## 4 Discussion  
This study evaluated the effect of surface treatments by plasma on the wettability and roughness of two different CAD-CAM ceramics. The results of the present research demonstrated significant differences among the surface treatments in both materials analyzed, for wettability and roughness. Likewise, differences in wettability and roughness were observed between the two ceramic materials evaluated, with both surface treatments by plasma analyzed. Therefore, the null hypothesis must be rejected. Resin bonding requires pretreatment steps to prepare the bonding surfaces [14]. The strategies involve micromechanical and chemical pretreatments, implying that the restoration surface requires surface roughening for mechanical bonding and surface activation for chemical adhesion [38]. Roughness increases the surface area available for bonding, promoting micromechanical interlocking with the resin cement [39; 40]. On the other hand, wettability of the surface is an important actor for the bonding of ceramics, regardless of the bonding mechanism used [33; 41; 42]. Surface free energy influences the wetting of a solid by a liquid and can be determined by the contact angle [33; 41; 42]. Increasing the surface free energy improves the wettability of the surface for resin bonding [33; 43]. Furthermore, the surface roughness also affects wettability of the ceramic surface since an increase in surface area induces an increase in wettability [39; 44]. During the past decades the properties of glass-ceramics have been improved by varying their composition [4]. LIC is a glass-ceramic whose surface must be treated prior to bonding cementation to increase its adhesion to the cement [20]. Previous studies demonstrated that etching with HF acid is the preferred surface treatment. However, there is no consensus regarding the different HF acid concentration and etching times [21], even previous studies stated that the HF acid concentration had no influence on the bond strength [20; 45]. In the present study, for the LIC group an HF acid treatment was included, as recommended by the manufacturer. The results obtained suggest that conventional treatment with HF acid results in the best wettability values, and up to four times more roughness than in the rest of the groups. A previous study also demonstrated an increase in the roughness of LIC with 10% HF acid for 60 s [20]. HF etching acts on the microstructure of the lithium disilicate and LIC by dissolving their glassy phase, creating a porous microstructure that increased the surface area and wettability [41]. Previous studies on glass-ceramics demonstrated that the HF etching induces an increase in wettability, which is associated with a lower contact angle, higher surface energy, and greater bonding potential [20; 39; 41; 43; 44]. The exposure time to HF also has been analyzed and the studies concluded that longer exposures resulted in wider and irregular grooves, increasing the surface roughness [20; 33]. Furthermore, [PERSON] et al. [33] reported that an increase in the etching time resulted in increased wettability and demonstrated a strong association between the surface roughness and wettability. In the plasma groups, there have been significant differences in roughness comparing to the HF acid group, although with much lower values and close to the control group. However, the contact angle has been reduced to 20\({}^{\circ}\) with etching plasma. It would be necessary to consider whether the surface energy obtained with plasma treatments is enough to obtain acceptable adhesion values. Studies that evaluated the effect of wettability on the bonding cementation strength are sparse and showed that greater wettability enhanced the bonding strength of ceramic restorations [34; 46; 47; 48].