An in Vitro Comparison of Fracture Load of Zirconia Custom Abutments with Internal Connection and Different Angulations and Thickness: Part I

Purpose: The purpose of this in vitro study was to compare the fracture load of one-piece zirconia custom abutments with different thicknesses and angulations. Materials and 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. Clinical Implication: 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.