MODEL RELEASED. Dental drilling. Drill being used in a patient's mouth. The drill is being used to remove areas of decayed tooth (black). The space will then either be filled in with a dental filling, or the tooth will be drilled down even further so a cap (an artificial tooth) can be fitted. The drill head is seen next to one of the pre-molars. Next to it is a canine, and at the front of the mouth are the incisors. Tooth decay (dental caries) is caused by bacteria feeding on food debris in the mouth, producing acids that lead to erosion of the tooth enamel.