A condition in which a tooth fails to fully grow out (erupt) from the gums. Impacted teeth usually occur because of crowding or lack of space in the bone. Third molars (wisdom teeth), particularly the lowers, are the last to erupt and are more likely to be impacted. Because of crowding and difficulty with cleaning, decay in adjacent teeth, as well as gum disease, often occurs. Surgical removal of impacted teeth is often recommended, but may be optional unless problems develop.