title: Immediate effects of rapid maxillary expansion with Haas-type and hyrax-type expanders: a randomized clinical trial.
abstract: BACKGROUND
  The purposes of this study were to evaluate and compare the immediate effects of rapid maxillary expansion (RME) in the transverse plane with Haas-type and hyrax-type expanders by using cone-beam computed tomography.
  
  
  METHODS
  A sample of 33 subjects (mean age, 10.7 years; range, 7.2-14.5 years) with transverse maxillary deficiency were randomly divided into 2 groups: Haas (n = 18) and hyrax (n = 15). All patients had RME with an initial activation of 4 quarter turns followed by 2 quarter turns per day until the expansion reached 8 mm. Cone-beam computed tomography scans were taken before expansion and at the end of the RME phase. Maxillary transversal measurements were compared by using the mixed analysis of variance (ANOVA) model and the Tukey-Kramer method.
  
  
  RESULTS
  RME increased all maxillary transverse dimensions (P <0.0001). There was less expansion at skeletal than dental levels. The hyrax group had greater statistically significant orthopedic effects and less tipping tendency of the maxillary first molars compared with the Haas group.
  
  
  CONCLUSIONS
  Both appliances were efficient in correcting a transverse maxillary deficiency. The pure skeletal expansion was greater than actual dental expansion. The hyrax-type expander produced greater orthopedic effects than did the Haas-type expander, but this effect was less than 0.5 mm per side and might not be clinically significant.
authors: Department of Orthodontics, Pontifical Catholic University of Rio Grande Do Sul, Porto Alegre, Rio Grande do Sul, Brazil. andre5051@hotmail.com
authors: André
authors: A
authors: Weissheimer
authors: Luciane Macedo
authors: LM
authors: de Menezes
authors: Mauricio
authors: M
authors: Mezomo
authors: Daniela Marchiori
authors: DM
authors: Dias
authors: Eduardo Martinelli Santayana
authors: EM
authors: de Lima
authors: Susana Maria Deon
authors: SM
authors: Rizzatto
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D002508:Cephalometry; D002648:Child; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008437:Maxilla / Q000000981:diagnostic imaging*; D016382:Orthodontic Appliance Design; D010155:Palatal Expansion Technique / Q000295:instrumentation*; D011446:Prospective Studies; D018709:Statistics, Nonparametric; D016896:Treatment Outcome