title: Laser digitization of casts to determine the effect of tray selection and cast formation technique on accuracy.
abstract: STATEMENT OF PROBLEM; Several studies have attempted to determine the ideal combination of dental materials and laboratory techniques to produce the most accurate dental cast. Most have made use of 2-dimensional manual measuring devices, which neglect to account for the dimensional changes that exist along a 3-dimensional surface.
  
  
  OBJECTIVE
  The purpose of this study was to determine the effect of impression tray selection and cast formation techniques on the dimensional change of a dental cast with the use of new, 3-dimensional optical digitizing technology.
  
  
  METHODS
  Multiple impressions of a machined steel die that resembled a dental arch were made with custom and stock impression trays and vinyl polysiloxane impression material. The impressions were poured in type V artificial dental stone and allowed to set with the tray inverted or noninverted. The steel master die and stone casts were digitized with the Steinbichler Comet 100 Optical Digitizer, which was developed at the Minnesota Dental Research Center for Biomaterials and Biomechanics. Three-dimensional images of the stone casts were aligned to the 3-dimensional image of the master die and analyzed with AnSur-NT software. Multiple measurements of the master die and stone casts were analyzed to determine the accuracy of the 3-dimensional technology and of the impression and cast fabrication techniques. Planar distances between the center of each crown preparation were measured, as were crown heights. Data were analyzed with analysis of variance (P<.05), and root mean square error values were determined.
  
  
  RESULTS
  Casts were compared with a total of 45 significance tests, of which only 4 yielded P<.05. There was no pattern to these results, which suggests that they were false-positive findings.
  
  
  CONCLUSIONS
  Results obtained with the use of new optical digitizing technology indicated that neither impression tray type nor cast formation technique affected the accuracy of final casts.
authors.affiliation: Division of Prosthodontics, Department of Restorative Sciences, School of Dentistry, University of Minnesota, Minneapolis 55455, USA. brosk001@umn.edu
authors.forename: Mary E
authors.initials: ME
authors.lastname: Brosky
authors.forename: Igor J
authors.initials: IJ
authors.lastname: Pesun
authors.forename: Philip D
authors.initials: PD
authors.lastname: Lowder
authors.forename: Ralph
authors.initials: R
authors.lastname: Delong
authors.forename: James S
authors.initials: JS
authors.lastname: Hodges
mesh_terms: D000704:Analysis of Variance; D003760:Dental Impression Materials; D003761:Dental Impression Technique / Q000295:instrumentation*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007834:Lasers; D003765:Models, Dental; D011145:Polyvinyls; D015203:Reproducibility of Results; D012833:Siloxanes; D012984:Software; D018709:Statistics, Nonparametric
chemical_list: D003760:Dental Impression Materials; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane