Cavities (dental caries) are decayed areas in the teeth, the result of a process that gradually dissolves a tooth's hard outer surface (enamel) and progresses toward the interior.
Along with the common cold and gum disease, cavities are among the most common human afflictions. If cavities are not properly treated by a dentist, they continue to enlarge. Ultimately, an untreated cavity can lead to tooth loss.
There are many risk factors for cavities:
For tooth decay to develop, a tooth must be susceptible, acid-producing bacteria must be present, and nutrients (such as sugar) must be available for the bacteria to thrive and produce acid. A susceptible tooth has relatively little protective fluoride incorporated into the enamel or has pronounced pits, grooves, or cracks (fissures) that retain plaque. Poor oral hygiene that allows plaque and tartar to accumulate can accelerate this process. Although the mouth contains large numbers of bacteria, only certain types generate acid, which causes decay. The most common decay-causing bacteria are Streptococcus mutans.
The nutrients that decay-causing bacteria need come from the person's diet. When infants are put to bed with a bottle that contains anything but plain water, their teeth have prolonged contact with the formula, milk, or juice, which increases the likelihood of decay. Large amounts of sugar in the diet also provide food for the bacteria.
Acid in the diet (for example, in cola beverages, which contain phosphoric acid) accelerates tooth decay.
Reduced saliva flow due to drugs or disorders (such as Sjögren syndrome) places people at greater risk of tooth decay. Older people often take drugs that reduce saliva flow, increasing their risk of cavities.
Some people have especially active decay-causing bacteria in their mouth. A parent may pass these bacteria to a child through kissing, sampling the child's food, or sharing eating utensils. The bacteria flourish in the child's mouth after the first teeth come in and can then cause cavities. So, a tendency toward tooth decay that runs in families does not necessarily reflect poor oral hygiene or bad eating habits. These bacteria can also be spread through social contact with people outside the family.
Gum recession also makes cavities more likely to develop because it can expose the roots of teeth. Then bacteria can access the inner layers of the tooth more easily. Gum recession makes older people prone to root cavities.
Progression of tooth decay:
Decay in the enamel progresses slowly. After penetrating into the second layer of the tooth—the somewhat softer, less resistant dentin—decay spreads more rapidly and moves toward the pulp, the innermost part of the tooth, which contains the nerves and blood supply. Although a cavity may take 2 or 3 years to penetrate the enamel, it can travel from the dentin to the pulp—a much greater distance—in as little as a year. Thus, root decay that starts in the dentin can destroy a lot of tooth structure in a short time.
Smooth surface decay, the most preventable and reversible type, grows the slowest. In smooth surface decay, a cavity begins as a white spot where bacteria dissolve the calcium of the enamel. Smooth surface decay between the permanent teeth usually begins between the ages of 20 and 30.
Pit and fissure decay, which usually starts during the teen years in the permanent teeth, forms in the narrow grooves on the chewing surface and on the cheek side of the back teeth. Decay at these locations progresses rapidly. Many people cannot adequately clean these cavity-prone areas because the grooves are narrower than the bristles of a toothbrush.
Root decay begins on the root surface covering (cementum) that has been exposed by receding gums, usually in people past middle age. This type of decay often results from difficulty cleaning the root areas, a lack of adequate saliva flow, a diet high in sugar, or a combination of these factors. Root decay can be the most difficult type of tooth decay to prevent and treat.
Whether tooth decay causes pain depends on which part of the tooth is affected and how deeply the decay extends. A cavity in the enamel causes no pain. The pain starts when the decay reaches the dentin. At first, people may feel pain only when hot, cold, or sweet foods or beverages come in contact with the affected tooth. This pain indicates that the pulp is still healthy. If the cavity is treated at this stage, dentists can restore the tooth, and most likely no further pain or chewing difficulties will develop.
A cavity that gets close to or actually reaches the pulp causes irreversible damage. Pain lingers even after a stimulus (such as cold water) is removed. The tooth may hurt even without stimulation (spontaneous toothache).
If irreversible damage to the pulp occurs and the pulp subsequently dies, the pain may stop temporarily. The tooth then may become sensitive when people bite or when the tongue or a finger presses on it because the area at the end of the root has become inflamed or because infection has developed at the root. Infection may produce a collection of pus (abscess—see see Periapical Abscess), which causes constant pain that is worse when people bite.
If a cavity is treated before it starts to hurt, the chance of damage to the pulp is reduced, and more of the tooth structure is saved. To detect cavities early, a dentist inquires about pain, examines the teeth, probes the teeth with dental instruments, and may take x-rays. People should have a dental examination every 6 to 12 months. Not every examination includes x-rays. Depending on the dentist's assessment of a person's teeth, x-rays may be taken every 12 to 36 months.
Several general strategies are key to preventing cavities:
Good oral hygiene, which involves brushing before or after breakfast and before bedtime and flossing daily to remove plaque, can effectively control smooth surface decay. Brushing helps prevent cavities from forming on the top and sides of the teeth, and flossing gets between the teeth where a brush cannot reach.
Electric and ultrasonic toothbrushes are excellent, but an ordinary toothbrush, used properly, is quite sufficient. Normally, proper brushing takes only about 3 to 4 minutes. People should avoid using too much toothpaste, especially abrasive types, which may erode the teeth. Floss is gently moved back and forth between the teeth, then wrapped around the tooth and root surfaces in a “C” shape at the gum line. When the floss is moved up and down 3 times, it can remove plaque and food debris. There are many small, toothpick-like devices (called interproximal brushes) with bristles or plastic projections on the ends that can be used to clean between teeth. These devices are more effective than flossing but only if there is enough space between the teeth to accommodate them. They come in many sizes and shapes and can be used alone or with different toothpastes or rinses.
Initially, plaque is quite soft, and removing it with a soft-bristled toothbrush and dental floss at least once every 24 hours makes decay unlikely. Once plaque begins to harden, a process that begins after about 72 hours, removing it becomes more difficult.
Although all carbohydrates can cause tooth decay to some degree, the biggest culprits are sugars. All simple sugars, including table sugar (sucrose) and the sugars in honey (levulose and dextrose), fruit (fructose), and milk (lactose), have the same effect on the teeth. Whenever sugar comes in contact with plaque, Streptococcus mutans bacteria in the plaque produce acid. The amount of sugar eaten is of little consequence. The amount of time the sugar stays in contact with the teeth is what matters. Thus, sipping a sugary soft drink over an hour is more damaging than eating a candy bar in 5 minutes, even though the candy bar may contain more sugar. Infants who go to bed with a bottle, even if it contains only milk or formula, are also at risk of cavities. Bedtime bottles should contain only water.
People who tend to develop cavities should eat sweet snacks less often. Rinsing the mouth with water after eating a snack removes some of the sugar, but brushing the teeth is more effective. Drinking artificially sweetened soft drinks also helps, although diet colas contain acid that can promote tooth decay. Drinking tea or coffee without sugar also can help people avoid cavities, particularly on exposed root surfaces.
Fluoride can make the teeth, particularly the enamel, more resistant to the acid that helps cause cavities. Fluoride taken internally is effective while the teeth are growing and hardening. Water fluoridation is the most efficient way to supply children with fluoride, and over half of the population of the United States now has drinking water that contains fluoride. However, many people may not consume enough of this water to significantly reduce tooth decay. Conversely, if a water supply has too much fluoride, the teeth can become spotted or discolored (fluorosis). If a child's water supply does not have enough fluoride, doctors or dentists can prescribe sodium fluoride drops or tablets. Children begin taking the drops or tablets shortly after birth through age 8. Pregnant women can begin taking tablets when they are 3 months pregnant (when teeth are forming in the fetus). For people of any age, dentists may apply fluoride directly to the teeth or have people wear at night a custom-made mouth guard that holds fluoride if they are prone to tooth decay. Fluoridated toothpaste is beneficial for adults as well as children.
Sealants protect hard-to-reach pits and fissures, particularly on the back teeth. After thoroughly cleaning the area to be sealed, dentists roughen the enamel with an acid solution to help the sealant adhere to the teeth. Dentists then place a liquid plastic in and over the pits and fissures of the teeth. When the liquid hardens, it forms such an effective barrier that any bacteria inside a pit or fissure stop producing acid because food can no longer reach them. About 90% of the sealant remains after 1 year and 60% remains after 10 years. The occasional need for repair or replacement of sealants can be assessed at periodic dental examinations.
People who are very prone to tooth decay may need antibacterial therapy. Dentists first remove cavities and seal all pits and fissures in the teeth. Then dentists prescribe a powerful mouth rinse (chlorhexidine) that is used for 2 weeks to kill off the bacteria in any remaining plaque. A long-acting form of chlorhexidine can also be applied by a dentist. The hope is that less harmful bacteria will replace the cavity-causing bacteria. To keep bacteria under control, people may chew gum or hard candy containing xylitol (a sweetener that inhibits the bacteria in plaque).
Antibacterial therapy can be used by pregnant women who have a history of severe cavities. Pregnant women who cannot tolerate antibacterial therapy can use xylitol as mentioned above. Xylitol is used from the time the child is born until the age at which the mother no longer samples the child's food. Xylitol helps prevent the mother's bacteria from being passed to the child.
If decay is halted before it reaches the dentin, the enamel can actually repair itself (remineralization) if people use fluoride. Fluoride treatment requires use of prescription-strength high-fluoride toothpastes and many applications of fluoride at the dentist's office. Once decay reaches the dentin, dentists drill out the decayed material inside the tooth and then fill the resulting space with a filling (restoration). Treating the decay at an early stage helps maintain the strength of the tooth and limits the chance of damage to the pulp.
Fillings are made of various materials and may be put inside the tooth or around it. Silver amalgam (a combination of silver, mercury, copper, tin, and, occasionally, zinc, palladium, or indium) is most commonly used for fillings in back teeth, where strength is important and the silver color is relatively inconspicuous. Silver amalgam is relatively inexpensive and lasts an average of 14 years. However, the amalgam can last for more than 40 years if it is carefully placed using a rubber dam and the person's oral hygiene is good. The minute amount of mercury that escapes from silver amalgam is too small to affect health. Dentists do not recommend replacing amalgam because the procedure is expensive, damages tooth structure, and actually increases a person's exposure to mercury.
Gold fillings (inlays and onlays) are excellent but are more expensive. Also, at least two dental visits are required to permanently place them.
Composite resins are used in the front teeth, where silver would be conspicuous. Increasingly, these fillings are also being used in back teeth. Although they have the advantage of being the color of the teeth, they are more expensive than silver amalgam and are more likely to develop 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. Composite resins also may not last as long as silver amalgam, particularly in the back teeth, which take the full force of chewing. Newer composite resins may develop fewer cavities and last longer but they have not been used long enough for dentists to be sure of the long-term results.
Glass ionomer, a tooth-colored filling, is formulated to release fluoride once in place, a benefit for people especially prone to tooth decay. Glass ionomer is also used to restore areas damaged by overzealous brushing.
Root canal treatment and tooth extraction:
When tooth decay advances far enough to permanently harm the pulp, the only way to eliminate pain is to remove the pulp by root canal (endodontic) treatment or tooth removal (extraction).
If a tooth is extracted, it should be evaluated for replacement as soon as possible. Otherwise, neighboring teeth may change position and alter the person's bite. There are many options for replacement of extracted teeth (see Dental Appliances).
Last full review/revision August 2013 by James T. Ubertalli, DMD