Infection: Tooth Decay

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Infection: Tooth Decay

Causes and Symptoms
The Future
For more information


Tooth decay, also known as dental caries, is a disorder of the mouth in which bacteria living in the mouth break down carbohydrates in food. The bacteria produce acids that eat away at the enamel—the hard smooth outer surface of the tooth—eventually producing cavities in the enamel. If untreated, cavities can lead to toothache, loss of the tooth, and bacterial infections spreading to the gums and other tissues.


Tooth decay begins with plaque, a thin film that is a mixture of saliva, bacteria, and dead cells from the tissues that line the mouth. When a person eats foods rich in carbohydrates—sugary or starchy foods—the bacteria in the plaque ferment the sugars in these foods, forming lactic acid. Plaque builds up on teeth if it is not removed by regular flossing and brushing, eventually hardening into a whitish substance called tartar.

The surfaces of human teeth are basically composed of minerals that are sensitive to acid. Under normal circumstances, minerals lost from the tooth surface are replaced by the saliva. But when plaque is not removed from the teeth by brushing or flossing, the acid formed by the bacteria begins to remove enamel from the surface of the tooth faster than the

saliva can restore it. At this point the surface of the tooth begins to develop small pits or cavities. If these are not attended to, they can grow larger and move inward to affect the dentin, a layer of hard tissue below the enamel. Dentin is softer than enamel and protects the pulp at the center of the tooth. When the cavity cuts through the enamel into the dentin, it speeds up the decay process. The pulp contains nerve endings that become inflamed when the bacteria from the mouth are able to gain entry.

Once the tooth decay reaches the pulp, the person may experience pain when biting down on food or the more severe toothache. If the inflammation has spread to affect the jawbone underlying the tooth, the person may develop a pus-filled hollow known as an abscess. In extreme cases, the bacteria may spread to other parts of the face or enter the bloodstream and spread infection to other parts of the body.


Tooth decay is one of the most common health problems around the world. It is also one of the oldest. Prehistoric humans appear to have had dental problems dating from the time that they first began to cultivate grains for food, since bread and flour are rich in carbohydrates. Skulls found in Asia dating from 7000 BCE have teeth that contain holes created by early dental drills. Ancient Egyptian, Indian, and Sumerian medical

texts attributed tooth decay and cavities to a “tooth worm.” The rate of tooth decay among humans increased rapidly after 1850 CE, when people began to eat larger quantities of refined sugar, refined flour, and other sweet and sticky foods.

According to the Centers for Disease Control and Prevention (CDC), tooth decay is the most common chronic health disorder among children in the United States between the ages of five and seventeen. Fifty-nine percent of children in this age group have one or more cavities. Many adults also have untreated tooth decay—27 percent of those between the ages of thirty-five and forty-four, and 30 percent of those over sixty-five.

Worldwide, about 90 percent of schoolchildren and 95 percent of adults have had at least one dental cavity. The rates are highest in Asia and Latin America and lowest in Africa. Males and females are equally likely to develop tooth decay.

In developed countries, the rates of dental cavities have dropped since the 1950s; this decrease is attributed to improved patient education about care of the mouth and teeth, and to such preventive practices as adding fluoride to the water supply. On the other hand, however, the reduction in the number of cavities is not equally distributed throughout the population. Studies in Western Europe, Canada, and the United States indicate that 20 percent of the population in these countries has 70 percent of the cavities.

The Dentist Who Discovered the Cause of Tooth Decay

The bacterium that causes tooth decay was identified in the early 1920s by military dentist Fernando Rodríguez Vargas (188–1932). Born in Puerto Rico, Rodríguez Vargas graduated from the dental school of Georgetown University in Washington, D.C. in 1913. He began to investigate the cause of tooth decay in 1915 while working for the federal government's Indian Medical Service in Tucson, Arizona. There he noticed that the Native Americans he was treating had badly discolored teeth as well as a high number of cavities. His early research was interrupted when the United States entered World War I in 1917, and he was sent overseas to examine and treat American soldiers for dental problems.

In 1921, Rodríguez Vargas was working as a bacteriologist in Washington, D.C., for the Army Dental Corps when he discovered that three species of Lactobacillus bacterium are responsible for producing the acids that cause tooth decay. He published his findings in a military medical journal. In 1928 he wrote an article for the Journal of the American Medical Association on the usefulness of various antiseptics in cleansing the mouth and preventing tooth decay.

Rodríguez Vargas died of pneumonia in 1932. He has been honored for his pioneering work in dentistry by the Walter Reed Army Institute of Research and the Puerto Rico College of Dental Surgeons.

People at increased risk of tooth decay include:

  • Babies who are given sweetened juices or other liquids to drink. “Baby bottle tooth decay” is a common pattern of cavities in the front of the mouth found in very young children.
  • People who abuse methamphetamine, an addictive stimulant drug. Methamphetamine dries out the tissues of the mouth, contributing to outright tooth loss as well as tooth decay.
  • People with diabetes or Sjögren syndrome. These disorders reduce the amount of saliva in the mouth.
  • People with eating disorders. People with bulimia who force themselves to vomit repeatedly weaken the enamel on their teeth by exposing the tooth surfaces to stomach acids.
  • Smokers. Smoking causes the gums to recede, thus exposing more of the tooth surface to bacteria in the mouth and the acid they produce.

Causes and Symptoms

Tooth decay is caused by acid-forming bacteria in the mouth that live in plaque that has not been removed from the surfaces of the teeth. Decay is more likely to affect the teeth in the back of the mouth (the molars and premolars). These teeth have pits and grooves on their upper surfaces that make it more difficult to remove plaque completely.

Tooth decay can develop over a period of months or even years without any obvious symptoms. When the decay begins to affect the dentin or the pulp beneath the enamel, however, the patient may begin to notice such symptoms as:

  • Sensitivity when eating or drinking sweet, very hot, or very cold foods
  • Pain when biting on something firm or tough
  • Pus around a tooth, which indicates that at abscess has formed
  • Pain that lasts after the person has finished eating
  • Visible pits or holes in the tooth
  • Bad breath or a bad taste in the mouth
  • Intense toothache


The diagnosis of tooth decay is made by a dentist rather than a primary care doctor in most cases. The dentist will ask the patient about tooth sensitivity or pain. In some cases he or she can see signs of tooth decay just by looking inside the patient's mouth with an angled mirror. Another tool that is used is

a hook-shaped instrument called an explorer, which allows the dentist to probe soft spots or areas of discoloration in the teeth. Last, the dentist will take x-ray films of the patient's mouth to get a clearer picture of whether and how far the areas of decay have penetrated the tooth.


The treatment of tooth decay depends on the extent and severity of the problem. If the decay has just begun, the dentist may apply a solution of fluoride to stop the decay process. If the decay has progressed further, the dentist may need to drill away the decayed material or even remove the tooth.

A small area of tooth decay is filled with a silver alloy, a composite resin, gold, or porcelain. Dentists call a filling a dental restoration. If much of the tooth must be removed, the dentist will drill away the top of the tooth and replace it with what is called a crown or a cap. If the tooth decay has affected the pulp in the center of the tooth and destroyed the nerve endings, the dentist removes the pulp along with any decayed portions of the tooth and fills the center of the tooth with a sealing material. This procedure is called a root canal.

If the tooth is badly decayed, was broken in an accident, or is likely to cause trouble in the future, the dentist will perform an extraction. The tooth is lifted with a tool called an elevator and removed from its socket with dental forceps. The dentist will apply a material called gelfoam to speed clotting, or close up the socket with sutures if the wound is large. The patient is given antibiotics to take for several days to prevent infection.


The prognosis of tooth decay depends on the stage at which it is discovered and treated. Dental fillings usually last for years with proper care, although they often need replacement when the patient is middle-aged. It is rare for tooth decay to lead to serious complications other than the loss of teeth; however, in a few cases bacteria from a tooth abscess can spread to the tissues of the floor of the mouth or to a hollow space within the brain that lies behind the upper jaw. These infections are potentially life-threatening.


Tooth decay is one of the most easily prevented health problems. There are several known ways to lower the risk of dental cavities:

  • Brushing the teeth after each meal or snack and using dental floss once a day. Brushing is important because plaque starts to form within twenty minutes of finishing a meal. Flossing helps to remove food particles trapped between teeth.
  • Limiting sweets and sugary drinks like soda or sweetened tea.
  • Quitting smoking.
  • Using a toothpaste that contains fluoride or having the dentist apply a fluoride solution to the teeth during a checkup. Fluoride is a chemical that helps to prevent tooth decay by protecting the minerals in tooth enamel. According to the CDC, people in communities that have added fluoride to their drinking water have 29 percent fewer cavities.
  • Sealants. Sealants are protective plastic coatings applied to the surfaces of the back teeth that are most likely to develop cavities. They need to be replaced every few years.
  • Antibacterial mouthwashes. Dentists sometimes recommend these for people who are vulnerable to tooth decay because of their medical conditions.
  • Having regular dental checkups and necessary treatments.

The Future

Newer methods for the prevention of tooth decay include the use of argon lasers to remove early signs of the erosion of tooth enamel and the development of a vaccine against tooth decay. Clinical trials for such a vaccine started in May 2006, but the vaccine has not yet been approved for use.


Abscess: A collection of pus that has formed in a body cavity or hollow.

Caries: The medical name for tooth cavities.

Dentin: A firm tissue that lies between the enamel and the pulp of a tooth.

Enamel: The hard, smooth, white outer surface of a tooth.

Plaque: A film that forms on the surface of teeth containing bacteria, saliva, and dead cells.

Pulp: The soft living material in the center of a tooth that contains blood vessels and nerve endings.

Tartar: Hardened plaque.

SEE ALSO Bulimia; Periodontal disease; Sjögren syndrome

For more information


Kemper, Bitsy. Out and About at the Dentist. Minneapolis, MN: Picture Window Books, 2007.

Mestman, Sadie S., and Ariella D. Herman. What to Do for Healthy Teeth: Easy to Read, Easy to Use. La Habra, CA: Institute for Healthcare Advancement, 2004.

Sutton, Amy L., ed. Dental Care and Oral Health Sourcebook. Detroit, MI: Omnigraphics, 2003.


American Dental Association (ADA). Tooth Decay (Cavities/Caries). Available online at (updated January 2008; accessed August 23, 2008).

Centers for Disease Control and Prevention (CDC). Preventing Dental Caries. Available online at (updated November 25, 2005; accessed August 23, 2008).

KidsHealth. What's a Cavity? Available online at (updated April 2008; accessed August 23, 2008).

Mayo Clinic. Cavities/Tooth Decay. Available online at (updated April 27, 2007; accessed August 23, 2008).

National Institute of Dental and Craniofacial Research (NIDCR). Plaque: What It Is and How to Get Rid of It. Available online in PDF format at (accessed August 23, 2008).

National Maternal and Child Oral Health Resource Center. What Is Tooth Decay? Available online at (accessed August 23, 2008). This is a Flash animation about tooth decay; click on icon at right to start the animation.

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Infection: Tooth Decay

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