## 3 Results  
### Analysis of \(\Delta\)E Values  
The descriptive statistics related to the \(\Delta\)E results are presented in Table 1.  
The highest median value found was 8, corresponding to ZZ zirconia using the metal substrate and light cement. The lowest median value was 1.3 in the AG brand, with zirconia as the substrate and glycerol as the cement (Table 1). The \(\Delta\)E values were significantly influenced (\(p<0.05\)) by the type of restoration, substrate, and cement. Statistically significant differences (\(p=0.035\)) were found in the \(\Delta\)E values obtained for the two zirconia brands under study, with the lower median values recorded for the AG brand (2.1) compared to ZZ (4.2) (Figure 12). Regarding the \(\Delta\)E values obtained for the different substrates under study, statistically significant higher levels of \(\Delta\)E (\(p<0.05\)) were observed in metal compared to zirconia (\(p<0.001\)) or natural teeth (\(p<0.001\)), but no significant differences were found between the last two (\(p=0.933\)). The lowest median value recorded was 2.65 for the zirconia substrate, while the highest was 6.00 for the metal substrate (Figure 13). \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Zirconia Brand** & **Substrate** & **Cement** & \multicolumn{4}{c}{\(\Delta\)E} \\  & & & **M** & **SD** & **Mdn** & **IR** & **Group Differences** \\ \hline \multirow{6}{*}{Amann Girrbach (AG)} & \multirow{2}{*}{Metal} & Glycerol & 7.1 & 0.30 & 7.0 & 7.00 & b \\  & Light & 7.1 & 0.20 & 7.1 & 7.55 & b \\  & Neutral & 5.8 & 0.30 & 5.8 & 5.75 & a \\ \cline{2-6}  & \multirow{2}{*}{Zirconia} & Glycerol & 1.3 & 0.10 & 1.3 & 1.30 & a \\  & Light & 1.9 & 0.10 & 1.9 & 1.95 & b \\  & Neutral & 1.7 & 0.10 & 1.8 & 1.65 & a, b \\ \cline{2-6}  & \multirow{2}{*}{Tooth} & Glycerol & 2.1 & 0.20 & 2.1 & 1.80 & a \\  & Light & 1.9 & 0.10 & 1.9 & 1.85 & a \\  & Neutral & 2.5 & 0.20 & 2.5 & 2.20 & a \\ \hline \multirow{6}{*}{Zirkonzahn (ZZ)} & \multirow{2}{*}{Metal} & Glycerol & 4.5 & 0.20 & 4.5 & 4.50 & a \\  & Light & 8.0 & 0.60 & 8.0 & 7.90 & b \\  & Neutral & 3.8 & 0.10 & 3.8 & 3.90 & a \\ \cline{2-6}  & \multirow{2}{*}{Zirconia} & Glycerol & 3.7 & 0.10 & 3.7 & 3.60 & a \\  & Light & 4.6 & 0.10 & 4.7 & 4.60 & b \\  & Neutral & 4.1 & 0.20 & 4.1 & 4.40 & a, b \\ \hline \multirow{6}{*}{Tooth} & Glycerol & 4.1 & 0.10 & 4.1 & 4.00 & a \\  & Light & 5.6 & 0.20 & 5.6 & 5.65 & b \\ \cline{1-1}  & Neutral & 3.5 & 0.10 & 3.5 & 3.45 & a \\ \hline \end{tabular}  
* Identical letters represent no significant differences between cements in each brand/substrate combination (\(p>0.05\)).  
\end{table} 
Table 1: Mean (M) values, standard deviations (SD), medians (Mdn), and interquartile ranges (IR) of color differences (\(\Delta\)E) for each experimental group. Statistically significant differences (\(p<0.05\)) were also observed in the \(\Delta\)E values obtained for the studied cements. However, no significant differences were found between glycerol and light cement (\(p=0.072\)) or neutral cement (\(p=1.000\)). Statistically significant lower levels of \(\Delta\)E values were detected in neutral compared to light cements (\(p=0.032\)). The lowest median value recorded was 3.65 for neutral cement, while the highest was 4.60 for light cement (Figure 14). For brand AG and the metal substrate, statistically significant lower levels of \(\Delta\)E (\(p<0.05\)) were detected using neutral cement compared to both light cement and glycerol, whereas they did not show significant differences between them (\(p>0.05\)) (Table 1). Regarding the ZZ brand restorations and the metal substrate, statistically significantly higher levels of \(\Delta\)E (\(p<0.05\)) were found using light cement compared to both neutral cement and glycerol, while no significant differences were observed between them (\(p>0.05\)) (Table 1).