Additively Manufactured Zirconia for Dental Applications with In Situ Color Gradation Control

The current process for creating zirconia reconstructions for teeth is time-consuming, expensive, and results in tool wear and raw material waste. An alternative method, near-net shape additive manufacturing capable of producing samples with color gradient is presented as an innovative and more efficient solution. A low-cost robocasting system, which enabled the co-extrusion of two different ceramic inks, was designed and developed. Moreover, hydrogel-based ceramic inks, with rheological properties suitable for the present system, containing commercially available Yttria-stabilized zirconia (white and yellow) powders, were produced. Parts of different color shades and color gradients, with a high aspect ratio and good green body stability, were printed. In addition, precise color measurements were carried out, and co-extruded parts were compared with ultraviolet-C photofunctionalized parts. High fractions of binder in green bodies caused distortions in the samples during air drying and upon sintering. Debinding and sintering at 1500°C yielded parts of relatively low density (4.90-5.09 g/cm³) and hardness (500 HV10-1100 HV10). A slightly different sintering behavior was observed for parts of different compositions. Density and hardness increased with the fraction of iron oxide-containing ink.