title: Comparison of Different Impression Techniques When Using the All-on-Four Implant Treatment Protocol.
abstract: OBJECTIVE
  The aim of this in vitro study was to compare the accuracy of two different impression techniques for the All-on-Four implant therapy protocol.
  
  
  METHODS
  An acrylic resin analog for an edentulous maxilla with four internal connection implants (Replace Select, Nobel Biocare) was fabricated according to the All-on-Four protocol. A total of 40 impressions were made with different techniques (open and closed tray) at abutment and implant levels and poured in type IV dental stone. A coordinate measuring machine was used to record the x, y, and z coordinates and angular displacement. The measurements were compared with those obtained from the reference model. Data were analyzed with analysis of variance and t test at α = .05.
  
  
  RESULTS
  There was less linear and rotational displacement for the open-tray technique when compared with the closed-tray technique (P = .02 and P < .001, respectively). Impressions made at abutment level produced fewer linear and rotational displacements when compared with implant level impressions using the open-tray technique for straight and angulated implants (P = .04 and P < .001, respectively). However, less rotational dislocation was observed for impressions made with the closed-tray technique when compared with the open-tray technique at implant level (P < .001).
  
  
  CONCLUSIONS
  Choice of impression technique affected the accuracy of impressions, and less displacement was observed with the open-tray method. Abutment-level impressions with an open-tray technique were more accurate, while implant-level impressions were more accurate when a closed-tray technique was used.
authors.forename: Hakimeh
authors.initials: H
authors.lastname: Siadat
authors.forename: Marzieh
authors.initials: M
authors.lastname: Alikhasi
authors.forename: Elaheh
authors.initials: E
authors.lastname: Beyabanaki
authors.forename: Susan
authors.initials: S
authors.lastname: Rahimian
mesh_terms: D000044:Dental Abutments; D015921:Dental Implants; D003761:Dental Impression Technique / Q000295:instrumentation / Q000592:standards*; D006801:Humans; D007575:Jaw, Edentulous / Q000473:pathology; D008422:Materials Testing; D008437:Maxilla / Q000473:pathology; D008953:Models, Anatomic; D012399:Rotation; D013499:Surface Properties
chemical_list: D015921:Dental Implants