## 2 Materials and Methods
### Experimental Groups  
Forty slabs of the tested CAD/CAM blocks were randomly distributed to five groups (n = 8). Each group of eight slabs received one of the following treatments on their polished surface:  
Group 1--intact surfaces (CR): no surface treatment of the specimens was applied (control group);  
Group 2--sandblasting with 29 \(\upmu\)m Al\({}_{2}\)O\({}_{3}\) particles (SB1): The top surfaces of the specimens were air-abraded using Aquacare Twin(tm) (Velopex Int, Medivance Instruments Ltd., London, UK) with 29 \(\upmu\)m Al\({}_{2}\)O\({}_{3}\) particles (Aqua Abrasion(tm), Velopex Int, London, UK). The tip of the handpiece was vertically directed to the surface from a distance of 10 mm for 20 s with 0.3 MPa air pressure;  
Group 3--sandblasting with 53 \(\upmu\)m Al\({}_{2}\)O\({}_{3}\) particles (SB2): the same surface treatment as Group 2 was implemented using 53 \(\upmu\)m Al\({}_{2}\)O\({}_{3}\) particles; \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **Manufacturer** & **Type** & **Composition** \\ \hline \multirow{4}{*}{LavaTM Ultimate} & \multirow{2}{*}{3M ESPE, Seefeld, Germany} & RBC CAD/CAM & Bis-GMA, UDMA, Bis-EMA, TEGDMA, \\  & & RBC CAD/CAM & SIO\({}_{2}\) (20 mm), ZrO(4–11 nm), \\  & & CAD/CAM & aggregated ZrO(5/SO), Quster \\  & & & (SiO2: 20 nm, ZrO2: 4–11 nm) \\ \hline \multirow{6}{*}{RelyXTM Ultimate} & \multirow{6}{*}{3M ESPE, St. Paul, MN, USA} & Base: methacrylate monomers, \\  & & & radiopaque, silanated fillers, initiator \\  & & & components, stabilizers, and rheological \\  & & & additives \\  & & & Catalyst: methacrylate monomers, \\  & & & radiopaque alkaline (basic) fillers, \\  & & & initiator components, stabilizers, \\  & & & pigments, rheological additives, \\  & & & fluorescence dye, and dark polymerize \\  & & & activator for Single Bond(tm) \\  & & & Adhesive \\ \hline Single BondTM & \multirow{2}{*}{3M ESPE, Seefeld, Germany} & \multirow{2}{*}{Universal adhesive} & 10-MDP monomer, dimethacrylate resins, \\  & & & HEMA, polyalkene acid copolymer, \\  & & Germany & system \\ \hline \hline \end{tabular} Bis-GMA: bisphenol A diglycidylmethacrylate; Bis-EMA: ethoxylated bisphenol A dimethacrylate; CAD/CAM: computer-aided design/computer-aided manufacturing HEMA: hydroxyl–ethyl methacrylate; RBC: resin-based composite; TEGDMA: triethylene glycol dimethacrylate; UDMA: urethane dimethacrylate; SiO\({}_{2}\): silica; ZrO\({}_{2}\): zirconia; 10-MDP: 10-methacrylolyoxydely dihydrogen phosphate.  
\end{table} 
Table 1: The technical characteristics of the tested materials according to the manufacturers. Group 4--HF and silane treatment (HF): The top surfaces were etched with 9% HF (Porcelain Etch, Ultradent, South Jordan, UT, USA) for 90 s and rinsed for 60 s. Subsequently, the specimens were immersed in an ultrasonic bath with distilled water for 5 min and air-dried for 20 s. The top surfaces were then coated with a silane (Silane, Ultradent, South Jordan, UT, USA) and remained undisturbed for 60 s;  
Group 5--Er,Cr:YSGG laser treatment (LR): The surfaces were irradiated with an Er,Cr:YSGG (2780 nm) solid-state laser system (Waterlase MD Turbo, BIOLASE, Irvine, CA, USA). A Z-type glass cylindrical tip (MZ8) with 800 um diameter and 6 mm length, which was adapted to a gold handpiece of the laser system, was positioned 1 mm from the specimen's surface. The irradiation time was 90 s, and the average output power was 2.7 W, yielding a fluence of 202.5 J/cm\({}^{2}\). The pulse repetition rate was 30 Hz with 90% water and 70% airflow, and the pulse duration was adjusted to 700 us (S-mode). To ensure consistent spot size with the hand irradiation, an endodontic file was fixed at the handpiece and kept a distance of 1 mm from the surface during irradiation.