title: Can the intra-examiner variability of Little's Irregularity Index be improved using 3D digital models of study casts?
abstract: OBJECTIVE
  To compare contact point displacement measurements, used to determine the Little's Irregularity Index (LII) score on study casts and digital models of study casts by an independent examiner.
  
  
  METHODS
  The contact point displacement measurements of the six maxillary anterior labial teeth were measured on ten study casts using digital callipers and their associated digital models using Creo Parametric software on five occasions following scanning using a LAVA Chairside Oral Scanner (LCOS) three-dimensional (3D) intra oral scanner. Means, standard deviations and coefficients of variation (CoV) were determined, data analyses (Pearson's correlation coefficients (PCCs) and Intraclass correlation coefficients (ICCs)) and statistical analyses (three and two-way analyses of variance (ANOVAs) and Independent Sample Student's t-tests) were carried out (p<0.05).
  
  
  RESULTS
  Significant positive correlations for the contact point displacement measurements were evident between all measurement time points for the study casts (r>0.978; p<0.0001 and ICC>0.910; p<0.0001) and the digital models (r>0.963; p<0.0001 and ICC>0.986; p<0.0001). The CoV results showed that the contact point displacement measurement data from the digital models was more reproducible than the study casts. Of the 50 Independent Sample Student's t-tests, 21 significant increases (p<0.042) were reported in contact point displacement measurements <2.9 mm for the digital models compared with the study casts.
  
  
  CONCLUSIONS
  The use of 3D digital models can improve the reliability of LII measurements by reducing the subjectivity associated with choosing the anatomic tooth contact points and the awkwardness of measuring the contact point displacements on study casts using a cumbersome calliper technique.
  
  
  CONCLUSIONS
  Intra-examiner variability in the measurement of LII is still evident with digital models suggesting that either improved software specifically aimed at the orthodontic community be identified or a new method for measuring anterior incisor crowding be sought.
authors.affiliation: Materials Science Unit, Dublin Dental University Hospital, Trinity College Dublin, Lincoln Place, Dublin 2, Ireland.
authors.forename: Adam H
authors.initials: AH
authors.lastname: Dowling
authors.forename: Angus
authors.initials: A
authors.lastname: Burns
authors.forename: Donal
authors.initials: D
authors.lastname: Macauley
authors.forename: Thérèse M
authors.initials: TM
authors.lastname: Garvey
authors.forename: Garry J P
authors.initials: GJ
authors.lastname: Fleming
mesh_terms: D000293:Adolescent; D003481:Cuspid / Q000473:pathology; D003735:Dental Casting Technique; D003761:Dental Impression Technique; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000706:statistics & numerical data*; D021621:Imaging, Three-Dimensional / Q000706:statistics & numerical data*; D007180:Incisor / Q000473:pathology; D008310:Malocclusion / Q000145:classification* / Q000473:pathology; D003765:Models, Dental / Q000706:statistics & numerical data*; D015588:Observer Variation; D009811:Odontometry / Q000295:instrumentation / Q000379:methods; D010781:Photography / Q000295:instrumentation; D011446:Prospective Studies; D015203:Reproducibility of Results
keywords: 3D intra-oral scanner; Digital models; Intra-examiner variability; Little's irregularity index; Orthodontics; Study casts