title: Linear measurements using virtual study models.
abstract: OBJECTIVE
  To perform a systematic review of the literature to assess the reliability and validity of linear measurements using virtual vs plaster study models.
  
  
  METHODS
  A search strategy was developed for four online databases, and references were further hand searched for studies additional papers. Three researchers determined the eligibility of papers by applying specific selection criteria and ultimately selected 17 papers. Grouped by virtual model acquisition type and the number of landmarks used in a given measurement, the data were weighted by sample size and analyzed in terms of the reliability and validity of linear measurements.
  
  
  RESULTS
  The intrarater reliability was high for two-landmark and >two-landmark linear measurements performed on laser-acquired models or cone-beam computed tomography (CBCT)-acquired models and were similar to measurements on plaster models. Validity was high for two-landmark and >two-landmark linear measurements comparing laser-acquired models or CBCT-acquired models to plaster study models, and the weighted mean differences were clinically insignificant. Agreement of measurements was excellent, with less variability than correlation. Acquisition type had no perceived influences on reliability and validity. More than two-landmark measures tended to have higher mean differences than two-landmark measures.
  
  
  CONCLUSIONS
  Virtual study models are clinically acceptable compared with plaster study models with regard to intrarater reliability and validity of selected linear measurements.
authors.affiliation: Orthodontic Graduate Program, School of Dentistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Canada.
authors.forename: Nghe S
authors.initials: NS
authors.lastname: Luu
authors.forename: Liliya G
authors.initials: LG
authors.lastname: Nikolcheva
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Retrouvey
authors.forename: Carlos
authors.initials: C
authors.lastname: Flores-Mir
authors.forename: Tarek
authors.initials: T
authors.lastname: El-Bialy
authors.forename: Jason P
authors.initials: JP
authors.lastname: Carey
authors.forename: Paul W
authors.initials: PW
authors.lastname: Major
mesh_terms: D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D002508:Cephalometry / Q000379:methods*; D054893:Cone-Beam Computed Tomography; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D003765:Models, Dental; D009811:Odontometry / Q000379:methods*; D015203:Reproducibility of Results