## 4 Conclusions  
The infiltration of sintered Al\({}_{2}\)O\({}_{3}\) (Vitro-ceram) by PMMA for 12 h under the pressure of 7 bar led to the development of a highly filled PMMA/ceramic composite for potential use as a dental prosthesis. The 12-hour infiltration for Vitro-ceram demonstrated a near-zero open porosity and optimum mechanical characteristics, passing the acceptance criteria of ISO 6872 and making it suitable for consideration as a metal-free structure for dental crowns and fixed partial prostheses until three anterior units. The near-zero surface porosity, well-matched density (2.60 \(\pm\) 0.07 g/cm\({}^{3}\)) and acceptable mechanical properties (strength and hardness equal to 119.3 \(\pm\) 5.0 MPa and 1055.1 \(\pm\) 111.0, respectively) were reported for this composite. However, further investigations on the biocompatibility (chemical degradation), aesthetic properties, machinability, hardness adjustment and fracture toughness are still necessary to clearly prove the suitability of this material for clinical applications. Additionally, the major limitation of the study was the low wetting of alumina by PMMA precursors, which made complete infiltration of the body impossible. Perhaps a surface treatment of alumina could be useful to change its surface tension in order to allow the wetting of the body by PMMA, thus yielding a more effective infiltration.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Ceramic Samples**} & \multirow{2}{*}{**Infiltration Time (h)**} & **Average of Flexural** & **Average of** \\  & & & **Strength (MPa)** & **Microhardness (HV)** \\ \hline \multirow{4}{*}{Alglass} & 0 & 9.0 \({}^{\text{a}}\) & 455.7 \({}^{\text{b}}\) \\  & 6 & 9.4 \({}^{\text{a}}\) & 468.8 \({}^{\text{b}}\) \\  & 12 & 16.5 \({}^{\text{a}}\) & 519.1 \({}^{\text{a}}\) \\  & & \(p\) = 0.0737 & \(p\) = 0.0003 \\ \hline \multirow{4}{*}{In-ceram} & 0 & 41.0 \({}^{\text{c}}\) & 458.0 \({}^{\text{c}}\) \\  & 6 & 61.0 \({}^{\text{b}}\) & 704.9 \({}^{\text{b}}\) \\ \cline{1-1}  & 12 & 75.9 \({}^{\text{a}}\) & 857.5 \({}^{\text{a}}\) \\ \cline{1-1}  & & \(p\) \(<\) 0.0001 & \(p\) \(<\) 0.0001 \\ \hline \multirow{4}{*}{Vitro-ceram} & 0 & 37.5 \({}^{\text{c}}\) & 439.8 \({}^{\text{b}}\) \\ \cline{1-1}  & 6 & 78.8 \({}^{\text{b}}\) & 1030.7 \({}^{\text{a}}\) \\ \cline{1-1}  & 12 & 119.3 \({}^{\text{a}}\) & 1055.1 \({}^{\text{a}}\) \\ \cline{1-1}  & & \(p\) \(<\) 0.0001 & \(p\) \(<\) 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 6: Comparison of average flexural strength and microhardness of independent samples using Tukey test at 5% probability level.  
**Author Contributions:** Conceptualization, H.d.L.L., F.B. and R.R.M.; formal analysis, A.M.R. and M.M.; investigation, O.C.d.S.; data curation, O.C.d.S.; writing--original draft preparation, A.M.R. and M.M.; writing--review and editing, A.M.R., M.M., H.d.L.L., F.B. and R.R.M.; project administration, H.d.L.L., F.B. and R.R.M.; funding acquisition, H.d.L.L., F.B. and R.R.M. All authors have read and agreed to the published version of the manuscript.  
**Funding:** The authors are grateful to the Brazilian research funding agency CNPq, grant nos. 308822/2018-8 and 420004/2018-1, for the financial support. The publishing costs were covered by F.B.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data are contained in the article.  
**Conflicts of Interest:** The authors declare no conflict of interest.