title: An In Vitro Comparison of Fracture Load of Zirconia Custom Abutments with Internal Connection and Different Angulations and Thicknesses: Part II.
abstract: OBJECTIVE
  The purpose of part II of this in vitro study was to compare the fracture load of two-piece zirconia custom abutments with different thicknesses and angulations.
  
  
  METHODS
  Forty zirconia custom abutments were divided into four groups as follows: group A1: 0.7 mm thickness and 0° angulations; group A2: 0.7 mm thickness and 15° angulations; group B1: 1 mm thickness and 0° angulations; group B2: 1 mm thickness and 15° angulations. As in part I, in all groups, implant replicas were mounted in self-cure acrylic jigs to support the abutments. The zirconia custom abutments were engaged in the implant replicas using a manual torque wrench. All jigs were secured and mounted in a metallic vice and subjected to shear stress till 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 incisal edge. The test specimens used in this study did not include a crown. The universal testing machine was controlled via a computer software system, which 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 and Kolmogorov-Smirnov).
  
  
  RESULTS
  The mean fracture load of zirconia custom abutments across the groups (A1 to B2) ranged from 432 ± 97 N to 746 ± 275 N. The angulated zirconia custom abutment exhibited the highest fracture load, which was statistically significant (p = 0.045). The thickness of the zirconia custom abutment also had a positive influence on the strength of the specimens (p = 0.005).
  
  
  CONCLUSIONS
  In this study, the 15° angulated zirconia custom abutments showed the highest fracture load of those investigated. The 1 mm thick zirconia custom abutments also exhibited significantly higher fracture load compared to 0.7 mm abutments.
  
  
  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: Department of Prosthodontics and Operative Dentistry, Prosthodontics Division and Advanced Education in Esthetic Dentistry, Tufts University School of Dental Medicine, Boston, MA.
authors: Roya
authors: R
authors: Zandparsa
authors: Department of Prosthodontics and Operative Dentistry, Prosthodontics Division and Advanced Education in Esthetic Dentistry, Tufts University School of Dental Medicine, Boston, MA.
authors: Abdalah
authors: A
authors: Albosefi
mesh_terms: D017076:Computer-Aided Design; D003442:Crowns; D000044:Dental Abutments; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D008422:Materials Testing; D013314:Stress, Mechanical; D015040:Zirconium
chemical_list: D015040:Zirconium
keywords: Ceramic abutments stability; fracture load; implant/abutment connection, ceramics; shear stress; zirconia