title: On the augmented reproducibility in measurements on 3D orthodontic digital dental models and the definition of feature points.
abstract: OBJECTIVE
  The objective of this study was to explore digital measurement methodology on 3-dimensional (3D) dental models. Standardised manipulation and practices have lead to reliable measurements on plaster casts. Identifying landmarks on digital models or digitised plaster casts is fundamentally different from actual measurements. Three-dimensional models are represented on flat screens and landmarks are individually indentified. A procedure is proposed that resolves the deficiencies associated with a 2-dimensional (2D) display through an appropriate model representation and through local optimisation.
  
  
  METHODS
  Fifteen models (OrthoProof) were exported to a locally developed 3D point indication software package, in which two measurement approaches were implemented involving standard projection with and without local search. Nine linear measurements were obtained from plaster casts and digital models. Statistical analysis included correlation and Friedman s nonparametric analysis of variance (ANOVA).
  
  
  RESULTS
  For five out of nine linear measurements, digital indications yielded results significantly different from manual measurements (p = 0.05). Local search considerably improved measurement accuracy and reliability.
  
  
  CONCLUSIONS
  Measurements on plaster casts can differ significantly from those obtained through digital identification methods. These differences prove to be clinically relevant. Standardisation and optimisation resulted in improved and extremely reliable digital measurements.
authors.affiliation: Vrije Universiteit Brussel, Department of Orthodontics - SOPA, Laarbeeklaan 103, 1090 Jette, Belgium. wjacquet@vub.ac.be
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Jacquet
authors.forename: Edgard
authors.initials: E
authors.lastname: Nyssen
authors.forename: Gabriele
authors.initials: G
authors.lastname: Ibel
authors.forename: Bart Vande
authors.initials: BV
authors.lastname: Vannet
mesh_terms: D059925:Anatomic Landmarks / Q000033:anatomy & histology; D001641:Bicuspid / Q000033:anatomy & histology; D003196:Computer Graphics; D003481:Cuspid / Q000033:anatomy & histology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008029:Lighting; D003765:Models, Dental; D008963:Molar / Q000033:anatomy & histology; D009811:Odontometry / Q000379:methods*; D015203:Reproducibility of Results; D012984:Software; D019228:Tooth Crown / Q000033:anatomy & histology; D014584:User-Computer Interface