Effect of printing layer orientation and finishing protocol on the fracture behavior of 5Y-PSZ ceramic by 3D printing

Introduction: 3D printing has emerged as a promising technique for fabricating permanent dental ceramic restorations. However, there is limited literature regarding aesthetic ceramics for monolithic restorations, such as 5 mol% yttria partially stabilized zirconia (5Y-PSZ). Therefore, the aim of this study was to investigate the influence of printing layer orientation and finishing protocol on the fracture behavior of 5Y-PSZ by stereolithography (SLA) 3D printing.

Materials and Methods: Bar-shaped 5Y-PSZ specimens were 3D-printed via SLA, followed by debinding and sintering. The dimension of the as-sintered specimens was 1.0 mm x 1.0 mm x 12.0 mm. The specimens were randomly divided into two groups according to printing layer orientations: parallel or perpendicular to the tensile surface in the following bending test. The specimens of each printing layer orientation were subsequently submitted to different surface finishing protocols: as-sintered, polished, and glazed. The fracture strength of each group was determined using a ball-in-hole device. The fractured specimens were examined under a scanning electron microscope to identify the fracture origin.

Results: Two-way analyses of variance showed significant effects of printing layer orientation (p<0.001) and finishing protocol (p<0.001), while the interaction of factors was not significant (p=0.195). The parallel orientation (639.9 ± 98.6 MPa) was stronger than the perpendicular (506.9 ± 47.9 MPa) for the as-sintered specimens. Polishing significantly improved the strength for both parallel (782.0 ± 134.0 MPa)^A and perpendicular (644.6 ± 159.8 MPa)^B orientations. While glazing did not have a significant effect on the strength for both orientations, the glazed perpendicular specimen (622.8 ± 96.7 MPa)^B presented similar strength to the glazed parallel specimens (580.9 ± 116.9 MPa)^B.

Conclusion: Both printing layer orientation and finishing protocol affect the fracture strength of 3D-printed 5Y-PSZ. Despite some differences, polishing and glazing are acceptable surface finishing protocols for 3D-printed ceramic restorations in terms of strength.