## 3 Results and Discussion
Figure 5: (**a**) Alglass, (**b**) Vitro-ceram and (**c**) In-ceram samples before infiltration and sintered at 1400 \({}^{\circ}\)C for 2 h.  
Figure 6: (**a**,**b**) SEM images from the surface, and (**c**) cross-section of Vitro-ceram infiltrated with PMMA for 6 h. (**d**) Sample cross-section image at lower magnification of \(\times\)100 and infiltration for 12 h.  
The data for the water absorption, bulk density and porosity content of the sintered and infiltrated samples are summarized in Table 3. A reduction in the apparent porosity and, therefore, water absorption, ranging from 33-50%, is observed for all the samples after infiltration for 6 h and polymerization. A slight increase, considering the standard deviation, in the density is also observed. For a period of 12 h, under the same conditions described above, there was an even greater reduction in the apparent porosity and water absorption from 54 (Alglass) to 99% (Vitro-ceram). A small increase in the value of the density is also recorded, except for Vitro-ceram. The Vitro-ceram is less porous (before and after the infiltration) when compared to the other groups. This can be attributed to the fact that it has been well-pressed (i.e., it has higher density) due to its particle size distribution. According to German [17], the packaging of particles with bimodal size distribution results in higher densities than monomodal distribution packaging. The sample Vitro-ceram presented a range of particle size distributions with a greater number of smaller particles contributing to better packaging, a higher density and smaller pore size after sintering. This favored a more extensive filling of pores by monomer due to the greater capillary force. Table 4 presents the statistical data of physical properties, in which the Tukey test for the comparison of the average values was performed at a significance level of 5%. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \begin{tabular}{c} **Ceramic** \\ **Samples** \\ \end{tabular} & \begin{tabular}{c} **Infiltration** \\ **Time (h)** \\ \end{tabular} & \begin{tabular}{c} **Average of** \\ **Density (g/cm\({}^{3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Average of** \\ **Porosity (\%)** \\ \end{tabular} &
\begin{tabular}{c} **Average of** \\ **Water** \\ **Absorption (\%)** \\ \end{tabular} \\ \hline \multirow{4}{*}{Alglass} & 0 & 2.6 b  & 29.4 a  & 9.9 a  \\  & 6 & 2.8 a  & 16.1 b  & 5.4 b  \\  & 12 & 2.8 a  & 13.4 b  & 4.5 b  \\  & & \(p\) = 0.002 & \(p\) \(<\) 0.001 & \(p\) \(<\) 0.0001 \\ \hline \multirow{4}{*}{In-ceram} & 0 & 2.6 a  & 33.1 a  & 11.1 a  \\  & 6 & 2.6 a  & 21.0 b  & 7.3 ab  \\  & 12 & 2.8 a  & 13.6 b  & 4.5 b  \\  & & \(p\) = 0.04 & \(p\) \(<\) 0.001 & \(p\) = 0.0023 \\ \hline \multirow{4}{*}{Vitro-ceram} & 0 & 2.8 a  & 28.1 a  & 9.0 a  \\  & 6 & 2.5 a  & 18.8 b  & 6.9 b  \\  & 12 & 2.6 a  & 0.2 c  & 0.1 c  \\  & & \(p\) = 0.68 & \(p\) \(<\) 0.001 & \(p\) \(<\) 0.0001 \\ \hline \hline \end{tabular} Note: Equal superscript letters mean statistically equal values and different letters mean statistically different values at a significance level of 5%.  
\end{table} 
Table 4: Comparison of averages for water absorption, apparent porosity and bulk density of independent samples using Tukey test to the 5% level of statistical significance.