title: An in vitro comparison of fracture load of zirconia custom abutments with internal connection and different angulations and thickness: part I.
abstract: OBJECTIVE
  The purpose of this in vitro study was to compare the fracture load of one-piece zirconia custom abutments with different thicknesses and angulations.
  
  
  METHODS
  Forty zirconia custom abutments were divided into four groups. Group A-1 and group B-1 simulated a clinical situation with an ideal implant position, which allows for the use of straight zirconia custom abutments with two thicknesses (0.7 and 1 mm). Groups A-2 and B-2 simulated a situation with a compromised implant position requiring 15° angulated abutments with different thicknesses (0.7 and 1 mm). Implant replicas were mounted in self-cure acrylic jigs to support the abutments in all groups. The zirconia custom abutments were engaged in the implant replicas using a manual torque wrench. Each jig was secured and mounted in a metallic vice 30° relative to a mechanical indenter. All groups were subjected to shear stress until failure using a universal testing machine with a 0.5 mm/min crosshead speed with the force transferred to the lingual surface of the zirconia custom abutments 2 mm below the top surface. The universal testing machine was controlled via a computer software system that also completed the stress-strain diagram and recorded the breaking fracture load. The fracture loads were recorded for comparison among the groups and subjected to statistical analysis (two-way ANOVA).
  
  
  RESULTS
  The mean fracture load of zirconia custom abutments across the groups (A-1 through B-2) ranged from 160 ± 60 to 230 ± 95 N. The straight zirconia custom abutment exhibited the highest fracture load among the groups (p = 0.009); however, the thickness of the zirconia custom abutment had no influence on the strength of any of the specimens (p = 0.827).
  
  
  CONCLUSIONS
  There was no statistically significant difference in fracture strength between the 0.7 and 1.0 mm groups; however, angulated zirconia custom abutments had the lowest fracture load.
  
  
  CONCLUSIONS
  The results of this in vitro study will help dental practitioners with their decision-making process in selecting the type of custom abutment to be used clinically.
authors.affiliation: Former resident, Prosthodontic Division and Advanced Education in Esthetic Dentistry, Department of Prosthodontics and Operative Dentistry, Tufts University School of Dental Medicine, Boston, MA.
authors.forename: Abdalah
authors.initials: A
authors.lastname: Albosefi
authors.forename: Matthew
authors.initials: M
authors.lastname: Finkelman
authors.forename: Roya
authors.initials: R
authors.lastname: Zandparsa
mesh_terms: D002516:Ceramics / Q000737:chemistry; D017076:Computer-Aided Design; D000044:Dental Abutments; D059605:Dental Implant-Abutment Design; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D019415:Torque; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide
keywords: Ceramic abutment stability; ceramics; implant/abutment connection; shear stress