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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.

• Bacteria and debris build up on tooth surfaces, and the bacteria produce acids that cause decay.
• Tooth pain occurs after decay reaches the inside of the tooth.
• Dentists can detect cavities by examining the teeth and taking x-rays periodically.
• Good oral hygiene and regular dental care plus a healthy diet can help prevent cavities.
• Fluoride treatments can help cavities in the enamel heal, but for deeper cavities, dentists must drill out the decay and fill the resulting space.

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.

Risk Factors: There are many risk factors for cavities:

• Defects in the tooth surface
• Sugary or acidic foods
• Too little fluoride in the teeth
• Reduced saliva flow

For tooth decay to develop, a tooth must be susceptible, acid-producing bacteria must be present, and nutrients must be available for the bacteria to thrive. A susceptible tooth has relatively little protective fluoride incorporated into the enamel or has pronounced pits, grooves, or 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 bacterium is Streptococcus mutans.

Spotlight on Aging Only a generation ago, most people expected to go through old age with false teeth or no teeth at all. This expectation has changed greatly during the last several decades. Although nearly half of people 85 or older have none of their natural teeth, the likelihood of losing teeth with aging is steadily decreasing. There are several reasons for this change: improved nutrition, better access to dental care, and better treatment for tooth decay and periodontal disease. When teeth are lost, chewing is greatly hindered, and speaking becomes a challenge. The face looks dramatically different without the support teeth normally provide for the lips, cheeks, nose, and chin.. People who have lost some or all of their teeth can still eat, but they tend to eat soft foods. Soft foods tend to be relatively high in carbohydrates and low in protein, vitamins, and minerals. Foods that are high in protein, vitamins, and minerals, such as meats, poultry, grains, and fresh fruits and vegetables, tend to be harder to chew. Consequently, older people who eat mainly soft foods may become undernourished. Partial or full dentures are useful for people who have lost nearly all or all of their teeth. Dentists carefully construct dentures so that they fit well and look natural. Typically, constructing dentures takes several months and involves a sequence of carefully planned steps. Once they have dentures, people should see their dentist at least once a year. The shape of the mouth can change over time or as weight is lost or gained, in which case the dentures may have to be refitted. Dentures can improve appearance and speech, but they are far from a perfect solution. They restore less than 20% of the chewing ability provided by natural teeth. Dentures can also cause discomfort and interfere with tasting. Some people find dentures embarrassing. Dentures must be kept clean. They should be removed after each meal and cleaned with toothpaste or baking soda on a toothbrush or denture brush. Also, the mouth should be cleaned to remove food debris. Dentures should be removed before going to sleep, cleaned carefully, and kept in a safe place. Soaking dentures overnight in a cleaning solution can be helpful but is not necessary if dentures are cleaned well with a toothbrush.

The nutrients that decay-causing bacteria need come from the person's diet. When infants are put to bed with a bottle, their teeth have prolonged contact with the formula or milk, 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 from drugs or disorders (such as Sjögren's 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 (almost always the mother) may pass these bacteria to a child through kissing 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.

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.

Types of Cavities The illustration on the left shows a tooth with no cavities. The illustration on the right shows a tooth with the three types of cavities.

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.

Did You Know... Parents can pass decay-causing bacteria to their children through kissing or sharing eating utensils.

Symptoms

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. People may feel pain only when drinking something cold or eating candy. This 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 Tooth Disorders: Periapical Abscess), which causes constant pain that is worse when people bite.

Diagnosis

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.

Did You Know... Over half the people in the United States have drinking water that contains enough fluoride to reduce tooth decay.

Prevention

Several general strategies are key to preventing cavities:

• Good oral hygiene and regular dental care
• Healthy diet
• Fluoride (in water, toothpaste, or both)
• Sometimes sealants and antibacterial therapy

Oral Hygiene: 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 minutes. 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 with a vertical sliding motion, it can remove plaque and food debris.

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.

Diet: 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.

People who tend to develop cavities should eat sweet snacks less often. Rinsing the mouth 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: 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—until about age 11. Water fluoridation is the most efficient way to supply children with fluoride, and over half of the United States population now has drinking water with enough fluoride to reduce tooth decay. However, 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. Dentists may apply fluoride directly to the teeth of people of any age if they are prone to tooth decay. Fluoridated toothpaste and concentrated mouth rinses containing fluoride are beneficial for adults as well as children.

Sealants: Sealants protect hard-to-reach pits and fissures (grooves), 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% after 10 years. The occasional need for repair or replacement of sealants can be assessed at periodic dental examinations.

Antibacterial Therapy: People who are very prone to tooth decay may need antibacterial therapy. Dentists first remove decayed areas and seal all pits and fissures in the teeth. Then dentists prescribe a powerful mouth rinse ( chlorhexidine Some Trade Names
HIBICLENS
) for several weeks to kill off the bacteria in any remaining plaque. The hope is that less harmful bacteria will replace the cavity-causing bacteria. To keep bacteria under control, people may use daily home fluoride rinses and chew gum containing xylitol (a sweetener that inhibits the bacteria in plaque).

A Brighter Smile Through Cosmetic Dentistry Cosmetic dentistry can dramatically improve a person's appearance. The techniques used avoid the time involved with orthodontic therapy and the loss of tooth structure necessitated by crowns and bridges. Bonding involves the attachment of tooth-colored fillings to natural teeth with minimal tooth preparation. Bonding is a conservative way to restore fractured or chipped teeth, to close spaces between the teeth, or to cover a portion of the tooth to change the shade, color, or shape. A mild acid solution is used to clean and mildly roughen the tooth surface so that a tooth-colored resin (generally made of a special type of plastic called a composite) can adhere to this surface. Bonding allows dentists to improve the appearance of the teeth without removing large amounts of tooth structure. Porcelain veneers are similar to bonding, but they use tooth-colored porcelain instead of composite to mask discoloration or change the shape of the teeth. The process requires two visits. An impression is made after the teeth are prepared. Porcelain veneers are then made in a dental prosthetic laboratory. The veneers are bonded to the teeth using a thin resin cement. Bleaching, or tooth whitening, is a process used by dentists to lighten teeth. The effectiveness of bleaching varies according to the original color of the teeth. Products used for home bleaching usually contain a peroxide gel that is placed into a custom-made closely fitting mouth-guard–like tray that holds the solution near the teeth. The bleaching agent is placed into the mouth for a few hours per day or even overnight for 2 to 4 weeks, depending on the concentration of the bleaching agent. Bleaching can also be done in a dentist's office, in which the process is much quicker. The most common side effect of bleaching is tooth sensitivity. Bleaching may not be effective for people whose teeth are darkened or discolored because of cavities, because of a side effect of some drugs or diseases, or because of a tooth that has died.

Treatment

If decay is halted before it reaches the dentin, the enamel can actually repair itself (remineralization) in conjunction with fluoride therapy. Fluoride treatment requires use of prescription-strength fluoride-containing mouthwash. 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: Fillings are made of various materials and may be put inside the tooth or around it. Silver amalgam (a combination of mercury, silver, 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. Gold Some Trade Names
See Auranofin
fillings (inlays and onlays) are excellent but are more expensive. Also, at least two dental visits are required to permanently place them.

Composite resins and porcelain fillings 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 may not last as long, particularly in the back teeth, which take the full force of chewing.

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.

Root Canal Treatment for a Badly Damaged Tooth The tooth is numbed (anesthetized). A rubber dam is placed around the tooth to isolate it from bacteria in the rest of the mouth. A hole is drilled through the chewing surface of a back tooth or the tongue side of a front tooth. Fine instruments are passed through the hole into the pulp canal space, and all the remaining pulp is removed. The canal is smoothed and tapered from the opening to the end of the root. The canal is sealed with a filling.

Bridges, Crowns, and Implants: The replacement for an extracted tooth may be a bridge—a fixed partial denture in which teeth on either side of the missing tooth are covered with crowns—or a removable partial denture. Also, implants may be used to replace missing teeth in people who have sufficient healthy bone in their jaw. Implants are metal fixtures inserted into the jawbone. The metal is a special alloy to which bone cells can attach. After a period of time, usually 4 months, the implant becomes solid with the bone, and a post is attached. Then an artificial tooth (crown) is attached to the post. The resultant tooth can handle the force of normal chewing. Implants are considered more desirable now because they do not decay, and they offer a fixed soluton to removable bridges.

Crowns, Bridges, and Implants

A crown is a cap (restoration) that fits over a tooth. Getting a properly shaped crown usually takes two visits to the dentist, although sometimes more visits are needed. On the first visit, dentists prepare the tooth by tapering it slightly, take an impression of the prepared tooth, and put a temporary crown on it. A permanent crown is then made in a dental prosthetics laboratory, using the impression. On the next visit, the temporary crown is removed, and the final crown is permanently cemented onto the prepared tooth.

Usually, crowns are made of an alloy of gold Some Trade Names
See Auranofin
or another metal. A porcelain coating can be used to mask the color of the metal. Crowns also may be made entirely of porcelain, although porcelain is harder and more abrasive than tooth enamel and may cause wear on the opposing tooth. Also, crowns made entirely with porcelain or similar material have a slightly greater tendency to break than do those made of metal.

Last full review/revision October 2008 by James T. Ubertalli, DMD