# Colour Changes of Acetal Resins (CAD-CAM) In Vivo
## 3 Results  
Table 1 shows the colour changes, according to the \(\Delta\)Eab* formula and the \(\Delta\)E00* formula, between the day of placement of the provisional hybrid POM prosthesis and after the different weeks of follow-up in the three thirds of the tooth. The highest colour difference according to the \(\Delta\)Eab* formula was 27.46 units after 15 weeks of follow-up and occurred in the cervical third. On the other hand, the lowest shade difference was 7.34 units after 17 weeks of follow-up and took place in the incisal third. These colour differences exceeded the threshold of clinical acceptability (Figure 2) proposed by [PERSON] et al. [27]. According to the \(\Delta\)E00* formula, the lowest colour change was 5.23 units, and the highest colour change was 22.61 units (Figure 3). The pH range varied from 6 to 9 units and the follow-up weeks ranged from a minimum of 6. to a maximum of 31. Figure 1: Scheme of the methodology. With both formulas, the ANOVA with one factor of variation (thirds of the tooth) in a randomised block design (subjects) revealed that the chromatic changes in the three areas differed significantly (\(p\) = 0.002). Subsequently, [PERSON]'s test showed that discolourations \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**CIELAB (\(\Delta\)Eab*)**} & \multicolumn{3}{c}{**CIEDE2000 (\(\Delta\)E00*)**} \\ \hline \multirow{2}{*}{**Participants**} & **Cervical** & **Middle** & **Incisal** & **Cervical** & **Middle** & **Incisal** & **prefs of** \\  & **\(\Delta\)Eab* & **\(\Delta\)Eab* & **\(\Delta\)Eab* & **\(\Delta\)E00* & **\(\Delta\)E00* & **\(\Delta\)E00* & **\(\Delta\)E00* & **\(\Delta\)E00* & **\(\Delta\)E00* \\ \hline
1 & 24.92 & 25.09 & 19.67 & 21.06 & 20.37 & 16.29 & 6 & 16 \\
2 & 17.44 & 13.88 & 18.98 & 15.04 & 11.07 & 16.21 & 6.5 & 12 \\
3 & 18.71 & 19.36 & 20.16 & 15.88 & 16.28 & 17.48 & 7 & 31 \\
4 & 18.24 & 16.29 & 9.63 & 16.41 & 13.57 & 8.40 & 6 & 14 \\
5 & 16.01 & 15.13 & 11.10 & 13.75 & 12.23 & 8.81 & 8 & 27 \\
6 & 15.49 & 17.02 & 14.15 & 13.01 & 13.13 & 10.84 & 9 & 18 \\
7 & 19.51 & 21.14 & 17.77 & 18.20 & 17.76 & 14.51 & 8.5 & 18 \\
8 & 11.01 & 12.01 & 11.42 & 8.68 & 9.53 & 9.36 & 6.5 & 6 \\
9 & 9.87 & 9.21 & 7.34 & 8.16 & 6.72 & 5.23 & 6 & 17 \\
10 & 18.03 & 16.50 & 13.97 & 14.97 & 13.47 & 11.45 & 9 & 15 \\
11 & 23.71 & 25.59 & 19.81 & 18.70 & 19.28 & 13.43 & 7.5 & 15 \\
12 & 10.58 & 10.75 & 9.54 & 7.65 & 7.81 & 6.96 & 8 & 15 \\
13 & 27.46 & 23.86 & 15.35 & 22.61 & 18.38 & 11.20 & 7.5 & 15 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Colour differences, according to the Euclidean and CIEDE2000 formulae, in the three thirds of the upper central incisor. Figure 3: Colour differences (\(\Delta\)Eab* and \(\Delta\)E00*) exceeded the threshold of clinical acceptability. Figure 2: Color difference between A3 dental shade tab and hybrid provisional complete prothesis made of acetal resin. in the cervical and middle areas did not differ significantly, but discolourations in the incisal area did, where colour changes were significantly smaller. By using regression models, it was assessed whether the degree of discolouration was significantly related to the weeks of follow-up and to pH, according to the two colour formulae in each of the tooth thirds. Euclidean formula (\(\Delta\)Eab*):  
\[\widehat{\text{Dif cervical}}=16.379-0.034\text{pH}+0.097\text{ Weeks of follow up }(\text{R}^{2}=0.012)\]  
\[\widehat{\text{Difmiddle}}=12.561+0.363\text{pH}+0.127\text{ Weeks of follow up }(\text{R}^{2}=0.032)\]  
\[\widehat{\text{Difincisal}}=11.493+0.090\text{pH}+0.141\text{ Weeks of follow up }(\text{R}^{2}=0.041)\]  
In all three areas, the coefficients of determination were small, which indicates that discolouration depends on explanatory variables other than pH and follow-up weeks. However, an increase in the coefficient of determination was observed from the cervical to the incisal area. No model was significant (tests for significance of regression with \(p>0.05\)).