title: Accuracy of impression scanning compared with stone casts of implant impressions.
abstract: BACKGROUND
  Accurate virtual implant models are a necessity for the fabrication of precisely fitting superstructures.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate different methods with which to build an accurate virtual model of a 3-dimensional implant in the oral cavity; this model would then be used for iterative computer-aided design and computer-aided manufacturing (CAD-CAM) procedures.
  
  
  METHODS
  A titanium master model with 3 rigidly connected implants was manufactured and digitized with a noncontact industrial scanner to obtain a virtual master model. Impressions of the master model with the implant position locators (IPL) were made using vinyl siloxanether material. The impressions were scanned (Impression scanning technique group). For the transfer technique and pick-up technique groups (each group n=20), implant analogs were inserted into the impression copings, impressions were made using polyether, and casts were poured in Type 4 gypsum. The IPLs were screwed into the analogs and scanned. To compare the virtual master model with each virtual test model, a CAD interactive software, ATOS professional, was applied. The Kruskal-Wallis test was subsequently used to determine the overall difference between groups, with the Mann-Whitney U test used for pairwise comparisons. Through Bonferroni correction, the α-level was set to .017.
  
  
  RESULTS
  The outcome revealed a significant difference among the 3 groups (P<.01) in terms of accuracy. With regard to total deviation, for all axes, the transfer technique generated the greatest divergence, 0.078 mm (±0.022), compared with the master model. Deviation with the pick-up technique was 0.041 mm (±0.009), with impression scanning generating the most accurate models with a deviation of 0.022 mm (±0.007).
  
  
  CONCLUSIONS
  The impression scanning method improved the precision of CAD-CAM-fabricated superstructures.
authors.affiliation: Assistant Professor, University Clinic Erlangen, Dental Clinic 2, Department of Prosthodontics, Glueckstrasse, Erlangen, Germany. Electronic address: ragai.matta@uk-erlangen.de.
authors.forename: Ragai Edward
authors.initials: RE
authors.lastname: Matta
authors.affiliation: Assistant Professor, Department of Medical Informatics, Biometry and Epidemiology, Universitaetsstrasse, Erlangen, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Adler
authors.affiliation: Professor, University Clinic Erlangen, Dental Clinic 2, Department of Prosthodontics, Glueckstrasse, Erlangen, Germany.
authors.forename: Manfred
authors.initials: M
authors.lastname: Wichmann
authors.affiliation: Professor, University Clinic Erlangen, Dental Clinic 2, Department of Prosthodontics, Glueckstrasse, Erlangen, Germany.
authors.forename: Siegfried Martin
authors.initials: SM
authors.lastname: Heckmann
mesh_terms: D017076:Computer-Aided Design; D015921:Dental Implants; D003761:Dental Impression Technique; D017267:Dental Prosthesis Design / Q000379:methods*; D019094:Dental Prosthesis, Implant-Supported / Q000379:methods; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D066298:In Vitro Techniques; D015203:Reproducibility of Results
chemical_list: D015921:Dental Implants