title: The Effect of Implant Angulation on the Transfer Accuracy of External-Connection Implants.
abstract: BACKGROUND
  Accurate recording of implant location is required in every implant-supported prostheses. Implant angulation, which is inevitable in various clinical situations, could affect the impression accuracy.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to compare the transfer accuracy of straight and tilted implants of All-on-4 protocol with implant or abutment level impression making and different techniques of direct and indirect.
  
  
  METHODS
  One reference model of edentulous maxilla with four external connection implants (Brånemark) inserted according to All-on-4 protocol was made. Forty impressions of this model were made at implant (groups 1 and 2) or abutment (groups 3 and 4) levels with different techniques of direct or indirect, respectively. Impressions were poured with type IV dental stone. Coordinate measuring machine was used to record x, y, and z coordinates and also angular dislocation of implants. These measurements were compared with the equals calculated on the reference model. Data were analyzed with univariate analysis of variance and t-test at α = 0.05.
  
  
  RESULTS
  The results showed that abutment level impression making (groups 3 and 4), either with direct or indirect technique, produced the same results for straight and tilted implants of Δr variable (p > .05), though in implant level groups (groups 1 and 2), it was statistically significant (p < .05). However, only implant level impression making with direct technique (group 1) had the same results of angular accuracy for straight and tilted implants.
  
  
  CONCLUSIONS
  Impression technique (direct or indirect) had significant effect on the impression accuracy of tilted implants, and direct technique produced less inaccuracy. Also, abutment level impressions showed more accuracy than implant level impressions.
authors.affiliation: Dental Research Center and Department of Prosthodontics, Tehran University of Medical Sciences School of Dentistry, Tehran, Iran.
authors.forename: Marzieh
authors.initials: M
authors.lastname: Alikhasi
authors.affiliation: Dental Implant Research Center and Department of Prosthodontics, Tehran University of Medical Sciences School of Dentistry, Tehran, Iran.
authors.forename: Hakimeh
authors.initials: H
authors.lastname: Siadat
authors.affiliation: Dental Implant Research Center and Department of Oral and Maxillofacial Radiology, Tehran University of Medical Sciences School of Dentistry, Tehran, Iran.
authors.forename: Susan
authors.initials: S
authors.lastname: Rahimian
mesh_terms: D000044:Dental Abutments; D015921:Dental Implants; D003764:Dental Materials / Q000627:therapeutic use*; D019094:Dental Prosthesis, Implant-Supported / Q000379:methods*; D003799:Dental Stress Analysis; D006801:Humans
chemical_list: D015921:Dental Implants; D003764:Dental Materials
keywords: abutment; angled abutment; implant; impression; tilted implant