Polishing of 4Y- and 5Y- zirconia: effects on roughness, color and gloss.

OBJECTIVES: To investigate the effects of polishing systems on the roughness, gloss and color of two zirconia materials as a function of the rotational speed and number of polishing movements. MATERIALS AND METHODS: Specimens (n = 8/group) from 4Y-TZP and 5Y-TZP were milled, diamond grinded and polished. The intraoral polishing varied in the number of polishing steps, the grain size and the matrix. Different number of polishing movements and rotation speed were used. Roughness (ISO25178-2:2021), gloss (ISO2813:2014) and color stability (ISO/CIE 11664-4:2019) were determined. STATISTICS: Shapiro-Wilk, one-way analysis, Bonferroni, Pearson, variance analysis/intermediate sub-effects (α = 0.05). RESULTS: Roughness Sa varied between 2.45 ± 0.93 µm and 6.47 ± 0.26 µm (4Y-TZP) and 2.31 ± 0.19 µm and 6.54 ± 0.22 µm (5Y-TZP). Maximum roughness Sz ranged from 32.92 ± 12.59 µm to 99.32 ± 19.87 µm (4Y-TZP) and 31.45 ± 3.02 µm to 90.75 ± 12.59 µm (5Y-TZP). Different gloss from 28.9 ± 4. 23 to 102.39 ± 18.63 GU (4Y-TZP) and 33.19 ± 3.68 to 101.28 ± 10.00 GU (5Y-TZP) was found. ΔE results ranged from 0.39 ± 0.34 to 6.30 ± 1.22 (4Y-TZP) and 0.87 ± 0.71 to 7.50 ± 1.67 (5Y-TZP). Significant (p ≥ 0.095) intermediate sub-effects were found. CONCLUSIONS: Polishing led to a reduction in roughness, an increase in gloss and a significant change in color. Polishing had a stronger effect on 5Y-TZP. CLINICAL RELEVANCE: The correct use of the polisher type (stages, binder) and its specific application (rotational speed, movements) can improve roughness, gloss and color variations.