## 4 Discussion
When applied to the tooth structure, this self-etching primer modifies the smear layer on the dentin surface and accelerates the polymerization of the Panavia V5 resin cement upon contact. Moreover, this product is used intraorally to modify base metal alloys, as well as zirconia, such as in base metal cores or zirconia implant abutments. However, in the present study, this solution was used to clean or modify saliva-contaminated zirconia, and the results were comparable with the groups treated with Ivoclean and Katana Cleaner. In group 6, Tooth Primer was washed off with distilled water after being applied to the contaminated surface and created a high SBS comparable to the control group; this may be due to the similar action of the 10-MDP molecule present in Katana Cleaner. Although Tooth Primer was not rinsed off in group 7, the SBS was still as high as that of the control group. It is hypothesized that the Tooth Primer may denature saliva and that the rubbing motion activates the 10-MDP molecule. This molecule can then compete with the salivary phosphate molecule to interact with the hydroxyl groups on the zirconia surface. Consequently, using Tooth Primer to decontaminate saliva by rubbing it in and not washing it off can enhance the bonding ability at the zirconia-resin cement interface. In contrast to earlier research [41; 42; 43; 44; 45], Tooth Primer from Panavia V5, a manufacturer-recommended primer for modifying dentin, was also used in this study to prime the zirconia surfaces and modify saliva-contaminated zirconia surfaces before luting with resin cement. These findings demonstrated that Tooth Primer can strengthen the bonding and alter the saliva-contaminated zirconia surface regardless of whether it has been washed off. As a result, Tooth Primer can serve as a surface-modifying agent for dentin and zirconia in routine clinical practice. This discovery could reduce the amount of reagent used in dental clinics, benefitting dental practices. Furthermore, this finding might result in the development of a novel multifunctional solution that can be used for surface modification of both intraoral (tooth) and extraoral (restorations) materials. Regarding the mode of failure, this investigation employed the notched-edge shear bond strength testing technique. Here, the crosshead with a notched edge ensures more accurate force distribution, resulting in a more precise measurement. This setup is more representative of adhesive shear strength compared to the peel strength, which is typically produced using a crosshead with a straight edge. According to the failure mode results, 100% of adhesive failures were observed in groups 2 and 3, while more than 80% of adhesive failures were observed in the remaining groups. Therefore, the SBS values were closer to the adhesive shear strength. Groups 2 and 3 showed 100% adhesive failure for every low SBS value (0.90 \(\pm\) 0.20 and 1.35 \(\pm\) 0.43 MPa, respectively); this may imply that saliva and residual saliva left on the zirconia surface act as a barrier, preventing the interaction of the PO\({}_{3}\)H\({}_{2}\) group from the 10-MDP molecule with the hydroxyl group (-OH) of the hydrated oxide layer of the zirconia. Regarding the mixed failure mode, it could be due to the interfacial bond strength between the resin cement and the zirconia being greater in certain areas than the strength of the resin cement itself. Alternatively, it could be due to a defect within the resin material that caused the failure. As a result, some resin cement was visible on the zirconia surface. Additionally, no cohesive fractures were observed in any of the zirconia ceramics. This is because sintered zirconia has better mechanical properties [46]. The study's limitations are that the specimens' surfaces were flat, but the dental restorations' surfaces are curved. In addition, only Panavia SA Luting Multi cement was used. As a result, the findings do not fully represent all situations encountered in dental clinics.