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Caries is
tooth decay, commonly called cavities. The symptoms—tender, painful
teeth—appear late. Diagnosis is based on inspection, probing of
the enamel surface with a fine metal instrument, and dental x-rays.
Treatment involves removing affected tooth structure and restoring it
with various materials. Fluoride, diligent dental hygiene, sealants,
and proper diet can prevent virtually all caries.
Etiology
and Pathophysiology
Caries is caused by acids produced by bacteria retained within dental plaque. Plaque is, at first, a soft, thin film of food debris, mucin, dead epithelial cells, and bacteria that develops on the tooth surface within about 24 h after the tooth is cleaned. Mutans
streptococci is a group of related bacteria causing caries. Some strains are more cariogenic than others. Eventually, the soft plaque becomes hard with Ca and other minerals (hard plaque), which cannot easily be removed with a toothbrush.
Many teeth have open enamel pits, fissures, and grooves, which may extend from the surface to the dentin. These defects may be wide enough to harbor bacteria but too narrow to clean effectively. They predispose teeth to caries.
A tooth surface is more susceptible to caries when it is poorly calcified or in an acidic environment. Typically, decalcification begins when the pH at the tooth falls below 5.5 (as occurs with colonization by acid-producing bacteria and/or with the drinking of cola beverages, which contain phosphoric acid).
Rampant caries in deciduous teeth suggests prolonged contact with infant formula, milk, or juice, typically when an infant goes to bed with a bottle (baby or nursing bottle caries).
The elderly often take drugs that reduce salivary flow, predisposing to caries. The elderly also have a higher incidence of root caries because of gingival recession and exposure of root surfaces.
Untreated caries leads to tooth destruction, infections, and the need for extractions and replacement prostheses. Premature loss of deciduous teeth may shift the adjacent teeth, hindering eruption of their permanent successors.
Symptoms,
Signs, and Diagnosis
Caries initially involves only the enamel and produces no symptoms. A cavity that invades the dentin causes pain, first when hot, cold, or sweet foods or beverages contact the involved tooth, and later with chewing or percussion. Pain can be intense and persistent when the pulp is severely involved (see Common Dental Disorders: Pulpitis).
Routine, frequent (q 6 to 12 mo) clinical evaluation identifies early caries at a time when minimal intervention prevents its progression. A thin probe, sometimes special dyes, and transillumination by fiberoptic lights are used, frequently supplemented by new devices that detect caries by changes in electrical conductivity, as well as laser reflectivity. However, x-rays are still important for detecting caries, determining the depth of involvement, and identifying caries under existing restorations.
Treatment
Incipient caries should be remineralized, if possible, through cleanings and multiple fluoride applications.
The primary treatment of caries is removal by drilling, followed by filling of the resultant defect. For very deep cavities, a temporary filling may be left in place 6 to 10 wk in the hope that a tooth will deposit reparative dentin, preventing exposure of the pulp, which necessitates root canal treatment. Fillings for occlusal surfaces of posterior teeth, which bear the brunt of mastication, must be composed of strong materials. The most common material has been silver amalgam, a combination of silver, mercury, copper, tin, and, occasionally, zinc, palladium, or indium. Amalgam is inexpensive and lasts an average of 14 yr. However, with good oral hygiene and if placed with use of a rubber dam for isolation from saliva, many amalgam fillings last > 40 yr. Although concern has been raised about mercury poisoning, the number of amalgam fillings a person has bears no relationship to blood mercury levels. Replacing amalgam is expensive, damages tooth structure, and is not recommended.
Composite resins, which have a more acceptable appearance, have long been used in anterior teeth, where aesthetics is primary and the forces of chewing are minimal. Some patients request them in posterior teeth as well. However, composite resins under high occlusal stress generally last less than half as long as amalgam and tend to develop recurrent decay. This occurs because the material shrinks when it hardens and also expands and contracts with heat and cold more than tooth or other filling materials. Newer porcelain or ceramic inlays resemble enamel, but long-term results are not yet known.
If decay leaves too little dentin to hold a restoration, a dentist replaces the missing dentin with cement, amalgam, composite, or other materials. Sometimes a post must be inserted into one or more roots to support a gold, silver, or composite core, which replaces the coronal dentin. This may necessitate a root canal filling. The outer tooth surfaces (what would have been the enamel) are then reduced so that an artificial crown, usually made of gold, porcelain, or both, can be placed. Crowns for anterior teeth consist of, or are covered with, porcelain.
Prevention
For most people, caries is preventable. Removal of plaque at least q 24 h, usually by brushing and flossing, helps prevent dental caries. The gingival third of the tooth is the most important area to clean but is the area most often neglected. Electric and electronic toothbrushes are excellent, but a manual soft toothbrush, used for an average of 3 to 4 min, suffices. Using excess toothpaste, particularly an abrasive type, may erode the teeth. Dental floss is placed between each of the teeth, curved against the side of each tooth, and moved up and down 3 times, going just beneath the gingival margin. Flosses that are very thin (dental tape) or coated with wax or polytetraethylene can be used for exceptionally tight contacts between teeth or rough filling margins.
Teeth with fluoride incorporated into their enamel are more resistant to acidic decalcification and more readily recalcify when pH increases. If drinking water is not adequately fluoridated, fluoride supplements are recommended for children from shortly after birth through age 8 yr and for pregnant women beginning at 3 mo gestation (when teeth are forming in the fetus). The dose must be selected according to the amount of fluoride present in the drinking water and the age of the child. The total dose should not be so high as to cause dental fluorosis. Fluoridated toothpaste should also be used by people of all ages.
Fluoridation offers less protection against caries in pits and fissures compared with those on smooth surfaces. Pits and fissures require use of sealants (plastic materials that adhere tightly to the surface of the enamel) to prevent nutrients from reaching bacteria, reducing their growth and acid production.
Cavities first form on permanent teeth in the early teens to late 20s. A caries-prone subset typically has a low fluoride exposure and a relatively cariogenic microflora acquired from the mother. Maintaining good oral hygiene and minimizing sugar intake are especially needed.
If these measures do not decrease cavity formation, more intensive therapy aims at changing the flora. After cavities are treated, pits and fissures, which can harbor M. streptococci are sealed. This treatment is followed by 60-sec mouth rinses using 0.12% chlorhexidine bid for 2 wk, which may reduce the cariogenic bacteria in plaque and allow repopulation with less cariogenic strains of M. streptococci. To encourage repopulation, xylitol in the form of hard candy or chewing gum is used for 5 min tid. Additionally, topical fluoride may be applied by a dentist or used at night in a custom-made fluoride carrier.
For pregnant women with a history of severe caries, the above regimen may be used before the child's teeth erupt. If this is not feasible, the mother can use xylitol, as mentioned above, from the time of the baby's birth to the age at which the mother no longer samples the child's food (the hypothesized mode of transfer).
For prevention of caries in deciduous teeth (once they have erupted) in infants, bedtime bottles should contain only water.
Last full review/revision November 2005
Content last modified November 2005
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