## 3 Results and Discussion
\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} **Density** \\ **(g/cm\({}^{3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Porosity** \\ **(\%)** \\ \end{tabular} &
\begin{tabular}{c} **Water** \\ **Absorption** \\ \end{tabular} \\ \hline \multirow{4}{*}{Alglass} & 0 & 2.6 \(\pm\) 0.03 & 29.4 \(\pm\) 0.6 & 9.9 \(\pm\) 0.2 \\  & 6 & 2.8 \(\pm\) 0.04 & 16.1 \(\pm\) 3.9 & 5.4 \(\pm\) 1.3 \\  & 12 & 2.8 \(\pm\) 0.04 & 13.4 \(\pm\) 2.6 & 4.5 \(\pm\) 0.8 \\ \hline \multirow{4}{*}{In-ceram} & 0 & 2.6 \(\pm\) 0.08 & 33.1 \(\pm\) 2.2 & 11.1 \(\pm\) 1.0 \\  & 6 & 2.6 \(\pm\) 0.23 & 21.0 \(\pm\) 11.7 & 7.3 \(\pm\) 4.3 \\  & 12 & 2.8 \(\pm\) 0.06 & 13.6 \(\pm\) 11.6 & 4.5 \(\pm\) 3.8 \\ \hline \multirow{4}{*}{Vitro-ceram} & 0 & 2.7 \(\pm\) 0.01 & 28.1 \(\pm\) 2.8 & 9.0 \(\pm\) 0.09 \\  & 6 & 2.7 \(\pm\) 0.34 & 18.8 \(\pm\) 5.5 & 6.9 \(\pm\) 1.6 \\ \cline{1-1}  & 12 & 2.8 \(\pm\) 0.07 & 0.2 \(\pm\) 0.1 & 0.14 \(\pm\) 0.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Infiltration time, density, porosity and water absorption of sintered and infiltrated alumina preforms. According to the Tukey test at a 5% probability level (Table 4), the densities of the Alglass showed no statistically significant difference when infiltrated by periods of 6 and 12 h but showed differences concerning the control group (without infiltration). However, Vitro-ceram and In-ceram samples, when compared with the control group, do not show a statistically significant difference between 6 and 12 h time of infiltration. With regard to porosity, there was no statistically significant difference for the different times of infiltrations for the Alglass and In-ceram samples. In contrast, the Vitro-ceram presented a statistically significant difference related to the infiltration time, where there was a significant reduction in porosity at the infiltration of 12 h than 6 h.  
Considering water absorption, the Vitro-ceram showed a statistically significant difference with the infiltration times of 6 and 12 h and with the control group, showing a significant reduction in water absorption after infiltration. The control group corresponds to the sintered samples from each Al\({}_{2}\)O\({}_{3}\) commercial powder without PMMA-infiltration. For the Alglass and In-ceram samples, there was no influence, statistically, in relation to the times of 6 and 12 h of infiltration, but a difference (reduction) was observed with regard to the control group. This statistical analysis shows that changing the infiltration time has significantly influenced the properties of Vitro-ceram (porosity content and water absorption), whereas it does not affect Alglass and In-ceram. The results for the mechanical tests are summarized in Table 5. The strength values observed for sintered samples are lower than those of infiltrated alumina because of the higher porosity [18]. After 6 and 12 h of infiltrations, all the samples showed a significant increase in strength ranging from 83% (for Alglass) to 218% (for Vitro-ceram). However, the values for Alglass and In-ceram are below those specified by ISO standard 6872 and close to PMMA (25 MPa), for example, at least 100 MPa for monolithic ceramic for a single-unit anterior or posterior prostheses adhesively cemented in the confection of infrastructure in fixed prostheses. According to [PERSON] et al. [19], during monomer conversion to polymer (PMMA), an approximately 20% volume reduction occurs. In this case, this volume reduction in the infiltrated polymer in the alumina matrix creates voids due to the spatial separation between the two materials that diminish the composite ability to withstand higher applied loads [20]. However, the Vitro-ceram sample could be potentially selected for use in metal-free structures, for crowns and fixed partial prostheses. This can be supported by the good bending resistance and microhardness (119 MPa and HV 1055, respectively) [21].