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 ( TP 00 ), color difference ( ΔE 00 ), 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 ( ΔTP 00 and ΔE 00 below perceptibility threshold; strength >800 MPa). Initial RZP and 3-DM samples showed microstructural flaws, leading to poorer mechanical and esthetic outcomes. • Residual zirconia blocks (4YSZ) were recycled into zirconia powders, which were effectively refined via wet milling with smaller beads, improving their sinterability. • The sintered bodies derived from the optimized powders exhibited microstructural integrity and esthetic properties comparable to commercial zirconia ( ΔTP 00 and ΔE 00 < perceptibility thresholds). • The recycled zirconia achieved a biaxial flexural strength exceeding 800 MPa, demonstrating its potential for clinical application in esthetic dental restorations.