Caries is caused by acids produced by bacteria in dental plaque. Plaque is, at first, a soft, thin film of bacteria, mucin, dead epithelial cells, and food debris that develops on the tooth surface within about 24 hours after the tooth is cleaned. Streptococcus mutans species are a group of related bacteria that grow in plaque and can cause caries. Some strains are more cariogenic than others. Eventually (commonly, after 72 hours), soft plaque mineralizes, mainly with calcium, phosphate, and other minerals, becoming calculus (hard plaque or tartar), which cannot easily be removed with a toothbrush.
There are several risk factors for caries:
Inadequate plaque control
Frequent dietary carbohydrates and sugars
High-acid and/or low-fluoride environment
Reduced salivary flow (eg, due to drugs, radiation therapy, systemic disorders that cause salivary gland dysfunction)
Many teeth have open enamel pits, fissures, and grooves, which may extend from the surface to the dentin (see figure Types of cavities). These defects may be wide enough to harbor bacteria but too narrow to clean effectively. They predispose teeth to caries.
Frequent dietary exposure to carbohydrates and sugars promotes the growth of plaque-forming bacteria. Development of severe early childhood caries (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). Thus, bedtime bottles should contain only water.
A tooth surface is more susceptible to caries when it is poorly calcified, has low fluoride exposure, and/or is in an acidic environment. Typically, decalcification begins when the pH at the tooth falls below 5.5 (eg, when lactic acid–producing bacteria colonize the area or when people drink soft drinks, sports drinks or energy drinks, which commonly have pH values below 5.5).
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, exposure of root surfaces, and declining manual dexterity (causing ineffective oral hygiene).
Caries initially involves only the enamel and causes no symptoms. Caries 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 (pulpitis).
Routine, frequent clinical evaluation (every 3 to 12 months depending on a patient's caries risk as assessed by a dentist) 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, although infrequently these are supplemented by new devices that detect caries by changes in electrical conductivity or laser reflectivity. However, x-rays are still most important for detecting caries, determining the depth of involvement, and identifying caries under existing restorations.
The primary treatment of caries that has entered dentin is removal by drilling, followed by filling of the resultant defect.
Fillings for occlusal surfaces of posterior teeth, which bear the brunt of mastication, must be composed of strong materials, including
Silver amalgam combines silver, mercury, copper, tin, and occasionally zinc, palladium, or indium. Amalgam is inexpensive and lasts an average of 14 years. However, if oral hygiene is good and if amalgam was placed using a rubber dam for isolation from saliva, many amalgam fillings last > 40 years. Amalgam is a highly durable material with annual failure rates lower than that of composite resins. Amalgam use is decreasing mainly due to its appearance compared to that of composites and environmental concerns related to the removal and disposal of its mercury content. 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 not recommended because it is expensive, damages tooth structure, actually increases patient exposure to mercury, and requires the use of amalgam separators to eliminate disposal of its mercury content into the environment.
Composite resins, which have a more acceptable appearance, have long been used in anterior teeth, where aesthetics are primary and the forces of chewing are minimal. Many patients request them in posterior teeth as well, and they are now commonly used there. Early-generation composite resins under high occlusal stress generally lasted less than half as long as amalgam and tended to develop recurrent decay because the composite resin shrinks when it hardens and expands and contracts with heat and cold more than the tooth or other filling materials. The current generation of composites also closely simulates enamel hardness but does not appear to have the same incidence of recurrent caries as earlier materials, and may also last longer. Use of bonded composite resin restorations allows for more conservation of tooth structure compared to amalgam preparations.
Glass ionomer, a tooth-colored filling, releases fluoride when in place, a benefit for patients especially prone to tooth decay. It is also used to restore areas damaged by overzealous brushing. Glass ionomer is not as aesthetic as composite and it should not be used on chewing surfaces because it has a high wear rate. Resin-modified glass ionomer materials are also available and provide some improved aesthetics compared to conventional glass ionomers.
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 procedure necessitates a root canal filling, in which an opening is made in the tooth and the pulp is removed. The root canal system is thoroughly debrided, shaped, and then filled with gutta-percha. The outer tooth surfaces (what would have been the enamel) are then reduced so that an artificial crown, usually made of metal, porcelain, or ceramic can be placed. Crowns for anterior teeth are made of, or covered with, porcelain or ceramic.
For most people, caries is preventable. Cavities first form on permanent teeth in the early teens to late 20s. Caries-prone people typically have low exposure to fluoride and a relatively cariogenic microflora acquired from their mothers and through social contact. Maintaining good oral hygiene and minimizing sugar intake are especially important.
Removal of plaque at least every 24 hours, 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. Brushing with an electric toothbrush for 2 minutes is excellent; brushing with a manual soft toothbrush for 3 to 4 minutes 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 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, oral fluoride supplements are recommended for children from 6 months through 16 years; fluoride supplements in pregnant women have not been shown to prevent caries in offspring and thus are no longer recommended (1). The dose must be selected according to the amount of fluoride present in the drinking water and diet, the age of the child, and whether topical fluoride is being used in toothpaste and/or applied during dental care. The total dose should not be so high as to cause dental fluorosis. Fluoridated toothpaste should also be used by people of all ages. Because young children may swallow toothpaste when brushing, which can lead to fluorosis, they should use children's toothpastes, which contain lower amounts of fluoride.
Fluoridation offers less protection against caries in pits and fissures than against those on smooth surfaces. Deep, narrow pits and fissures require use of sealants (resin materials that adhere tightly to the surface of the enamel) to prevent nutrients from reaching bacteria, reducing their growth and acid production.
If these measures do not decrease cavity formation, more intensive therapy is aimed at changing the flora. After cavities are treated, pits and fissures, which can harbor S. mutans, are sealed. This treatment is followed by a 0.12% chlorhexidine mouth rinse used for 60 seconds twice a day for 2 weeks, which may reduce the cariogenic bacteria in plaque and allow repopulation with less cariogenic strains of S. mutans. To encourage this repopulation, xylitol in the form of hard candy or chewing gum is used for 5 minutes three times a day. Additionally, a 5000 ppm high-fluoride toothpaste regimen may be prescribed, or 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, preventive measures focusing on improved oral health are recommended (eg, limiting sugary food and drinks, brushing twice daily with toothpaste containing fluoride, daily flossing, and occasionally alcohol-free mouth rinses containing chlorhexidine). If this is not feasible, the mother can use xylitol, as mentioned above, from the time of the child’s birth to the age at which the mother no longer samples the child’s food (a hypothesized mode of transfer). Prenatal interventions may reduce transfer of cariogenic bacteria from mother to child and delay caries formation in the child.
For prevention of caries in deciduous teeth (once they have erupted) in infants, bedtime bottles should contain only water.
Caries is caused by acids produced by bacteria in dental plaque.
Risk factors include preexisting tooth defects, low saliva flow, an acidic oral environment, frequent exposure to carbohydrates and sugar in the diet, and inadequate exposure to fluoride.
Treatment involves drilling out the decayed area and restoring the defect with amalgam or a composite resin.
Prevention involves meticulous regular brushing, flossing, and professional cleaning; adequate fluoride must be available in toothpaste and, when not present in drinking water, as oral supplements for children.