Tooth Decay (Caries)

Caries is the most common dental disease. If the individual it affects is suitably predisposed, caries destroys the dental hard tissue by a chemicoparasitic process. Caries starts on the surface of the tooth, usually in the enamel of the dental crown (initial caries) or on the exposed cementum at the neck of the tooth (caries of cementum), and it goes on to attack the dentin.

The caries lesion initially takes the form of an opaque, chalky spot in the enamel; as demineralization progresses, the tooth surface becomes rougher. After destruction of the enamel layer, brown-colored cavities develop in the dentin. At this stage, cold, heat, or sweet foods will trigger a transitory throbbing pain. Progressive caries is first accompanied by infection, inflammation, and destruction of the pulp. Then the periodontal tissue is attacked, leading to loss of the affected tooth as a result of inflammatory processes. Several factors encourage the formation of caries:

Susceptibility of tissue to disease (tooth)
Bacterial coating on the teeth (plaque)
Consumption of cariogenic substrates (carbohydrates)
Flow and composition of saliva
Shape and position of teeth

The chemical composition of dental hard substances has an influence on the development of caries.The high fluoride content of enamel has an anticaries effect, whereas a high carbonate content in enamel encourages caries.

Plaque is a tough, matted, sticky coating on teeth made up of bacterial cells (streptococci are particularly cariogenic) and an intercellular matrix. Plaque forms on unclean areas of the tooth (preferred sites for caries), particularly in pits and fissures, the approximal surfaces, and in the cervical area (Fig 9-9). These sites are first colonized by aerobic microorganisms (which live in oxygen) and later by anaerobes (which do not require oxygen). Once plaque is fully developed, it can no longer be removed by self-cleaning mechanisms of the masticatory system. Plaque is mineralized into tartar (calculus) by constituents of saliva. Tartar forms close to the excretory ducts of the large salivary glands, ie, on the lingual surfaces of the anterior mandibular teeth and the buccal surfaces of the maxillary first molars.

The fermentation of carbohydrate food remnants (low-molecular weight carbohydrates, monosaccharides) in plaque on the teeth acidifies the oral environment. This gives rise to lactic acid, which demineralizes the dental hard tissue while releasing salts (calcium and phosphate salts) (Fig 9-10). The tooth surface becomes rough and provides greater retention for food particles with increased fermentation. Bacteria are able to migrate into the loosened, demineralized tooth surface, where they then break down the organic supportive framework of the tooth (Figs 9-11 to 9-13).

Diet can encourage the formation and progression of caries lesions. Low-molecular weight carbohydrates such as sugar, glucose, and maltose allow caries to develop. By contrast, fatty foods (eg, cheese) have an anticaries effect because fat envelops the tooth material with a film. Saliva has a caries-preventive effect because of its rinsing function (quantity, viscosity) and its composition (sialic acid, pH).

Treatment of caries involves removing the diseased dental tissue, then restoring the original tooth shape by means of a dental filling, taking account of functional and cosmetic aspects. The following measures can be taken to prevent caries:

Consuming a mixed diet rich in vitamins and mineral salts during the period of tooth development
Eating foods that require chewing, which causes smoothing of the masticatory surface through abrasion and leads to self-cleaning because more saliva is secreted
Early orthodontic measures for positional anomalies
In certain circumstances, fluoride prophylaxis by the intake of suitable fluoride compounds (eg, drinking water containing low concentrations of fluoride)
Coating the tooth surface with fluoride solutions, which means that poorly soluble hydroxy-fluorapatite forms in the tooth enamel
Careful dental hygiene
Regular 6-month dental checkups
Early filling even of small lesions

Erosion denotes the chemical dissolution of dental enamel without the involvement of microorganisms. It mainly happens on smooth tooth surfaces and is usually caused by acid vapors or consumption of acidic fruit juices or fizzy drinks.

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