A para-functional habit or parafunctional habit is the habitual exercise of a body part in a way that is other than the most common use of that body part. In dentistry, orthodontics, and oral and maxillofacial pathology, the body part in question is usually the mouth, tongue, or jaw. Oral para-functional habits may include bruxism, tongue tension, fingernail biting, pencil or pen chewing, mouth breathing, and any other habitual use of the mouth unrelated to eating, drinking, or speaking.