Cavities are areas of tooth decay caused by bacteria.


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Grin, Don't Bear It

Michael's friend Ashley always said that she loved his smile, and Michael wanted to keep it that way. However, Michael was unaware that he had a small cavity starting in one of his front teeth. Even though Michael had felt a little twinge now and then when he ate ice cream and candy, his favorite foods, he had not paid much attention. Michael never would have known that he had a cavity if he had not gone to the dentist for a regular checkup. Luckily, the dentist was able to drill out the decay and fill the cavity before it got worse. Michael vowed to do a better job in the future of brushing, flossing, and cutting back on sugary snacks.

What Are Cavities?

Cavities, also known as caries (KARE-eez), are areas of decay on the teeth that are caused by bacteria * . They are one of the most common of all human diseases. Almost half of American children have had a cavity by age four. Not only children have cavities, however. Teenagers and adults also are prone to tooth decay. Fortunately, most cavities can be prevented by taking good care of the teeth, eating a healthy diet, and getting regular dental care.

What Causes Cavities?

The human mouth is home to a host of bacteria. The type of bacteria that causes cavities most often is Streptococcus mutans (strepto-KOK-us MU-tanz), but other types play a role, too. Such bacteria in the mouth change the sugars and starches in food to acid. The bacteria and acid combine with mucus * and food particles, forming a sticky mass called plaque on the teeth. Plaque is the rough substance that people feel when running their tongue over their teeth several hours after brushing.

* bacteria (bak-TEER-ee-a) are round, spiral, or rod-shaped single-celled microorganisms without a distinct nucleus that commonly multiply by cell division. Some types may cause disease in humans, animals or plants.

* mucus (MYOO-kus) is a kind of body slime. It is thick and slippery, and it lines the inside of many parts of the body.

The acid in plaque can eat a hole in a tooth's enamel, the hard substance that covers and protects the outside surfaces of the tooth. People hardly notice the cavity at this stage, or they might feel a slight twinge when eating foods that are sweet, very cold, or very hot. However, bacteria that enter the hole in the enamel can make their way through the softer inside parts of the tooth. Eventually, the bacteria may reach the tooth's pulp, the soft tissue in the center of the tooth that contains nerves and blood vessels. When this happens, the blood vessels can swell and press on the nerves, causing a painful toothache. Left untreated, infection of the pulp by bacteria can cause the blood vessels and nerves in the tooth to die.

Plaque sticks best in the pits and grooves of the back teeth, just above the gums, between the teeth, and around the edges of earlier fillings. Cavities are most likely to form in these areas.

Cavities are most likely to form in the areas where plaque sticks to the teeth. The acid in plaque can eat a hole in a tooth's enamel, allowing bacteria to reach the tooth's pulp. Left untreated, infection of the pulp can cause the blood vessels and nerves in the tooth to die.
Cavities are most likely to form in the areas where plaque sticks to the teeth. The acid in plaque can eat a hole in a tooth's enamel, allowing bacteria to reach the tooth's pulp. Left untreated, infection of the pulp can cause the blood vessels and nerves in the tooth to die.

Who Gets Cavities?

Anyone can get cavities. They are most common in children, young adults, and the elderly. People who eat a diet filled with sugary foods also have a high risk of developing cavities, since the more sugar people eat, the more cavity-causing acid they make. People who already have a lot of fillings have an increased risk as well, since the area around fillings is an ideal spot for decay to start.

How Are Cavities Treated?

Cavities are usually painless during the early stages. Most are found during regular dental checkups. A dental x-ray can find cavities that are hard to see. Treating cavities early can prevent later pain and tooth loss.

If a cavity is found, the decay process can be stopped by removing the decayed part of the tooth with a special drill. If there is a lot of decay, or if a tooth is very sensitive, the dentist may give the person a shot of anesthetic * or have the person breathe an anesthetic gas before drilling. The decayed material is then replaced with a filling. Such fillings can be made from a number of materials. The most common is silver amalgam (a-MAL-gam), an alloy of silver and other metals, which is used mainly in back teeth. Fillings in the front usually are made of other materials that match the color of the teeth.

Sometimes, there is so much decay that removing it all leaves a tooth weak and easily broken. In that case, the dentist may fit the person with a crown, an artificial replacement for the part of the tooth above the gum. The crown is made in a laboratory, and then it is cemented to what is left of the tooth.

If the tooth is very seriously decayed or infected, the dentist may perform a root canal. This is a procedure in which the pulp is removed from the root, which is the part of the tooth that anchors it to the gums. The empty space is then cleaned and filled with a special material. The root and the tooth stay in place, but the tooth structure is not as strong as before. To shore it up, the person may need a crown.

* anesthetic (an-es-THET-ik) is a medicine that deadens the sensation of pain,

How Can Cavities Be Prevented?

People can take several steps to stop most cavities. They can brush twice a day and floss every day. Brushing and flossing help remove plaque. They can use a soft-bristled toothbrush. People should pick a brush that feels comfortable and will reach all the teeth, even those in back. They should replace the toothbrush when the bristles show signs of wear. People should use a toothpaste that contains fluoride, a mineral that helps protect against tooth decay. To clean the teeth, they should brush with a short, gentle, back-and-forth motion. People should not forget the inside surfaces, the back teeth, and the tongue. They should floss to reach plaque between the teeth and under the gum line, where a brush cannot go. Finally, people should cut down on sweets and between-meal snacks. Damaging acid forms in the mouth each time a person eats a sugary or starchy food. The acid continues to affect the teeth for at least 20 minutes afterward. The more often people eat these kinds of food, the more times they feed the bacteria that cause cavities. In addition, some sugary foods do more harm than others. Sticky or chewy sweets may cling to the teeth, staying in the mouth and causing problems longer than other foods.

People should see their dentist regularly for checkups and cleanings. Dentists may apply extra fluoride (FLOOR-eyed) in the form of a gel, foam, or rinse. In addition, dentists may apply dental sealants, thin plastic coatings that are put on the chewing surface of back teeth. Such sealants are painted on as a liquid, but they quickly harden to form a shield over the teeth that keeps out the food and bacteria that cause decay. Dentists say that children should get sealants on their permanent back teeth as soon as they come in. In some cases, sealants are also put on baby teeth or on the teeth of teenagers or adults.

A Flurry of Fluoridation

Fluoride is a mineral that occurs naturally in all water sources. Many areas, especially in the southern states, have a water supply that is well fluoridated naturally.

Scientists as far back as the early 1900s noted fluoride's role in preventing tooth decay. Fluoride can even reverse the early decay process. Since the 1940s, some communities in areas where natural fluoride is low have been adding extra fluoride to their water. This is a very effective and inexpensive way to help prevent cavities on a large scale.

Today, about 60 percent of the U.S. water supply is fluoridated. In places where the water is not fluoridated, or in families who drink unfluoridated bottled water instead of tap water, dentists may prescribe fluoride supplements for children.

See also
Bacterial Infections
Gum Disease



Smith, Rebecca W The Columbia University School of Dental and Oral Surgery's Guide to Family Dental Care. New York: W. W Norton, 1997.


American Dental Association, 211 East Chicago Avenue, Chicago, IL 60611. The leading national organization for dentists has information about tooth decay and dental care on its website.
Telephone 312-440-2500

U.S. National Institute of Dental and Craniofacial Research, 31 Center Drive, MSC 2290, Bethesda, MD 20892-2290. Part of the U.S. National Institutes of Health (NIH), this agency provides information on tooth decay and dental care.
Telephone 301-496-4261

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