When plaque or tartar builds up on a tooth, it can begin to rot away the enamel. Dentists and other medical professionals know these decayed spots as caries. You know them as cavities. Lack of proper dental hygiene, such as infrequent brushing and flossing or irregular cleanings by a dentist, can all lead to the buildup of plaque and tartar, as well as the bacteria associated with food and your salvia. Though many cavities are caught while small and painless, a cavity left to fester can become extremely painful, as it can quickly penetrate down to the root of the tooth.