Stainability of Polished and Glazed Printed Monolithic Zirconia After Coffee Thermocycling

This study assessed the impact of the method of manufacturing, surface treatment, and thickness on the stainability of zirconia after thermocycling.

Twenty 0.5 × 10 mm and 20 1 × 10 mm zirconia disks were fabricated using a milling machine. Also, 20 0.5 × 10 mm and 20 1 × 10 mm zirconia disks were fabricated using a 3D printer. After sintering, samples were subjected to one of the two surface treatments (n = 10). Eight study groups were arranged as (1) 0.5 mm printed-polished, (2) 1 mm printed-polished, (3) 0.5 mm printed-glazed, (4) 1 mm printed-glazed, (5) 0.5 mm milled-polished, (6) 1 mm milled-polished, (7) 0.5 mm milled-glazed, and (8) 1 mm milled-glazed. CIELab values were measured with a spectrophotometer before and after 10,000 thermal cycles in coffee solution. ΔE₀₀ readings were compared with perceptibility (< 0.8) and acceptability (< 1.8) thresholds. Data were analyzed using three-way ANOVA and the Games-Howell test (α = 0.05).

Although all mean ΔE₀₀ values were below the acceptability threshold, only 1 mm printed-glazed zirconia and all milled zirconia samples, except for the 0.5 mm polished group, were below the perceptibility threshold. A significant interaction was found between the production method, surface treatment, and thickness (p = 0.002); 0.5 mm printed zirconia, either polished or glazed, and also 1 mm polished printed zirconia exhibited significantly higher ΔE₀₀ than their milled counterparts. Moreover, glazing significantly reduced stainability in all zirconia specimens (p < 0.05). Also, 1 mm milled-polished zirconia had a lower ΔE₀₀ value than its 0.5 mm counterpart (p = 0.038).

Printed zirconia had less color stability than milled zirconia. Glazing provided the lower color change for both milled and printed zirconia. Thicker milled-polished zirconia had a better color stability.

Although the color stainability of printed zirconia was more than milled zirconia, it showed clinically acceptable color change values along with the milled zirconia, regardless of the method of surface treatment and thickness.