Text I. Caries-producing microorganisms

Healthy tooth	Early decay	Advanced decay

Caries is a disintegration of the teeth beginning at surface and progressing inward. First the surface enamel, which is entirely noncellular, is demineralised. This has been attributed to the effect of acid products of bacterial fermentation.

Subsequent decomposition of the dentin and cement involves bacterial digestion of the protein matrix. An essential first step in caries production appears to be the formation of plaque on the hard, smooth enamel surface. The plaque consists mainly of gelati?nous deposits of high-molecular-weight glucans in which acid-producing bacteria adhere to the enamel. The carbohydrate polymers (glucans) are produced mainly by streptococci (Streptococcus mutans, peptostreptococci), perhaps in association with actinomycetes. There is a strong correlation be?tween the presence of S mutans and caries on specific enamel areas. The essential second step in caries pro?duction is the formation of large amounts of acid (pH < 5.0) from carbohydrates by streptococci and lactobacilli in the plaque. High concentrations of acid demineralize the adjoining enamel and initiate caries.

In experimental "germ-free" animals, cariogenic streptococci can induce the formation of plaque and caries. Adherence to smooth surfaces requires both the synthesis of water-insoluble glucan polymers by glucosyltransferases and the participation of binding sites on the surface of microbial cells. (Perhaps carbohy?drate polymers also aid the attachment of some strep?tococci to endocardial surfaces.)

Certain diphtheroids and streptococci can induce specific soft tissue damage and bone resorption typical of periodontal disease. Proteolytic organisms, including actinomycetes and bacilli, play a role in the microbial action on dentin that follows damage to the enamel. Periodontal pockets in the gingiva are particularly rich sources of organisms, including anaerobes. The development of caries also de?pends on genetic, hormonal, nutritional, and many other factors. Control of caries involves physical re?moval of plaque, limitation of sucrose intake, good nu?trition with adequate protein intake, and reduction of acid production in the mouth by limitation of available carbohydrates and frequent cleansing. The application of fluoride to teeth or its ingestion in water results in enhancement of acid resistance of the enamel.

Identification of the source of infection with the bacteria respon?sible for caries provides us with a potential way of developing a preventive strategy. It may not be feasible to achieve a lifetime free of S. mutans, but delaying the age at which a child becomes infected can reduce their subsequent caries risk.

Macrowiar P.A. The normal microbial flora. NEJM

Date: 2016-06-12; view: 5