Effect of different implant-abutment connection materials on the fracture resistance of zirconia abutments

The aim of the present in vitro study was to assess the modes of failures under static load among titanium (Ti) and 1- and 2-piece zirconia abutments. The 1- and 2-piece zirconia abutment specimens were fabricated from prescanned Ti abutments. Twenty-one implant abutments and 21 implant replicas were equally divided into 3 groups as follows: (a) Group 1 (Titanium group); (b) Group 2 (1-piece zirconia abutment group); and (c) Group 3: 2-piece zirconia abutment group). A 250 000-cycle linear fatigue load ranging between 10 N and 210 N was applied to all specimens using an all-electric dynamic test instrument. The specimens were loaded until they fractured. In all groups, assessment of mode of fracture was done on visual assessment by a trained and calibrated investigator. Prior sample-size estimation was performed; and sample distribution was assessed using the Kolmogorov and Shapiro tests. Screw fracture (n ¼ 7) and abutment bending at the apical part (n ¼ 7) occurred in the Ti group. In the 1-piece zirconia group, screw and abutment fractures occurred in 7 and 7 cases, respectively. In the 2-piece zirconia screw fracture (n ¼ 7) above the Ti zirconia junction (transgingival segment) and abutment fracture (n ¼ 7) were determined as the failure modes. In vitro, the 1-piece zirconia abutments are more fracture resistant than titanium and 2-piece zirconia abutments. From a clinical perspective, further studies are needed to determine the minimum static load value required to induce fracture of the 1- and 2-piece zirconia abutments.