Preparation of recycled zirconia powders for use in esthetic dental restorations by wet ball milling technique

This study aimed to optimize ball milling conditions for preparing recycled zirconia powder (RZP) for esthetic dental restorations. Initial RZP and four ball milling groups, including 3-WM (3 mm beads, wet milling), 3-DM (3 mm beads, dry milling), 5-WM (5 mm beads, wet milling), and 5-DM (5 mm beads, dry milling), were characterized. The sintered samples were compared with commercial zirconia in terms of the microstructure, transmittance, translucency parameter (TP₀₀), color difference (ΔE₀₀), density, hardness, fracture toughness, and biaxial flexural strength. Smaller beads enabled more effective RZP refinement. Wet milling proved superior to dry milling in achieving finer particles and reducing crystal defects. Recycled zirconia sintered from 3-WM powders, particularly after 3 h of milling, exhibited microstructure, optical, and mechanical properties comparable to commercial zirconia (ΔTP₀₀ and ΔE₀₀ below perceptibility threshold; strength >800 MPa). Initial RZP and 3-DM samples showed microstructural flaws, leading to poorer mechanical and esthetic outcomes.