Zirconia materials are widely used in digital dentistry due to their excellent properties. Although zirconia prostheses are typically prepared using computer-aided design and manufacturing, additive manufacturing technology can also be used. Both digital methods, however, may result in a large amount of residue zirconia. In the present study, solvent-based slurry stereolithography was used to prepare dental zirconia samples using either pristine or recycled zirconia powder. Characteristics of pristine zirconia, recycled powder, and as-prepared slurry were examined. Whereas, the 3D-printed objects using each material were built up with a layer thickness of either 20 or 40 μm. Post heat treatment was performed to improve the mechanical properties. Density measurement, Vickers microhardness, and flexure strength of the sintered zirconia samples were investigated. Experimental results showed that the agglomeration of zirconia occurs in recycled powder and increases the viscosity of the slurry. The sintered zirconia samples exhibited a density higher than 99% when using the pristine powder and printed with a thickness of 20 μm, whereas the recycled powder printed with 40 μm thickness had a density slightly higher than 90%. The Vickers microhardness (~1300 HV) was similar for sintered samples, but the flexure strength was significantly different. The flexure strength can reach up to 1057 MPa using pristine powder and printed with a layer thickness of 20 μm, but decrease to 389 MPa when using recycled powder with 40 μm layer thickness. The results suggest that 3D-printed zirconia using pristine powder can be used as dental prostheses, whereas 3D-printed zirconia using recycled powder may only be suitable for incisors or other applications.
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