Dental decay (caries)

A disease in which the mineralized tissues of the tooth undergo progressive destruction from the surface of the tooth. It is caused by bacteria that colonize the tooth surface and, under certain conditions, produce sufficient acids to demineralize the enamel covering of the tooth crown or the cementum covering the root, and then the underlying dentin. As the destruction of the dentin progresses, along with breakdown of the organic components, the bacteria invade the dead tissue and enter the pulp chamber.
The pulpal tissue becomes infected and the typical toothache may ensue. The infection can ultimately destroy the pulpal tissue and extend through the apical openings of the roots and into the surrounding peri-odontal tissues.
The sites of caries development have been correlated with the presence of dental plaque containing one of a number of mutans streptococci-notably in humans. Streptococcus mutans and S. sobrinus. These microorganisms are cariogenic because of their ability to generate a considerable amount of acid as a result of their metabolism of carbohydrates, and to survive in an acid environment.

The acid environment is only slowly neutralized since its dilution is hindered by the fact that the acid is within the dental plaque and thereby shielded from the saliva. Each time a carbohydrate-rich substance is ingested, acid is formed. Therefore, the frequency of ingestion and physical consistency of fermentable carbohydrates are important factors in caries formation.
Dental caries can be prevented by making the tooth less susceptible to acid attack, removing cariogenic bacteria from the teeth, and limiting ingestion of cariogenic substrate.
The most effective and least expensive means of rendering the tooth less susceptible to the caries attack is through fluoridation, either by systemic means such as water fluoridation, or by topical application of fluoride to the tooth surfaces. Water fluoridation (approximately 1 part per million) by itself reduces the incidence of caries by 50-60%. Topical fluoridation can be instituted by many means, ranging from professional applications in the dental office to self-applied fluoride in the form of toothpastes, mouth rinses, and gels. The mode of action of fluoridation is not fully understood, but the benefit to the tooth structure is probably a result of a number of actions. It is believed that fluoride, when incorporated into the mineral phase of enamel and the other hard tissues, results in a better crystalline structure that is less susceptible to acid dissolution. Alternatively, the anticaries effect of fluoride may be due to its ability to inhibit demineralization and promote remineralization. Other means of improving the tooth's resistance to dental caries include the application of plastic pit and fissure sealants which eliminate retentive areas on the biting surfaces of the posterior teeth that are more susceptible to carious lesions.

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