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Role of Specific Cariogenic Microflora Introduction
29-03-2010
Role of Specific Cariogenic Microflora Introduction Microorganisms implicated in the etiology of dental caries must be acidogenic as well as aciduric. To initiate carious lesions in enamel, the microorganisms must also be able to colonize the tooth surface and survive in competition with less harmful species, forming biofilms¾the so-called dental plaque. As early as 1960, Fitzgerald and Keyes showed that certain microorganisms isolated from human dental plaque, when inoculated in germ-free rodents on a high-sucrose diet, resulted in the spread of rampant caries. Therefore, dental caries should be regarded as an infectious, transmissible disease. There is abundant support for the so-called specific plaque hypothesis, introduced by Loesche (1982, 1986), which proposes that some specific species of the plaque flora be regarded as major pathogens in the etiology of dental caries. Included in the major pathogens are those bacteria associated with caries in humans and also able to induce carious lesions in experimental animals. The most important are the mutans streptococci: there are seven species, of which two, S mutans and S sobrinus, are closely associated with caries in humans. The remainder are found in animals or, if present in humans, are not highly cariogenic. The relationship of S sobrinus to caries in humans is not as well understood as that between S mutans and caries, and only recent studies identify the species separately. The second genus closely associated with caries is Lactobacillus, commonly isolated from carious dentin (Edwardsson, 1974), thought to be its main habitat in the mouth. Compared to the extensive research into identification of the mutans streptococci, much less attention has been paid to speciating lactobacilli isolated from carious lesions. Also associated with the etiology of dental caries, but considered to be less cariogenic than S mutans, S sobrinus, and Lactobacillus, are Actinomyces odontologica, Actinomyces naeslundii, and some other species of MS. To clarify the role of S mutans in the etiology of dental caries, many cross-sectional and longitudinal human studies have been conducted over the past two to three decades, particularly by the Krasse and Bratthall research groups in Sweden.
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Comments
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Articles for theme “caries”:
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29-03-2010
Strategies for prevention and control of caries based on plaque ecology hypothesis According to the plaque ecology hypothesis, low pH (less than 5) will promote overgrowth of aciduric microorganisms, such as the cariogenic mutans streptococci and lactobacilli, at the expense of less acid-tolerant plaque microorganisms, such as S oralis, which are associated with healthy tooth surfaces. Therefore the treatment strategy would be to increase plaque pH and thereby promote reestablishment of the harmless normal microflora of the tooth surfaces.
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29-03-2010
Effect of plaque ecologyOwing to differences in local environmental conditions, the microflora of mucosal surfaces differs in composition from that of dental plaque. Similarly, the plaque microflora varies in composition at distinct anatomic sites on the tooth ¾ for example, in fissures, on approximal surfaces, and in the gingival crevice. The resident microflora of a site acts as part of the host defenses by preventing colonization by exogenous (and often pathogenic) microorganisms.
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29-03-2010
Colonization of microenvironmentsThe 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.
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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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