Surface Characteristics and Flexural Strength of Porous-Surface Designed Zirconia Manufactured via Stereolithography

Purpose To design and fabricate zirconia bars with porous surfaces using stereolithography and evaluate their surface characteristics and flexural strengths. Materials and Methods Five groups of zirconia bars (20 mm x 4 mm x 2 mm) with interconnected porous surfaces were designed and manufactured: (i) 400-mu m pore size and 50% porosity (D400-P50 group), (ii) 400-mu m pore size and 30% porosity (D400-P30 group), (iii) 200-mu m pore size and 50% porosity (D200-P50 group), (iv) 200-mu m pore size and 30% porosity (D200-P30 group), and (v) 100-mu m pore size and 30% porosity (D100-P30 group). Zirconia bars without a porous surface (NP) were used as controls. The surface topographies and pore structures were investigated using scanning electron microscopy and three-dimensional laser microscopy. The printed porosity was calculated using the Archimedes method. Fifteen specimens from each group were subjected to a three-point bending test according to the ISO 6872:2015 standard. A Weibull analysis was performed, and the fractured surfaces were examined using scanning electron microscopy. Results Zirconia bars with porous surfaces were designed and successfully manufactured. The designed pore size, porosity, and shape of the printed pores were approximately achieved for all the porous surfaces. The flexural strength of the control group was significantly higher than those of the groups with porous surfaces (p < 0.001). For the same porosity, groups with a pore size of 400 mu m exhibited a lower flexural strength than the other groups (p<0.001). Additionally, for the same pore-size design, the flexural strengths of group D400-P50 and D400-P30 exhibited no significant differences (p = 0.150), while the flexural strengths of D200-P30 were significantly higher than that of the D200-P50 group (p = 0.043). The control group and D400-P50 group had higher Weibull moduli than the other groups. The fractography of the specimens with porous surfaces indicated more than one crack origin, mainly owing to defects, including pores and cracks. Conclusion Zirconia bars with porous surfaces were successfully designed and fabricated using the stereolithography technique. Although porous surfaces may be advantageous for osteogenesis, the porous-surface design can reduce the flexural strength of the printed zirconia bars. By reducing the pore size, controlling the porosity, and improving the printing accuracy, a higher strength can be achieved.