title: [The preliminary study of the treatment timing for rapid maxillary expansion].
abstract: OBJECTIVE
  The aim of this study was to find the treatment timing of rapid maxillary expansion by investigating the relationship among the chronologic age, dental age, skeletal age and treatment effect of rapid maxillary expansion.
  
  
  METHODS
  A sample of thirty patients who required rapid maxillary expansion was selected. The patients ranged in age from 11 to 14 years, with the mean age being 12.30 years. Assessment of the skeletal age was made with a hand radiograph before treatment. The posteroanterior cephalograms, occlusal radiograph of the maxilla were taken at the time of pretreatment and post-treatment. Paired t test and multiple regression analysis were used for statistical analysis.
  
  
  RESULTS
  The results showed that the effects of rapid maxillary expansion were different even though the chronologic ages were similar. A negative correlation was found between the skeletal age and the expansive effect. Regressive coefficient was -6.440, P value was 0.045. There was a significant negative correlation between the dental age and the expansive effect. The regressive coefficient was -1.289, P value was 0.000. The expansive effect was on the decrease while the second maxillary molars erupted continuously.
  
  
  CONCLUSIONS
  It is proposed that rapid maxillary expansion could be used successfully before the second maxillary molars erupt. The optimal orthopedic effect could be attained.
authors.affiliation: Department of Orthodontics, College of Stomatology, Ninth People's Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200011, China. gongymingi@yahoo.com.cn
authors.forename: Jing
authors.initials: J
authors.lastname: Lu
authors.forename: Fang-fang
authors.initials: FF
authors.lastname: Gong
authors.forename: Gang
authors.initials: G
authors.lastname: Shen
mesh_terms: D000293:Adolescent; D000365:Age Determination by Skeleton; D000366:Age Determination by Teeth; D002508:Cephalometry; D002648:Child; D006801:Humans; D008437:Maxilla; D008445:Maxillofacial Development; D008963:Molar / Q000254:growth & development; D010155:Palatal Expansion Technique; D061665:Time-to-Treatment; D014078:Tooth Eruption