3D Digitally Printed Zirconia Dicalcium Silicate Biomaterial for Dental Applications: Mechanical and Cytocompatibility Testing

Digital Light Processing (DLP) 3D printing enables fabrication of dense, patient-specific ceramic components with high dimensional accuracy, but design rules for bioactive zirconia–calcium-silicate (Zr–CS) composites remain poorly defined. Here, high-solid-loading DLP was used to manufacture dense Zr–CS discs containing 0, 10, 30, and 50 wt.% dicalcium silicate (Ca₂SiO₄), which were debound and sintered at 1300 °C. Microstructural analysis showed progressive pore formation and grain boundary separation with increasing CS content. Compressive strength for CS-containing composites increased from 82.63 to 122.04 MPa between 10 and 50 wt.% CS (p < 0.05), but remained lower than pure zirconia (170.19 MPa). In contrast, Young’s modulus and Vickers hardness decreased monotonically with CS addition, reflecting the higher porosity and microstructural discontinuities. Indirect-contact assays with human mesenchymal stem cells (hMSCs) showed that 10 wt.% CS maintained metabolic activity comparable to control, whereas 30–50 wt.% CS significantly reduced metabolic activity after 4 days of eluate exposure (p < 0.05). Direct-contact experiments corroborated this trend: cells attached and spread well on pure Zr and 10 wt.% Zr–CS, but coverage and nuclear count were markedly reduced at ≥30 wt.% CS. By combining quantitative porosity, mechanical properties, and dual-mode cytocompatibility on the same sintered parts, this work identifies a practical design window for dense Zr–CS composites: ≤10 wt.% CS balances structural integrity with cytocompatibility, while higher CS fractions primarily serve as boundary compositions defining mechanical and biological limits. High-solid-loading DLP Zr–CS composites therefore offer a route to bone-relevant stiffness tuning and controlled bioactivity for next-generation dental implants.