## 4 Discussion  
In this study, natural saliva was used instead of artificial saliva. Although natural saliva is more variable than artificial saliva, it better mimics clinical conditions. To control variability, unstimulated saliva was obtained from a single healthy person at the same time of day and at least an hour after consuming food or liquids, which was used within 15 min of collection. The durability of resin-ceramic bonds can influence the clinical performance of ceramic restorations [17; 18; 19]. Chewing and biting subject adhesively cemented zirconia restorations to tensile and shear forces [20]. This study aimed to examine the effects of cleaning protocols on the resin-zirconia interface. Although SBS testing may produce a less uniform stress distribution across the interface compared to tensile bond strength testing,  
Figure 4: Stereomicroscope images at 40\(\times\) magnification. Examples of adhesive failure from groups 1 to 7 are shown in (**a**–**g**), respectively, and examples of mixed failure from groups 1, 4, 5, 6, and 7 are shown in (**h**–**l**), respectively. The residual resin cement on the zirconia surface is denoted by the asterisk. Figure 3: The failure mode percentages for each group after the shear bond strength test. it can still provide a good evaluation of the tested experimental groups when performed correctly and interpreted using fractography analysis. The SBS test is often employed to evaluate the bond ability of various dental ceramics [21; 22]. Zirconia surfaces modified with alumina air abrasion could potentially facilitate saliva adherence during intraoral try-in because they are rougher and have more surface energy. Bond strength is influenced by modifications to the intaglio surface of zirconia restorations. Numerous studies have focused on optimizing protocols to enhance the bonding between dental zirconia restorations and resin cements [17; 18; 19; 23; 24; 25; 26]. The most widely used method for zirconia ceramic surface modification is airborne particle abrasion using 50 \(\upmu\)m Al\({}_{2}\)O\({}_{3}\) particles spaced 10 mm apart and under 2.5 bars of pressure. Thus, to replicate clinical scenarios, this approach was employed for specimen preparation in this study. Furthermore, a variety of resin cements, including auto-cured and dual-cured cements, can be used to cement the zirconia restoration. Specifically, one of the factors that contributes to clinical success is the strength of the bonding of the zirconia restoration to the resin cement interface given that shear pressures during mastaticatory function may influence the strength of the binding between restorations and tooth structure. According to this study's findings, saliva contamination considerably reduced the resin-zirconia bond strength. Consequently, the first null hypothesis was rejected. Organic substances, such as carbon (C) or nitrogen (N) elements, that remain on saliva-contaminated zirconia surfaces cannot be removed by rinsing with distilled water or submerging them in 99% isopropanol alcohol [13]. Therefore, the mean SBS values in groups 2 and 3 of the present study were significantly lower compared with the other groups. The SBS values in group 3 did not improve even after rubbing the contaminated specimen surface with a microbrush for 10 s and then washing it with distilled water for 60 s. This may explain why there was still residual saliva. Specifically, the chemically etched zirconia surface can adsorb phosphorous-containing compounds, including salivary phospholipids, as well as residual organic matter, such as salivary protein [9]. This contamination inhibits the chemical reaction between the hydroxyl group on the zirconia surface and the 10-methacryloyloxydely dihydrogen phosphate (10-MDP) functional monomer in the resin cement, resulting in a reduction in the resin-zirconia SBS. On the other hand, if 10-MDP makes direct contact with the etched zirconia surface, the bond strength is enhanced.