A cavity happens when bacteria in the mouth produces acid that attacks your teeth. Over time, this acid can dissolve away the tooth enamel and cause a hole, or cavity. Unlike some other diseases or injuries, a cavity will not heal by itself, but if the early signs of dental decay are promptly treated before a cavity forms, it can be stopped or even reversed by your dentist and your home care. To prevent dental disease: brush twice a day, floss once a day, eat a balanced diet, limit eating and drinking between meals, and visit your dentist regularly.