title: A comparison of precision of fit, rotational freedom, and torque loss with copy-milled zirconia and prefabricated titanium abutments.
abstract: OBJECTIVE
  The present study sought to compare copy-milled zirconia abutments with standard prefabricated titanium abutments in terms of horizontal and vertical misfit, rotational freedom, and torque loss.
  
  
  METHODS
  Twenty regular-platform implants (Brånemark, Nobel Biocare) with a standard external-hexagon implant-abutment interface were divided into two groups. In one group, prefabricated titanium abutments (Easy Abutment, Nobel Biocare) were used; in the other group, custom-made zirconia abutments were fabricated using the Zirkonzahn milling system. Measurements of geometry, rotational freedom, and marginal discrepancy were performed using a video measuring machine. To measure torque loss, each abutment was torqued to 32 Ncm and then loosened with a digital torque wrench. The torque loss values were reported as a percentage of the applied torque.
  
  
  RESULTS
  Rotational freedom and horizontal misfit were significantly higher with the customized abutments. There were no statistically significant differences in vertical misfit or in mean percentage of torque loss between the two groups.
  
  
  CONCLUSIONS
  Within the limitations of this study, it could be concluded that copy-milled zirconia abutments do not fit as accurately as prefabricated titanium abutments. However, the less precise fit of customized zirconia abutments does not seem to affect their ability to maintain the applied torque.
authors.affiliation: Dental Research Center and Department of Prosthodontics and Implants, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Marzieh
authors.initials: M
authors.lastname: Alikhasi
authors.forename: Abbas
authors.initials: A
authors.lastname: Monzavi
authors.forename: Seyed Hossein
authors.initials: SH
authors.lastname: Bassir
authors.forename: Roshanak Baghai
authors.initials: RB
authors.lastname: Naini
authors.forename: Nasim
authors.initials: N
authors.lastname: Khosronedjad
authors.forename: Sareh
authors.initials: S
authors.lastname: Keshavarz
mesh_terms: D001672:Biocompatible Materials; D000044:Dental Abutments / Q000592:standards*; D015921:Dental Implants / Q000592:standards*; D018772:Dental Marginal Adaptation; D055595:Mechanical Phenomena; D011897:Random Allocation; D012399:Rotation; D014025:Titanium; D019415:Torque; D015040:Zirconium
chemical_list: D001672:Biocompatible Materials; D015921:Dental Implants; D015040:Zirconium; D014025:Titanium; C028541:zirconium oxide