Isotropic pressure-assisted defect regulation of PµSL-printed 5Y-ZrO 2 for high-reliability ultrathin dental veneers

Abstract Projection micro-stereolithography (PmSL) enables individualized zirconia ceramic restorations with complex freeform geometries and hundred-micrometre-scale thicknesses However, PmSL-printed ceramics often retain residual porosity, interlayer heterogeneity, and printing-induced defects after debinding, which limits full densification by conventional pressureless sintering. This limitation is particularly critical for ultrathin veneers because their reduced load-bearing thickness and intricate anatomical geometries increase sensitivity to residual pores, layer defects, and dimensional deviations. Although higher sintering temperatures can promote diffusion-driven densification, they also accelerate grain coarsening, which is detrimental to 5Y-ZrO2 ceramics with limited transformation-toughening capability. Here, an isotropic pressure-assisted densification (iPAD) strategy was developed to regulate densification, defect chemistry, and microstructural uniformity in PmSL-printed 5Y-ZrO2 ceramics. In this process, the PµSL-printed specimens were first pre-sintered and then further densified at elevated temperature under isotropic argon pressure to promote residual-pore closure and improve the overall properties of the ceramics. The optimized iPAD-treated ceramics achieved a relative density of 98.90%, together with a flexural strength of 951.30 ± 71.05 MPa, a Vickers hardness of 13.60 ± 0.07 GPa, a fracture toughness of 4.06 ± 0.30 MPa×m1/2 and a transmittance of 56.15 ± 1.11% at 555 nm. XPS, EPR, TEM, and nanoindentation analyses reveal that the complete iPAD route results in a lower relative abundance of oxygen-vacancy-related defect states, reduces defect-related scattering centers, and improves nanoscale mechanical uniformity. For ~80 µm zirconia veneers, iPAD increased the fracture load by approximately 35% while maintaining high manufacturing accuracy. This work provides a defect-regulated densification paradigm for high-reliability PmSL-printed 5Y-ZrO2 ultrathin dental veneers.