Color eye 7000a

A spectrophotometer was used to measure the reflectance values (Color-Eye^® 7000A, X-Rite, Carlstadt, NJ, USA). As per the manufacturer’s recommendations, a black trap and white tile were used to calibrate the spectrophotometer. A port was used to stabilize the specimens, and the white or black reference material was supported at the back of the specimens to keep the arm closed. The color measurements of the coordinates (L*, a*, b*) using the Commission Internationale de l’Eclairage system were obtained for the discs against the white and black backgrounds, and the system automatically provided the average. The tabulated data were used to calculate the translucency (TR) ratio, and the following equation was used to obtain the results:

Baseline shades of all teeth were measured using a wave dispersion spectro-photometer (Color-Eye 7000A, X-Rite Gmbh, Regensdorf, Switzerland). The samples were removed from the solution at 4, 8, 4, 48 and 72 h and rinsed with distilled water. Shade was measured on the exposed labial surface using the protocol developed by Lee et al. [14 (link)] to obtain the CIE l*a*b values for change in color. The change in color ΔE was calculated using the formula $\mathrm{\Delta }{E}_{\mathrm{ab}}=\sqrt{{\left(L_2^{\ast }-L_1^{\ast }\right)}^2+{\left(a_2^{*}-a_1^{*}\right)}^2+{\left(b_2^{*}-b_1^{*}\right)}^2}$ A ∆E >3 (from the baseline score) was recorded as clinically visible staining.

To assess color change, a reflectance spectrophotometer (Color-Eye 7000A; X-rite, Grand Rapids, MI, USA) was utilized. The Commission Internationale de l’Elcairage (CIE) L*a*b*color scale was employed to quantity the color of the test samples before and after the pH-cycling model. The CIE Lab* system constitutes a three-dimensional color space, where L* represents lightness on a scale of zero to 100, ranging from black to white. On the other hand, a* and b* represent chromaticity without specific numerical boundaries. Negative a* values indicate green shades, positive a* values indicate red shades, negative b* values correspond to blue shades, and positive b* values correspond to yellow shades [26 (link)]. The three color coordinates were documented at the two distinct time intervals, and ΔE* values were computed by employing the formula to measure the color difference before and after the pH-cycling model [26 (link)]:
${\mathrm{\Delta }E}^{*}={\left[{\left({\mathrm{\Delta }L}^{*}\right)}^2+{\left({\mathrm{\Delta }a}^{*}\right)}^2+{\left({\mathrm{\Delta }b}^{*}\right)}^2\right]}^{1/2}$

Color measurements were obtained with a standard illuminant C and calibrated spectrophotometer (Color-Eye^® 7000 A, X-Rite, Carlstadt, NJ, USA) in the visible spectrum range (380–780 nm) [32 (link),34 (link)]. The color difference between the specimens was calculated using the following equation: $$\Delta {\mathrm{E}}_{00}=\sqrt{{\left(\frac{\Delta {\mathrm{L}}^{\prime }}{{\mathrm{K}}_{\mathrm{L}}{\mathrm{S}}_{\mathrm{L}}}\right)}^2+{\left(\frac{\Delta {\mathrm{C}}^{\prime }}{{\mathrm{K}}_{\mathrm{C}}{\mathrm{S}}_{\mathrm{C}}}\right)}^2+{\left(\frac{\Delta {\mathrm{H}}^{\prime }}{{\mathrm{K}}_{\mathrm{H}}{\mathrm{S}}_{\mathrm{H}}}\right)}^2+{ \mathrm{R}}_{\mathrm{T}}\left(\frac{\Delta {\mathrm{C}}^{\prime }}{{\mathrm{K}}_{\mathrm{C}}{\mathrm{S}}_{\mathrm{C}}}\right) \left(\frac{\Delta {\mathrm{H}}^{\prime }}{{\mathrm{K}}_{\mathrm{H}}{\mathrm{S}}_{\mathrm{H}}}\right)}$$
where ΔL′, ΔC′, and ΔH′ are the differences in lightness, chroma, and hue between the control and modified specimens, R_T is a function that accounts for differences in chroma and hue in the blue region, and S_L, S_C, S_H adjust for variation in the location of color difference of samples in L′, a′, b′ values, while K_L, K_C, K_H are correction terms set at 2:1:1 [15 (link),32 (link),33 (link)]. ΔE₀₀ was assessed on perceptibility (PT) basis and acceptability (AT) thresholds, which were set at 50:50%; PT ranged from 0.8 to 1.30 and 50:50% AT ranged from 1.80 to 2.25 ΔE₀₀ [35 (link)].

For color analysis, color measurements were recorded with the help of a reflectance spectrophotometer (Color-Eye® 7000A, X-Rite) and CIE L^∗a^∗b^∗ color scale (Commission Internationale de I'Eclairage) using standard illuminant (D65) in the wavelength range of 360–740 nm. The three color coordinates were recorded at each time interval, and ΔE was calculated (between baseline and different immersion durations) using the formula ΔE^∗=[(ΔL^∗)²+(Δa^∗)²+(Δb^∗)²]^1/2 [2 , 15 (link)]. The mean values were compared in terms of tested material, aging methods (immersion solution), and duration. Color changes (ΔE) were converted to National Bureau of Standards (NBS) units [10 (link), 15 (link)] using the formula: NBS units = ΔE × 0.92 and correlated with the corresponding meaning [15 (link), 16 ].

The digital spectrophotometer (Color-Eye 7000A; X-rite, Grand Rapids, MI, USA) was used to capture the color changes by differentiating the transmitted and reflected light beam for each specimen using CIE L*a*b* [20 (link)]. To analyze the color stability of each specimen, the following equation was used: $∆E={[∆L{(L-L^{*})}^{2 }+∆a{(a-a^{*})}^2+∆b{(b-b^{*})}^2]}^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$ [21 (link)] (color changes (∆E) and color variables (L*, a*, b*). To apply the color changes in this research in a clinical situation, a formula was used to convert the color changes (∆E) to National Bureau of Standards (NBS) units (NBS units = E × 0.92). The formula used to classify the clinically acceptable color changes is as follows: indicial (NBS = 0.0–0.5); slight (NBS = 0.5–1.5); noticeable (NBS = 1.5–3.0); considerable (NBS = 3.0–6.0); very (NBS = 6.0–12.0); and excessive (NBS = +12.0) [22 (link)].