Illuminant-dependent color inconstancy and metameric behavior of anodized titanium through silicone-based gingival...

This in vitro study evaluated how gingival thickness and anodization color affect color perception of Grade V titanium discs under different light sources. Ninety-six titanium discs were anodized yellow, pink, or purple, or left non-anodized. Silicone gingival masks of 1 mm and 2 mm simulated soft tissue. A single spectral reflectance measurement was recorded for each specimen using a benchtop spectrophotometer, from which color coordinates under five standardized illuminants (D65, D50, A, F2, F11) were computationally derived. Color differences (ΔE₀₀) were calculated using the CIEDE2000 formula to evaluate color inconstancy, and metamerism was quantified using a CIEDE2000-based metamerism index (MI), the mean absolute difference between ΔE₀₀ under the test illuminants (D50, A, F2, F11) and D65. Data were analyzed with one-way ANOVA, Tukey HSD post hoc tests, and independent t-tests (α = 0.05). All anodized colors at 1 mm exceeded the CIEDE2000 clinical acceptability threshold (ΔE₀₀ >1.8), with purple showing the highest inconstancy, particularly under fluorescent lighting (P<.05). Increasing thickness to 2 mm significantly reduced ΔE₀₀ across all groups (P<.05), although values remained above the acceptability threshold in every group, with purple showing the greatest relative stability under all illuminants. Metameric behavior remained imperceptible under most conditions, except for pink at 1 mm under F2. Thickness and lighting significantly affect color stability of anodized titanium, although the effect of illuminant type was color-dependent: fluorescent (F2) illumination increased color inconstancy for purple and, at 2 mm, yellow, whereas pink showed the opposite pattern, with its lowest ΔE₀₀ values occurring under F2 rather than D65 at both thicknesses. Thinner tissue intensifies color shifts, while ≥ 2 mm thickness improves consistency. Pink performs better in thin tissue; purple shows greatest stability with thicker coverage. Metamerism was imperceptible under most conditions, except for pink at 1 mm under F2, which reached a perceptible but clinically acceptable level.