Dental caries, also described as tooth decay, is an infectious disease which damages the structures of teeth. The disease can lead to pain, tooth loss, infection, and, in severe cases, death. There is a long history of dental caries, with evidence showing the disease was present in the Bronze, Iron, and Medieval ages but also prior to the neolithic period. The largest increases in the prevalence of caries have been associated with diet changes.Today, it remains one of the most common diseases throughout the world.

There are numerous ways to classify dental caries. Although the presentation may differ, the risk factors and development among distinct types of caries remain largely similar. Initially, it may appear as a small chalky area but eventually develop into a large, brown cavitation. Though sometimes caries may be seen directly, radiographs are frequently needed to inspect less visible areas of teeth and to judge the extent of destruction.

Tooth decay is caused by certain types of acid-producing bacteria which cause damage in the presence of fermentable carbohydrates such as sucrose, fructose, and glucose. The resulting acidic levels in the mouth affect teeth because a tooth's special mineral content causes it to be sensitive to low pH. Specifically, a tooth  is in a constant state of back-and-forth demineralization and remineralization between the tooth and surrounding saliva. When the pH at the surface of the tooth drops below 5.5, demineralization proceeds faster than remineralization . This results in the ensuing decay.

Depending on the extent of tooth destruction, various treatments can be used to restore teeth to proper form, function, and aesthetics, but there is no known method to regenerate large amounts of tooth structure. Instead, dental health organizations advocate preventative and prophylactic measures, such as regular oral hygiene and dietary modifications, to avoid dental caries.