title: Multibracket appliance: impression defaults and their reduction by blocking-out  -  a three-dimensional study.
abstract: OBJECTIVE
  This study examines accuracy of dental impressions and following plaster models taken during treatment with fixed appliances.
  
  
  METHODS
  A maxillary typodont was provided with brackets. Three examiners took impressions three times each of the variants: brackets only, archwire fixed by alastics, ligatures or Kobayashi-hooks, and brackets and archwire covered completely or just on the gingival side by protection or impression wax. Casts were scanned using Activity102(®). Virtual models were compared to the scan of the typodont using Comparison(®). Differences were measured and descriptively analyzed. Estimated means with 95% confidence intervals were computed. Significance was assessed using linear mixed models.
  
  
  RESULTS
  While pyramidal reference blocks had a mean difference of 0.019 mm (95% CI = 0.017-0.021 mm) to the master model, teeth without attachments showed 0.097 mm (95% CI = 0.082-0.111 mm), and teeth with brackets 0.169 mm (95% CI = 0.156-0.182 mm) (p < 0.001). Smallest mean was found when using protection wax only on the gingival bracket side (0.152 mm (95% CI = 0.113-0.192 mm)). Incisors deviated most (0.258 mm (95 % CI = 0.239-0.277 mm)).
  
  
  CONCLUSIONS
  Teeth with brackets make impressions more inaccurate because of undercuts. Removing the archwire before taking the impression or covering the brackets on the gingival side shows tendencies toward better precision.
  
  
  CONCLUSIONS
  Taking impressions during treatment with fixed appliances, some inaccuracy has to be taken into account.
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Johannes Gutenberg-University Mainz Medical Center, Augustusplatz 2, Mainz, 55131, Germany. susanne.wriedt@unimedizin-mainz.de.
authors.forename: Susanne
authors.initials: S
authors.lastname: Wriedt
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Johannes Gutenberg-University Mainz Medical Center, Augustusplatz 2, Mainz, 55131, Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Foersch
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Johannes Gutenberg-University Mainz Medical Center, Augustusplatz 2, Mainz, 55131, Germany.
authors.forename: Jan Daniel
authors.initials: JD
authors.lastname: Muhle
authors.affiliation: Institute of Medical Biostatistics, Epidemiology, Informatics, Johannes Gutenberg-University Mainz Medical Center, Obere Zahlbacher Strasse 69, Mainz, 55131, Germany.
authors.forename: Irene
authors.initials: I
authors.lastname: Schmidtmann
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Johannes Gutenberg-University Mainz Medical Center, Augustusplatz 2, Mainz, 55131, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Wehrbein
mesh_terms: D017076:Computer-Aided Design; D003760:Dental Impression Materials; D003761:Dental Impression Technique; D061827:Dimensional Measurement Accuracy; D005858:Germany; D006801:Humans; D003765:Models, Dental; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D012984:Software
chemical_list: D003760:Dental Impression Materials
keywords: 3D scanner; Accuracy; Alginate; Dental impression; Digital model; Orthodontic brackets