title: Influence of implant angulation on the fracture resistance of zirconia abutments.
abstract: OBJECTIVE
  To investigate the effects of abutment design to correct for implant angulation and aging on the fracture resistance of zirconia abutments. Greater understanding of the fracture strength of the zirconia abutments under various clinical conditions may lead to improvement of clinical protocols and possibly limit potential failures of implant prosthetics.
  
  
  METHODS
  Test specimens consisted of an implant-zirconia abutment-zirconia crown assembly with implant apex positioned at 0°, 20° to the facial (20F), and 20° to the lingual (20L) with respect to a constant crown contour. To keep the abutment design as the only variable, CAD/CAM technology was used to generate monolithic zirconia crowns identical both in external and internal dimensions and marginal contours to precisely fit all the abutments in an identical fashion. The monolithic zirconia abutments were designed to fit the constant crown contours and the internal connection of the implant at the three angulations. The customized abutments for the three implant angulations varied in emergence profile, screw hole location, and material thickness around the screw hole. Half the specimens from each group were subjected to steam autoclaving and thermocycling to simulate aging of the restorations in vivo. To mimic the off-axis loading of the central incisor, the specimens were loaded at the recommended cephalometric interincisal relationship of 135° between the long axis of the crown supported by the implant and the Instron force applicator simulating the mandibular incisor. The force applicator was positioned 2 mm from the incisal edge and loaded at a 1 mm/min crosshead speed. Data were evaluated by 2-way ANOVA (α = 0.05) and Tukey's HSD.
  
  
  RESULTS
  The 20F group had the highest fracture values followed by the 0° group, and the 20L group had the lowest fracture values. Aging did not yield any significant difference in fracture force magnitudes.
  
  
  CONCLUSIONS
  Within the limitations of this study, tilting the implant apex to the lingual significantly reduced the fracture strength of angle-corrected zirconia abutments. Accordingly, while the angle between the occlusal force application and the long axis of the implant decreases, the resistance (force) to fracture decreases.
authors: Graduate Prosthodontics Resident, Department of Restorative Sciences, School of Dentistry, University of Alabama, Birmingham, AL.
authors: Shreedevi
authors: S
authors: Thulasidas
authors: Daniel A
authors: DA
authors: Givan
authors: Jack E
authors: JE
authors: Lemons
authors: Sandra Jean
authors: SJ
authors: O'Neal
authors: Lance C
authors: LC
authors: Ramp
authors: Perng-Ru
authors: PR
authors: Liu
mesh_terms: D000704:Analysis of Variance; D017076:Computer-Aided Design; D003442:Crowns; D000044:Dental Abutments; D059605:Dental Implant-Abutment Design; D008422:Materials Testing; D013314:Stress, Mechanical; D015040:Zirconium / Q000737:chemistry*
chemical_list: D015040:Zirconium; C028541:zirconium oxide
keywords: Custom zirconia abutment; aging; angled implant; angled zirconia abutment; fracture strength; shorter internal connection