title: Dimensional accuracy of jaw scans performed on alginate impressions or stone models: A practice-oriented study.
abstract: OBJECTIVE
  Digital jaw models offer more extensive possibilities for analysis than casts and make it easier to share and archive relevant information. The aim of this study was to compare the dimensional accuracy of scans performed on alginate impressions and on stone models to reference scans performed on underlying resin models.
  
  
  METHODS
  Precision spheres 5 mm in diameter were occlusally fitted to the sites of the first premolars and first molars on a pair of jaw models fabricated from resin. A structured-light scanner was used for digitization. Once the two reference models had been scanned, alginate impressions were taken and scanned after no later than 1 h. A third series of scans was performed on type III stone models derived from the impressions. All scans were analyzed by performing five repeated measurements to determine the distances between the various sphere centers.
  
  
  RESULTS
  Compared to the reference scans, the stone-model scans were larger by a mean of 73.6 µm (maxilla) or 65.2 µm (mandible). The impression scans were only larger by 7.7 µm (maxilla) or smaller by 0.7 µm (mandible). Median standard deviations over the five repeated measurements of 1.0 µm for the reference scans, 2.35 µm for the impression scans, and 2.0 µm for the stone-model scans indicate that the values measured in this study were adequately reproducible.
  
  
  CONCLUSIONS
  Alginate impressions can be suitably digitized by structured-light scanning and offer considerably better dimensional accuracy than stone models. Apparently, however, both impression scans and stone-model scans can offer adequate precision for orthodontic purposes. The main issue of impression scans (which is incomplete representation of model surfaces) is being systematically explored in a follow-up study.
authors.affiliation: Department of Orthodontics and Orofacial Orthopedics, Center for Dental, Oral and Maxillary Medicine, University of Ulm Medical School, Ulm, Germany, annike.vogel@uniklinik-ulm.de.
authors.forename: Annike B
authors.initials: AB
authors.lastname: Vogel
authors.forename: Fatih
authors.initials: F
authors.lastname: Kilic
authors.forename: Falko
authors.initials: F
authors.lastname: Schmidt
authors.forename: Sebastian
authors.initials: S
authors.lastname: Rübel
authors.forename: Bernd G
authors.initials: BG
authors.lastname: Lapatki
mesh_terms: D000464:Alginates; D000886:Anthropometry / Q000379:methods*; D003760:Dental Impression Materials; D003761:Dental Impression Technique; D020723:Glucuronic Acid; D006603:Hexuronic Acids; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007568:Jaw / Q000033:anatomy & histology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D000464:Alginates; D003760:Dental Impression Materials; D006603:Hexuronic Acids; D020723:Glucuronic Acid