title: The effectiveness of the Invisalign appliance in extraction cases using the the ABO model grading system: a multicenter randomized controlled trial.
abstract: OBJECTIVE
  The aim of this study was to assess treatment outcomes of the Invisalign and compare results with braces.
  
  
  METHODS
  One hundred and fifty-two adult orthodontic patients, referred to two Orthodontic Specialist Clinics, were randomized to receive either invisalign or brace treatment. All patients were evaluated by using methods from the American Board of Orthodontics Phase III examination. The discrepancy index was used to analyze pretreatment records to control for initial severity of malocclusion. The objective grading system was used to systematically grade posttreatment records. The Wilcoxon 2-sample tests were used to evaluate treatment outcome of Invisalign and braces.
  
  
  RESULTS
  The total mean scores of the objective grading system categories were improved after treatment in both groups. The improvements were not statistically significant in scores for alignment, marginal ridges, occlusal relations, over jet, inter-proximal contacts, and root angulation. Invisalign scores were consistently lower than braces scores for buccolingual inclination and occlusal contacts.
  
  
  CONCLUSIONS
  The overall improvement in OGS scores indicate that both Invisalign and fixed appliances were successful in treating Class I adult extraction cases in this sample.
authors.affiliation: The Second Affiliated Hospital Zhejiang University School of Medicine Hangzhou, China.
authors.forename: Weihong
authors.initials: W
authors.lastname: Li
authors.affiliation: The Second Affiliated Hospital Zhejiang University School of Medicine Hangzhou, China.
authors.forename: Shimei
authors.initials: S
authors.lastname: Wang
authors.affiliation: The Second Affiliated Hospital Zhejiang University School of Medicine Hangzhou, China.
authors.forename: Yanzhen
authors.initials: Y
authors.lastname: Zhang
keywords: ABO model grading system; invisalign; orthodontic; randomized controlled trial