Dental caries is the medical term for tooth decay or cavities. It is caused by acid erosion of tooth enamel.

Many different types of bacteria normally live in the human mouth. They build up on the teeth (along with saliva, bits of food and other natural substances) in a sticky film called plaque. Plaque forms especially easily in certain places. These include:

Some of the plaque bacteria convert sugar and carbohydrates (starches) in the foods we eat into acids. These acids dissolve minerals in the surface of the tooth. This erodes the enamel or creates pits in it that are too small too see at first. But they get larger over time.

The damage can occur anywhere the tooth is exposed to plaque and acid. This includes the hard outer enamel on the tooth crown or parts of the root that have been exposed because of receding gums. Once decay penetrates the protective enamel, it can enter the softer, vulnerable dentin. This is the main body of the tooth. A cavity can even penetrate the soft tooth pulp and the sensitive nerve fibers within it.

No one really knows what causes the pain people get with cavities. Theories include:

Treatment - The standard treatment for a cavity is to fill the tooth. First, the dentist will numb the area. Then the decayed material in the cavity is removed and the cavity is filled. Fillings usually are made of dental amalgam or composite resin. Amalgam is a silver-gray material made from silver alloyed with copper or other metals to make it more durable. Composite resin offers a better appearance because it is tooth-colored.

Amalgams are used primarily in molars and premolars. Resins are used primarily in the front teeth, although it is possible to use them in all teeth. Gold inlay may be used if greater strength is needed, but this is more expensive.

If a cavity is large, the remaining tooth may not be able to support the amount of filling material that would be needed to repair it. In this case, the dentist will remove the decay, fill the cavity, and cover the tooth with an artificial crown.

Sometimes the part of the tooth you can see remains relatively intact, but there is damage inside the tooth. In these cases, the dentist may refer you to a dental specialist called an an endodontist for root canal treatment. In this procedure, the endodontist removes the tooth's pulp and replaces it with an inert material. In most cases, the tooth's natural crown will need to be replaced with an artificial crown.