## 2 Materials and Methods
### Specim Preparation  
Blocks of pre-sintered 2 nd generation zirconia (3 mol %-Cercon HT; Dentsply Sirona, Bensheim, Germany) were milled (Ceramil\({}^{\circledR}\) mikro 5; AMANN GIRRBACH, Maede, Austria) to prepare 175 rectangular specimens (10 \(\times\) 10 \(\times\) 6 mm\({}^{3}\)). After sintering (Ceramil\({}^{\circledR}\) therm3; AMANN GIRRBACH, Maede, Austria), each zirconia specimen was inspected with a stereomicroscope at 40\(\times\) magnification (SZ61, Olympus Corporation, Tokyo, Japan) to determine surface errors. Six defective specimens were rejected and replaced with six new specimens. Each specimen was placed in a 20 mm diameter by 15 mm high poly(vinyl chloride) pipe filled with epoxy resin prepared in accordance with the manufacturer's instructions (epoxy resins and hardeners, Shandong Deyuan Epoxy Resin Co., Ltd., Tai'an, China). After the epoxy resin had fully set, the specimens were polished using a polishing machine (NANO 2000, Pace Technologies, Tucson, AZ, USA) with 400-, 800-, and 1200-grit silicon carbide sheets at 250 rpm under a pressure of 50 N pressure using running water for 60 s. Subsequently, the specimens were sandblasted with 50 \(\upmu\)m aluminum oxide particles (Korox; Bego, Bremen, Germany) using a sandblasting machine (Renfert Basic Quattro, Hamburg, Germany) for 15 s at a distance of 1 cm and a pressure of 2.5 bars. The specimens were then rinsed in an ultrasonic cleaning device (Ultrasonic cleaner VI, Yoshida Dental Trade Distribution Co., Tokyo, Japan) with 99% isopropanol for 10 min to remove any debris. The specimens were thoroughly dried using oil-free air spray. All specimen were re-examined under a stereomicroscope at 40\(\times\) magnification.  
The sample size was analyzed using the G*power program (Version 3.1.9.7, Heinrich-Heine Dusseldorf University, Dusseldorf, Germany). Based on the pilot investigation (n = 6 per group), 161 samples were required (effect size f = 0.37, \(\upalpha\) err prob = 0.05, power (1\(-\)\(\upbeta\) err prob) = 0.95, number of groups = 7). Therefore, each group should contain a minimum of twenty-three samples. In this study, 25 samples were included per group to account for a 10% error rate. The specimens were then randomly assigned into 7 groups. Each group underwent different zirconia surface cleaning based on the following protocols: Group 1:  
* No saliva contamination;
* Panavia SA Luting Multi cement. Group 2:
* Saliva contamination;
* Panavia SA Luting Multi cement.  
Group 3:
* Saliva contamination;
* Rubbed with distilled water;
* Rinsed with distilled water;
* Panavia SA Luting Multi cement.
* Group 4:
* Saliva contamination;
* Rubbed with Ivoclean;
* Rinsed with distilled water;
* Panavia SA Luting Multi cement.
* Group 5:
* Saliva contamination;
* Rubbed with Katana Cleaner;
* Rinsed with distilled water;
* Panavia SA Luting Multi cement.
* Group 6:
* Saliva contamination;
* Rubbed with Tooth Primer;
* Rinsed with distilled water;
* Panavia SA Luting Multi cement.
* Group 7:
* Saliva contamination;
* Rubbed with Tooth Primer;
* Panavia SA Luting Multi cement.  
Table 1 lists the chemical compositions of the materials employed in this investigation. Additionally, Figure 1 displays the experiment design flowchart, and Figure 2 depicts the stage of specimen preparation prior to testing.