[Effect of porous surface structure on fatigue strength of 3D printed zirconia]

To study the effect of porous surface structure on fatigue strength of zirconia fabricated by stereolithography apparatus (SLA), and to provide reference for the surface design of 3D printed zirconia implants.

Zirconia specimens were fabricated by SLA. According to the surface structure, zirconia specimens were divided into non-porous group, 200 μm group and 400 μm group. The surface morphology was observed by 3D laser morphology microscope and scanning electron microscope, and the surface roughness, pore parameters and grain size were measured. The flexural strength of the specimen was measured by three-point bending test and Weibull analysis was performed. The fatigue strength of the specimens was measured by fatigue test, and the fatigue mechanism was analyzed by fractrography. The crystal phase before and after fatigue test of the specimen was analyzed by X-ray diffraction.

The surface roughness of the area between the pores of non-porous group, 200 μm group and 400 μm group was (0.79±0.09) μm, (0.81±0.16) μm and (0.81±0.09) μm, respectively, with no significant difference among them. The surface grain size was (324.11±21.38) nm, (308.06±11.34) nm, (311.62±15.02) nm, respectively, with no significant difference among them. The results of three-point bending test showed that the three-point bending strength of the non-porous group [(1 030.70±111.71) MPa] was significantly higher than that of the porous groups (P < 0.001). The 200 μm group [(272.04±61.16) MPa] was significantly higher than the 400 μm group [(201.21±25.58) MPa] (P < 0.01). The fatigue strength of the non-porous group [(702.29± 21.62) MPa] was significantly higher than that of the porous groups (P < 0.001), and the fatigue strength of the 200 μm group [(159.57±9.30) MPa] was significantly higher than that of the 400 μm group [(125.36±6.11) MPa] (P < 0.001). The fracture analysis results showed that the crack origins were mainly internal defects, air holes, inclusions and the joint of printing layer, etc. There was no significant difference in the content of monoclinic phase before and after fatigue test among all the groups.

The surface porous microstructure could significantly reduce the fatigue strength of the zirconia specimens, and the larger pore size showed the lower fatigue strength. In the future, the material and printing process of 3D printing zirconia should be improved, and the surface structure design should be further optimized to improve the mechanical properties of 3D printing zirconia.