title: [Analysis of the efficacy of Twin-block appliance on maxillofacial growth of six pairs of monozygotic twins].
abstract: OBJECTIVE
  The purpose of this study was to investigate the efficacy of Twin-block appliance on maxillofacial growth by using monozygotic twins.
  
  
  METHODS
  6 pairs of non-high angle monozygotic twins aged 12.2 with class II division 1 malocclusion were selected from 32 pairs of twins. In the first year Twin A of each pair was functionally treated using Twin-block appliance; meanwhile, Twin B underwent non-extracted fixed treatment without any treatment procedure which might cause changes like functional appliances such as Class II elastics. The difference of the cephalometric changes of maxilla and mandible before and after treatment between Twin A and Twin B was compared using paired-t test.
  
  
  RESULTS
  Compared with those of Twin A after one year treatment, SNA, Cd-A and Cd-Go of Twin B had little chang (P>0.05), but Cd-S' reduced (P<0.05), Cd-Gn and SNB increased (P=0.01), (Cd-Gn)-(Cd-A) and ANB increased (P<0.05) significantly.
  
  
  CONCLUSIONS
  Twin-block appliance can stimulate forward mandibular growth and cause forward mandibular displacement, but has little effect on ramus height and maxillary growth.
authors.affiliation: Department of Orthodontics, Ninth People's Hospital, School of Stomatology, Shanghai Second Medical University, Shanghai 200011, China. gpji@hotmail.com
authors.forename: Guo-ping
authors.initials: GP
authors.lastname: Ji
authors.forename: Xiao-gang
authors.initials: XG
authors.lastname: Pan
authors.forename: Gang
authors.initials: G
authors.lastname: Shen
authors.forename: Ning
authors.initials: N
authors.lastname: Huang
mesh_terms: D002508:Cephalometry; D006801:Humans; D008312:Malocclusion, Angle Class II / Q000628:therapy*; D008334:Mandible / Q000254:growth & development*; D008437:Maxilla / Q000254:growth & development*; D017289:Orthodontic Appliances, Functional; D014430:Twins, Monozygotic