Caries and cavities are common names for tooth decay. Human teeth are protected by an external enamel which is the hardest tissue in the body, and thereby protects the teeth from sensitivity and teeth cavities. It is composed of minerals to an extent of 96% with the rest being water and organic matter. Hydroxyapatite, a crystalline form of calcium phosphate is the major mineral constituent. Our teeth are all the time covered with saliva which is also rich in the same minerals, and has a basic nature with pH close to 7. In this state a two way equilibrium chemical process exists between minerals in the enamel and those in the saliva. If the prevailing pH around the teeth goes acidic, the equilibrium shifts, and more minerals pass from the enamel to saliva than from saliva to enamel.

Sugars and carbohydrates present in food bits which remain sticking to the teeth are converted by bacteria to acid. The more time these bacteria get to act, the greater is the amount of acid produced. This acid will be more concentrated in pits and fissures of molars, in spaces around the gum line, and interdental spaces. As enamel becomes deficient in minerals, it becomes porous in those spots. If the process continues, very tiny local pits are created in the enamel. These only aid the process of demineralization by trapping food and allowing acid production. This process detected in time can be checked, and may even be reversed in early stages by the use of fluorides. If the decay is allowed to continue unchecked, acid can cause holes in the enamel.

Teeth may become sensitive to hot and cold; and sweet things. That is caries in the early stage. If the cavity created by this process goes deep enough it can affect the pulp,  and cause infection and severe pain which must be treated with the help of a root canal treatment. Caries can also be caused under the gum line.

Symptoms of caries are, sensitivity to hot and cold, continuous and sever pain when chewing and development of white spots. During a dental visit caries can be confirmed by x-ray images. Enamel will appear white while decayed regions will show darker. Some dentists may use lasers to detect caries. This method could detect caries in the very early stages.

Caries can be prevented best by maintaining good oral hygiene (regular and frequent brushing and flossing), avoiding junk food and food with sugar and starch, and use of antibacterial mouth washes. A very good practice in some Muslim countries is to brush (or at least rinse) after every food intake or drink. Use of fluorides and chewing gum containing xylitol will also help. Use of sealants is another option.

Treatment at very early stages is possible with fluorides. But once enamel is damaged it cannot be restored. The treatment lies in filling, and if the damage is too much, root canal treatment may be needed. In case of extreme neglect an extraction may be the only option.