Flashing digital light processing based functionally graded additive manufacturing of zirconia dental crowns with simultaneous color and translucency gradation

In this work, we present a digital light processing (DLP)-flashing-based functionally graded additive manufacturing (FGAM) process for fabricating highly aesthetic zirconia (ZrO₂) dental crowns with simultaneous color and translucency gradation. Color gradation was achieved by controlled iron oxide (Fe₂O₃) doping (ranged from 0.0 to 0.10 wt%) in zirconia powders, whereas translucency gradation was simultaneously attained by controlling the isotropic cubic phase (c-ZrO₂) in the sintered crowns using three different grades of yttria-stabilized ZrO₂ (3, 4, and 5 mol% yttria-stabilized ZrO₂ powders, i.e., 3YSZ, 4YSZ, and 5YSZ, respectively). The crowns were printed through flashing illumination: 0.2 s flash time and 1 s off-time between consecutive ultraviolet (UV) flashes to overcome the scattering-induced overcuring associated to continuous printing that degraded the structural accuracy of the design and posed post-processing challenges and property deterioration. International Commision on Illumination’s Lab (CIELAB) color assessments indicated successful coloring indices (L*, a*, and b* values) matching the graded appearance of natural teeth. Mechanical properties and sintering shrinkage were slightly affected by the Fe₂O₃ and yttria contents of the various compositions. The highest translucency parameter (above 20) was possible with an undoped 5YSZ composition at the top part (incisor) of the crown. The processing challenges during FGAM of ceramic materials were successfully overcome through a flashing mechanism, and the color and translucency gradation of the ZrO₂ dental crown was simultaneously maintained with enhanced printing precision, which is a potential breakthrough advancement in esthetic dentistry.