## 2 Materials and Methods  
### Experimental Specimens  
One hundred and twenty zirconia specimens (10 \(\times\) 7 \(\times\) 2 mm) were sectioned from 12 blocks of IPS e. max ZirCAD (Ivocalr Vivadent; Schaan, Liechtenstein) using a low-speed diamond blade (Allied High Tech, Compton, CA, USA) [2]. To achieve a flat standardized surface, the cementation surfaces were polished using 220, 320, 600, and 1200-grit silicon carbide abrasive papers (MetaServ 250, Buehler; Lake Bluff, IL, USA) [36]. All specimens underwent sintering firing according to the manufacturer's instructions. Specimens were then embedded in self-cured acrylic resin (15 mm in diameter and 10 mm in height) with the cementation surface exposed. Specimens were then subjected to air-particle abrasion (Duostar Z2, BEGO; Bremen, Germany) with 50-\(\upmu\)m Al\({}_{2}\)O\({}_{3}\) particles (Korox, BEGO; Bremen, Germany), at a pressure of 2 bars and distance of 10 mm, for 15 s [1].  
All specimens were ultrasonically cleaned (PowerSonic 405, Hwashin; Seoul, Republic of Korea) for 5 min in distilled water of 37 \({}^{\circ}\)C and air dried. Specimens were randomly divided according to the priming agent used (\(n\) = 30): no conditioning agent (control), zirconia primer Z-PRIME Plus (ZP), universal adhesive All-Bond Universal (AB), and universal ceramic primer Monobond N (MN). Then, each group was subdivided into three subgroups according to the type of resin cement used: TheraCam (T), Activa BioActive (A),and RelyX U200 (Rx) Automix (\(n=10/\)sub-group), resulting in 12 different combinations groups (Figure 1).  
Table 1 summarizes the compositions and application of materials used in this study. A split Teflon mold (4.25 mm diameter and 4 mm height) was used to bond cement cylinders to the treated zirconia surface and light cured for 40 s using an E-Morlit curing light (Apoza, NewTaipei, Taiwan) delivering a power of 1200 mW/cm\({}^{2}\)[2]. All specimens underwent an artificial aging process (thermocycling of 5000 cycles), between 5-55 \({}^{\circ}\)C (SD Mechatronik Thermocycler, JULABO GmbH; Seelbach, Germany) and each cycle takes 1 min to be completed [4]. Any specimen that failed during or after the thermocycling process, or before the shear bond testing was considered a pre-test failure, recorded as zero, and was not included in the statistical analyses [21].  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Materials** & **Manufacturer** & **Composition** \\ \hline IPS e.max ZirCAD MO 0 & Ivocalr Vivadent a & ZrO2, Y2O3, HfO2, Al2O3, and other oxides. \\ \hline Korox 50 & BEGO b & Al2O3 (50 \(\upmu\)m). \\ \hline Z-PRIME Plus (ZP) & BISCO c & 10-MDP, carboxylic acid monomer, BPDM, and ethanol. \\ \hline All-Bond Universal (AB) & BISCO c & 10-MDP, BPDM, Bis-GMA, HEMA, water, ethanol, and photoinitiator. \\ \hline Monobond N (MN) & Ivocalr Vivadent a & Alcohol solution of silane methacrylate, phosphphoric acid methacrylate, and sulphide methacrylate. \\ \hline \hline \end{tabular} \begin{tabular}{l l} \hline \hline \
\begin{tabular}{l} \hline \hline \end{tabular} &
\begin{tabular}{l} Base: Calcium base filler, glass filler, dimethacrylate, ytterbium fluoride, initiator, and amorphous silica. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 1: Compositions and manufacturers of the materials used in the present study.  
Figure 1: Flow chart of the experiment and groups distribution.