form the so-called plaque matrix, which constitutes 10% to 40% by volume of the supragingival plaque.
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29-03-2010
Dental caries is an infectious, transmissible disease. As early as 1954, Orland et al demonstrated that, although germ-free animals do not develop caries, even with frequent sugar intake, all animals in the group rapidly develop carious lesions when human cariogenic bacteria (mutans streptococci) are introduced in the mouth of one animal. Specific bacteria (acidogenic and aciduric) that colonize the tooth surfaces are recognized as etiologic factors in dental caries. Frequent intake of fermentable carbohydrates, such as sugar, is regarded only as an external (environmental) modifying risk factor or prognostic risk factor.
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