Monotonic and Fatigue Strength of 3D-Printed Partially Stabilized Zirconia for Monolithic Restorations

To investigate the monotonic and fatigue strength of 3D-printed 5 mol% yttria partially stabilized zirconia (5Y-PSZ) and the influences of printing layer orientation and finishing protocol. Bar-shaped 5Y-PSZ specimens (1.0 mm x 1.0 mm x 12.0 mm) were 3D-printed via stereolithography, followed by debinding and sintering. The specimens were randomly divided into 2 groups according to printing layer orientations: parallel or perpendicular to the tensile surface of a 3-point bending test. The specimens of each printing layer orientation were subsequently submitted to different surface finishing protocols: as-sintered, polished, and glazed. The monotonic strength of each group was determined using a ball-in-hole device. A step-wise fatigue test was conducted for the polished and glazed specimens. For monotonic strength, the parallel specimens (640 ± 99 MPa) were stronger than the perpendicular (507 ± 48 MPa); polishing generated higher strength for both parallel (782 ± 134 MPa) and perpendicular (645 ± 160 MPa) orientations; while the effect of glazing was not significant, the glazed perpendicular specimen (623 ± 97 MPa) presented similar strength to the glazed parallel specimens (581 ± 117 MPa). However, the fatigue strength was similar in the evaluated groups (parallel and polished: 418 ± 115 MPa; perpendicular and polished: 404 ± 55 MPa; parallel and glazed: 406 ± 41 MPa; perpendicular and glazed: 371 ± 86 MPa). Both printing layer orientation and surface finishing influenced the monotonic strength of 3D-printed 5Y-PSZ, while fatigue strength did not differ significantly among polished and glazed specimens with different orientations.