Cavities, also called dental caries (KARE-eez), are areas of tooth decay caused by bacteria.

Michael's Story

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 he felt a little twinge of pain now and then when he ate ice cream, his favorite food, Michael had not paid much attention to the feeling. He would not have known that he had a cavity if he had not gone to the dentist for a regular checkup. Once the cavity was discovered, the dentist drilled out the decay and filled 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.

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.

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.
Illustration by Frank Forney. © 2016 Cengage Learning®.

What Are Cavities?

Cavities are areas of decay on the teeth that are caused by bacteria * . Cavities are one of the most common human diseases. Nevertheless, 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 between 200 and 300 types of bacteria, although only a few are involved in creating cavities. The bacterium that causes cavities most often is Streptococcus mutans (strep-to-KOK-us MUtanz), although a few other species also play a role. Streptococcus mutans can change the sugars and starches in food into lactic acid in less than one minute. The bacteria and lactic acid combine with mucus * and food particles, forming a sticky mass called plaque (PLAK) that sticks to teeth. If not removed, plaque hardens on the teeth.

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.

Who Gets Cavities?

Anyone can develop a cavity. They are most common in children, young adults, and the elderly. People who eat a diet high in sugary and starchy foods have a higher risk of developing cavities, since the more sugar and starch people eat, the more cavity-causing acid they make. People who already have many fillings have an increased risk as well, since the area around fillings is an ideal spot for decay to start. At least 28 percent of preschool-age children have one or more cavities, most of which go untreated because many parents believe incorrectly that cavities in baby teeth are not serious. The situation is not much better in people with permanent teeth. According to the U.S. Centers for Disease Control and Prevention (CDC), in 2013, 17.5 percent of children ages 5 to 19 had untreated cavities as did 27.4 percent of adults ages 20 to 44.

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 small and hard to see. Treating cavities early can prevent later pain and tooth loss.

When 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 * before drilling. The decayed material is then replaced with a filling. Fillings can be made from a number of materials. The most common is silver amalgam (a-MAL-gam), a mixture of silver and other metals, which is used mainly in back teeth. For cosmetic reasons, fillings on front teeth are usually made of other materials that match the color of the teeth.

Sometimes decay is so extensive that removing it all leaves the tooth weak and more susceptible to breaking. In that case, the dentist may fit the person with a crown, which is 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 or oral surgeon may perform a root canal. In this procedure, 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 strengthen it, the person may need a crown.

A Flurry of Fluoridation

Fluoride is a mineral that occurs naturally in water sources. Many areas, especially in the southern United States, have a water supply that is fluoridated naturally. In other areas, fluoride may be added to the water supply.

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 small amounts of fluoride to their water. This is a very effective and inexpensive way to help prevent cavities on a large scale, although in some communities the addition of fluoride is controversial.

As of 2013, about 75 percent of the U.S. public water supply was fluoridated. In places where the water is not fluoridated, or in families who drink well water or unfluoridated bottled water instead of tap water, dentists may prescribe a fluoride supplement in the form of a small pill for children. Too much fluoride can cause tooth discoloration, so people should discuss appropriate fluoride use with their dentists.

How Can Cavities Be Prevented?

People can take several steps to prevent cavities. They can brush twice a day and floss every day. Brushing and flossing help remove plaque before it hardens on the tooth. People should use a soft-bristled toothbrush that feels comfortable and will reach all the teeth, even those in back. Battery operated or electric toothbrushes may be more effective than brushing by hand. The toothbrush should be replaced whenever the bristles show signs of wear, usually every three to four months.

The introduction of small amounts of fluoride (FLOOR-eyed) into the water supply can reduce cavities in children and young adults by 30 to 50 percent. Fluoride is a mineral that helps strengthen teeth and protect against tooth decay. Fluoride is also added to some toothpastes and mouthwashes.

Tooth brushing should start as soon as a baby's first tooth is visible. Brushing with a short, gentle, back-and-forth motion for two minutes is recommended. Some children's toothbrushes play a song, and children should brush for as long as the song plays, making sure to reach the inside surfaces, the back teeth, and the tongue. Regular use of dental floss can reach plaque between the teeth and under the gum line where a brush will not fit. Young children will need assistance to brush and use floss correctly. Finally, people should limit sweets and sticky carbohydrates such as potato chips between meals. 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 after the food is swallowed. The more often people eat, 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, usually twice a year, for checkups and cleanings. Dentists may recommend dental sealants. Sealants are thin plastic coatings that are put on the chewing surface of back teeth. They are painted on as a liquid but quickly harden to form a shield over the teeth that keeps out food and bacteria that cause decay. Dentists recommend that children 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.

See also Abscesses • Bacterial Infections • Mouth Disorders: Overview



Horne, Steven B. “Dental Cavities (Dental Caries).” (accessed March 23, 2016).

Mayo Clinic Staff. “Cavities/Tooth Decay.” Mayo Foundation for Medical Education and Research. (accessed March 23, 2016).

Merck Manual Consumer Version. “Cavities.” (accessed March 23, 2016).

National Institute of Dental and Craniofacial Research. “The Tooth Decay Process: How to Reverse It and Avoid a Cavity.” (accessed March 23, 2016).


American Dental Association. 211 East Chicago Ave., Chicago, IL 60611-2678. Telephone: 312-440-2500. Website:

* bacteria (bak-TEER-ee-a) are single- celled microorganisms. Some, but not all, types of bacteria can cause disease in humans. Many types live in the body without causing harm, and several digestive system bacteria are actually beneficial.

* mucus (MYOO-kus) is a thick, slippery substance that lines the insides of many body parts.

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

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)