title: Comparative evaluation of impression accuracy of tilted and straight implants in All-on-Four technique.
abstract: OBJECTIVE
  The aim of this in vitro study was to compare the accuracy of implant impressions in parallel and nonparallel implants of All-on-Four treatment plan.
  
  
  METHODS
  A reference model containing 4 internal-connection implant analogs was fabricated according to All-on-Four treatment plan (2 anterior implants at 0 degree and 2 posterior implants at 30 degrees in relation to the perpendicular line). Twenty impressions of this model were made using open-tray impression technique. Impressions were poured with American Dental Association type 4 stone, and the positional accuracy of the implant replica heads in x-, y-, and z- axes was evaluated using a coordinate measuring machine. These measurements were compared with the obtained measurements from the reference model that served as control, and data were analyzed using independent test (α = 0.05).
  
  
  RESULTS
  The results showed that the accuracy of the implant impressions did not show any significant difference between the tilted and straight implants except in y-coordinate (P = 0.012).
  
  
  CONCLUSIONS
  Within the limitations of this study, the accuracy of the implant impressions did not differ for different implant angulations in All-on-Four treatment plan.
authors.affiliation: *Dentist, Dental Students' Research Center, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. †Associate Professor, Implant Research Center and Department of Prosthodontics and Implant, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. ‡Associate Professor, Dental Research Center and Department of Prosthodontics and Implant, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Sara
authors.initials: S
authors.lastname: Ehsani
authors.forename: Hakimeh
authors.initials: H
authors.lastname: Siadat
authors.forename: Marzieh
authors.initials: M
authors.lastname: Alikhasi
mesh_terms: D003760:Dental Impression Materials; D003761:Dental Impression Technique / Q000592:standards; D019094:Dental Prosthesis, Implant-Supported / Q000379:methods* / Q000592:standards; D006801:Humans; D066298:In Vitro Techniques
chemical_list: D003760:Dental Impression Materials