title: [Effect of repetitive rapid palatal expansions and constrictions by double hinged expander in maxillary protraction cases].
abstract: OBJECTIVE
  To investigate the benefits of repetitive rapid palatal expansions/constrictions therapy using double hinged expander over rapid palatal  expansion alone with Hyrax expander in maxillary protractions cases and to discuss the indications of the combination therapy.
  
  
  METHODS
  Thirty four  children with retrognathic maxilla were selected and randomly divided into two treatment groups. Eighteen children were in group A and received maxillary  protraction with Hyrax expander rapid palatal expansion alone. Sixteen children were in group B and received maxillary protraction with double hinged  expander repetitive rapid palatal expansions/constrictions combin therapy. Cephalometric analysis was done to compare the pre and post-treatment  lateral cephalograms.
  
  
  RESULTS
  Significant difference in forward movement of maxilla (P<0.05)were observed between group B [A-Np increased  2.53 mm, A-vertical line (A-VRL) increased 2.78 mm] and group A (relatively 1.86 mm and 2.01 mm). Significant difference in soft tissue backward  movement of mandible (P<0.05)were also observed between group A (LLC-VRL decreased 2.82 mm) and group B (relatively 1.63 mm).
  
  
  CONCLUSIONS
  Repetitive rapid palatal expansions/constrictions using double hinged expander resulted in more maxilla forward movement compared with Hyrax rapid  palatal expansion alone in maxillary protraction cases.
authors: Department of Orthodontics, Peking University School, Beijing, China.
authors: Wei-tao
authors: WT
authors: Liu
authors: Yan-heng
authors: YH
authors: Zhou
mesh_terms: D000293:Adolescent; D002648:Child; D005115:Extraoral Traction Appliances; D005260:Female; D006801:Humans; D008297:Male; D008313:Malocclusion, Angle Class III / Q000000981:diagnostic imaging / Q000628:therapy*; D008437:Maxilla / Q000473:pathology; D010155:Palatal Expansion Technique / Q000295:instrumentation*; D011859:Radiography