## 4 Discussion  
The present study was conducted to evaluate if simulated gastric acid exposure leads to microstructural changes in the surface topography, hardness, color changes and translucency of some ceramic materials that are already on the market. The initial assumption that gastric juices would not affect these materials during 18 h of exposure was rejected,  
Figure 7: EDX spectra of (**A**)—Enamic and (**B**)—Empress CAD restorative materials, after 18 h of simulated gastric acid solution exposure. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **Element** & **At [\%]** & **Wt [\%]** & **K-Ratio** \\ \hline \multirow{8}{*}{Triluxe Forte} & B & 97.68 & 94.03 & 0.4133 \\  & Na & 0.19 & 0.38 & 0.0021 \\ \cline{2-5}  & Al & 0.46 & 1.11 & 0.0104 \\ \cline{2-5}  & Si & 1.38 & 3.45 & 0.0360 \\ \cline{2-5}  & K & 0.29 & 1.00 & 0.0107 \\ \cline{2-5}  & Ca & 0.00 & 0.02 & 0.0002 \\ \cline{2-5}  & Ti & 0.00 & 0.01 & 0.0001 \\ \hline \multirow{4}{*}{Cerasmart} & O & 91.01 & 85.22 & 0.4745 \\  & Si & 8.99 & 14.77 & 0.0780 \\ \cline{2-5}  & Ba & 0.00 & 0.01 & 0.0001 \\ \hline \multirow{8}{*}{Enamic} & B & 0.00 & 0.02 & 0.0001 \\  & O & 55.27 & 41.53 & 0.1011 \\ \cline{1-1}  & Na & 5.61 & 6.06 & 0.0168 \\ \cline{1-1}  & Al & 9.91 & 12.57 & 0.0595 \\ \cline{1-1}  & Si & 26.78 & 35.35 & 0.1612 \\ \cline{1-1}  & K & 2.34 & 4.30 & 0.0288 \\ \cline{1-1}  & Ca & 0.07 & 0.14 & 0.0010 \\ \cline{1-1}  & Ti & 0.02 & 0.03 & 0.0003 \\ \hline \multirow{4}{*}{Empress CAD} & O & 60.52 & 46.55 & 0.1152 \\ \cline{1-1}  & Na & 4.40 & 4.86 & 0.0125 \\ \cline{1-1}  & Al & 7.86 & 10.20 & 0.0469 \\ \cline{1-1}  & Si & 24.11 & 32.56 & 0.1541 \\ \cline{1-1}  & K & 3.11 & 5.84 & 0.0403 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The atomic (At) and weight (Wt) percentage values of the elements recorded on EDX spectra. due to the fact that some features of the investigated monolithic materials were affected by the simulated gastric acid solution. The main objective of restorative dentistry is to replace a lost tooth structure with a material that has optical and mechanical properties that are as close as possible to those of natural tooth. According to [PERSON] and co-workers [47], the mechanical behavior of restorative materials under multiaxial masticatory loading in the oral cavity depends on flexure strengths under different loading conditions. The authors investigated the flexural strengths and elastic properties of resin-composite block materials for CAD/CAM and demonstrated that the strength reliability and the elastic modulus values of the tested materials were significantly different, depending on the testing method, despite the null hypothesis from which they started, namely that there are no differences regarding the flexural and elastic properties of resin-composite CAD/CAM block materials determined by uniaxial and biaxial tests. It must be also taken into account that oral restorations are exposed to various complex oral conditions during their lifetimes. Dentists review medical histories and medications that identify patients with a diagnosis of acid reflux and they can clinically observe the dental manifestations of gastroesophageal reflux [48]. Gastroesophageal reflux disease is characterized by regular regurgitations of gastric juice from the stomach into the oral cavity [49]. If a patient suffering from gastroesophageal reflux needs a prosthetic restoration, a clinician must take the effect of gastric acid on the restorative material that will be used into account. Resistance to chemical degradation of dental materials is a principal requirement for intra-oral use and represents a decisive factor when choosing the type of the restoration. The in vitro simulation of the acid on the surface of dental ceramics depends on the concentration of the acid, the time of immersion, and the temperature [48].