title: Accuracy of implant impressions without impression copings: a three-dimensional analysis.
abstract: BACKGROUND
  Implant impressions without impression copings can be used for cement-retained implant restorations. A comparison of the accuracy of implant impressions with and without impression copings is needed.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate and compare the dimensional accuracy of implant definitive casts that are fabricated by implant impressions with and without impression copings.
  
  
  METHODS
  An acrylic resin maxillary model was fabricated, and 3 implant replicas were secured in the right second premolar, first, and second molars. Two impression techniques were used to fabricate definitive casts (n=10). For the coping group (Group C), open tray impression copings were used for the final impressions. For the no-coping group (Group NC), cementable abutments were connected to the implant replicas, and final impressions were made assuming the abutments were prepared teeth. Computerized calculation of the centroids and long axes of the implant or stone abutment replicas was performed. The Mann-Whitney U test analyzed the amount of linear and rotational distortion between groups (α =.05).
  
  
  RESULTS
  At the first molar site, Group NC showed significantly greater linear distortion along the Y-axis, with a small difference between the groups (Group C, 7.8 ± 7.4 μm; Group NC, 19.5 ± 12.2). At the second molar site, increased distortion was noted in Group NC for every linear and rotational variable, except for linear distortion along the Z-axis.
  
  
  CONCLUSIONS
  Implant impression with open tray impression copings produced more accurate definitive casts than those fabricated without impression copings, especially those with greater inter-abutment distance.
authors.affiliation: Department of Prosthodontics, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University, Seoul, Korea.
authors.forename: Joo-Hyun
authors.initials: JH
authors.lastname: Kwon
authors.forename: Yong-Ha
authors.initials: YH
authors.lastname: Son
authors.forename: Chong-Hyun
authors.initials: CH
authors.lastname: Han
authors.forename: Sunjai
authors.initials: S
authors.lastname: Kim
mesh_terms: D002484:Cementation; D003761:Dental Impression Technique / Q000295:instrumentation*; D017268:Dental Prosthesis Retention / Q000379:methods; D019094:Dental Prosthesis, Implant-Supported; D021621:Imaging, Three-Dimensional; D008437:Maxilla; D003765:Models, Dental