title: Precision of intraoral digital dental impressions with iTero and extraoral digitization with the iTero and a model scanner.
abstract: BACKGROUND
  Digital impression devices are used alternatively to conventional impression techniques and materials. The aims of this study were to evaluate the precision of digital intraoral scanning under clinical conditions (iTero; Align Technologies, San Jose, Calif) and to compare it with the precision of extraoral digitization.
  
  
  METHODS
  One patient received 10 full-arch intraoral scans with the iTero and conventional impressions with a polyether impression material (Impregum Penta; 3M ESPE, Seefeld, Germany). Stone cast models manufactured from the impressions were digitized 10 times with an extraoral scanner (D250; 3Shape, Copenhagen, Denmark) and 10 times with the iTero. Virtual models provided by each method were roughly aligned, and the model edges were trimmed with cutting planes to create common borders (Rapidform XOR; Inus Technologies, Seoul, Korea). A second model alignment was then performed along the closest distances of the surfaces (Artec Studio software; Artec Group, Luxembourg, Luxembourg). To assess precision, deviations between corresponding models were compared. Repeated intraoral scanning was evaluated in group 1, repeated extraoral model scanning with the iTero was assessed in group 2, and repeated model scanning with the D250 was assessed in group 3. Deviations between models were measured and expressed as maximums, means, medians, and root mean square errors for quantitative analysis. Color-coded displays of the deviations allowed qualitative visualization of the deviations.
  
  
  RESULTS
  The greatest deviations and therefore the lowest precision were in group 1, with mean deviations of 50 μm, median deviations of 37 μm, and root mean square errors of 73 μm. Group 2 showed a higher precision, with mean deviations of 25 μm, median deviations of 18 μm, and root mean square errors of 51 μm. Scanning with the D250 had the highest precision, with mean deviations of 10 μm, median deviations of 5 μm, and root mean square errors of 20 μm. Intraoral and extraoral scanning with the iTero resulted in deviations at the facial surfaces of the anterior teeth and the buccal molar surfaces.
  
  
  CONCLUSIONS
  Scanning with the iTero is less accurate than scanning with the D250. Intraoral scanning with the iTero is less accurate than model scanning with the iTero, suggesting that the intraoral conditions (saliva, limited spacing) contribute to the inaccuracy of a scan. For treatment planning and manufacturing of tooth-supported appliances, virtual models created with the iTero can be used. An extended scanning protocol could improve the scanning results in some regions.
authors.affiliation: Division of Oral and Maxillofacial Surgery, University Medical Center, Freiburg, Germany. tabea.viktoria.fluegge@uniklinik-freiburg.de
authors.forename: Tabea V
authors.initials: TV
authors.lastname: Flügge
authors.forename: Stefan
authors.initials: S
authors.lastname: Schlager
authors.forename: Katja
authors.initials: K
authors.lastname: Nelson
authors.forename: Susanne
authors.initials: S
authors.lastname: Nahles
authors.forename: Marc C
authors.initials: MC
authors.lastname: Metzger
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D003760:Dental Impression Materials; D003761:Dental Impression Technique / Q000295:instrumentation; D061827:Dimensional Measurement Accuracy; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation; D003765:Models, Dental; D016382:Orthodontic Appliance Design / Q000379:methods; D018709:Statistics, Nonparametric; D015898:Tomography Scanners, X-Ray Computed
chemical_list: D003760:Dental Impression Materials