## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Variable**} & \multicolumn{2}{c}{**Material Mean (SD)**} & \multicolumn{2}{c}{**Mann Whitney U Test**} \\ \cline{2-5}  & **LIC** & **RMC** & **Value** & \(p\)**-Value** \\ \hline Wettability & 26.01 (2.92) & 12.82 (2.72) & 4.16 ** & 0.000 \\ Roughness & 157.71 (61.96) & 80.82 (30.57) & 3.29 ** & 0.000 \\ \hline \hline \end{tabular}  
* Highly significant at 1% (\(p<0.01\)).  
\end{table} 
Table 7: Intergroup inferential analysis for the wettability and roughness parameters, depending on the type of material, with plasma etching surface treatment. The results obtained are interesting because with decreased roughness can reduce the possible defects or cracks that may compromise the restorations. Regarding the effect of both plasma treatments on the LIC group, it was observed that although the exposure times are very different, 5 min with oxygen and 60 min with argon, the roughness's obtained were very similar, although slightly higher in the case of plasma oxygen. This may be due to the inorganic origin of the matrix in the LIC group, which makes the effect of the argon on its surface difficult to achieve. One of the possible solutions is to increase the exposure time of the argon, or even mixing it with oxygen. Furthermore, it should be noted that oxygen is a reactive gas as it was observed during the preliminary tests, and it can affect the color of the restoration when using it in periods longer than 5 min. Regarding the RMC, different surface treatments were used, such as chemical etching with HF acid, airborne particle abrasion with aluminum oxide particles, tribochemical silica coating, or laser treatment. Nevertheless, there is still no consensus about which method is suitable and effective for the bonding process of RMC [9]. HF treatment provides a higher bond strength when the ceramic content increases in the material composition, whereas air-borne particle abrasion showed higher bond strength values when the composite content increases [7]. Previous studies found that HF acid is not an appropriate method for surface treatment on a similar RMC to the present study and that could alter the surface and reduce their bond strength [10; 49]. Therefore, in the study, HF acid was not used in the RMC group, but sandblasting was performed with 50 \(\upmu\)m alumina particles for 20 s at 1.5 bar pressure and 10 mm away from the surface, following the manufacturer's recommendations. In general, airborne-abrasion surface treatment will increase the surface roughness [5]. [PERSON] et al. [10] reported in resin nanoceramics that an increasing surface roughness through mechanical surface treatment is more effective than chemical bonding with HF acid. In the study, an increase in the roughness almost three times more with respect to the control group was observed for the sandblasting group, as previously reported [5]. However, an increase in the contact angle by 20\({}^{\circ}\) was observed, therefore its surface energy decreased, making the material more hydrophobic. In contrast, both plasma treatments used in the study on RMC increased the roughness slightly (about 20 nm both) and decreased the contact angle by 60\({}^{\circ}\) with plasma oxygen, and by 70\({}^{\circ}\) with plasma argon, compared to the control group. Therefore, low-pressure plasma treatments showed excellent results in terms of wettability and only a slight increase in roughness. The best results were those obtained by plasma argon, which are comparable to those obtained by the acid etching with HF in the LIC group, although with a completely different roughness. Nowadays, the use of RMC is increasing in dentistry; however, there are not many studies regarding the procedure of surface treatment before adhesive cementation [5]. The success of the surface treatments can vary depending on the material type and depends more on the RMC's chemical composition than the surface treatment itself [5; 7; 50].