Palatal expander
（重定向自Palate expander）
A palatal expander, also known as a rapid palatal expander, rapid maxillary expansion appliance, palate expander, orthodontic expander, Haas, or Hyrax, is used to widen the upper jaw (maxilla) so that the bottom and upper teeth will fit together better. This is a common orthodontic procedure. Although the use of an expander is most common in children, it can be and has successfully been used in adults, although the effects of expansion are slightly more uncomfortable. Also, depending on the amount of correction and age of the patient, it may result in surgical separation of the maxilla. Use of a palatal expander is most often followed by braces to straighten out all the teeth now that room has been created.