Profession concerned with the teeth and mouth. It includes repair or removal of decayed teeth, straightening and adjustment of teeth for proper occlusion, and design, manufacture, and fitting of false teeth and other prosthetic devices. X-rays are used to show conditions not visible on examination. Using local anesthesia, caries in teeth are drilled to remove diseased areas and filled with various materials. Decay that reaches a tooth's root risks infection of the nerve and requires root-canal surgery. Teeth that must be extracted are replaced by crowns for single teeth and full or partial dentures or implants for more. Dentists also educate patients on oral hygiene, examine and clean teeth, and apply fluoride compounds for decay resistance.