Comparison of Masking Ability of Milled and 3D-Printed Monolithic Zirconia on Discolored Substrates

The masking ability of printed zirconia over discolored backgrounds is unknown. This study assessed the impact of method of manufacturing, thickness, and the method of surface treatment on the color masking ability of zirconia.

Forty 0.5 mm × 10 mm and 40 1 mm × 10 mm zirconia disks (Dental Direct Medical Zirconia, Germany) were designed, fabricated using a milling machine (DWX-51D, Roland DGA, Irvine, CA) and a 3D printer (AON 3D printer; ZIPRO dentistry; South Korea), and divided into eight groups: (1) printed-polished, (2) printed-glazed, (3) milled-polished, and (4) milled-glazed. ΔE ₀₀ values between each group and substrates made of natural die composite resin (IPS, IvoclarVivadent, Schaan, Liechtenstein) in shades of ND₁ (control), ND₃, ND₅, and ND₉ were measured. Data were analyzed using three-way ANOVA and Games-Howell tests (α = 0.05).

Printed zirconia with either thickness showed a better masking ability as compared to their milled zirconia. Milled zirconia (0.5 mm) showed the highest ΔE ₀₀ values (ND_3-1: 1.70, ND_5-1: 3.62, ND_9-1: 6.46), while 1 mm printed zirconia had the lowest ΔE ₀₀ values (ND_3-1: 0.73, ND_5-1: 1.71, ND_9-1: 3.04). Moreover, ΔE ₀₀ values of printed zirconia were below the acceptability threshold (< 1.8) for ND₃ and ND₅ substrates, except for 0.5 mm zirconia against the ND₅ substrate.

All zirconia specimens showed clinically acceptable masking ability against a normal dentin shade (ND₃) (< 1.8). Also, printed zirconia (1 mm) against ND₃ substrate showed the highest masking ability. Moreover, only 1 mm printed zirconia over a darker shade of dentin (ND₅) showed a clinically acceptable color difference. However, no zirconia specimen could mask severely discolored dentin (ND₉).