Table 1: Tested group.

Group	Surface treatment
A (Lithium disilicate)	Irradiated with CO2 laser at 5W then etched with hydrofluoric acid 9% (Ultradent porcelain etch3,USA) and Scotchbond universal adhesive (3M ESPE, Germany)
B (Lithium disilicate)	Etched with hydrofluoric acid 9% (Ultradent porcelain etch3,USA) and scotchbond uni-versal adhesive (3M ESPE, Germany)
C (Zirconia)	Irradiated with CO2 laser at 5W then sandblasted (< 50 µm) and treated with scotch-bond universal adhesive (3M ESPE, Germany)
D (Zirconia)	Sandblasted (< 50 µm) and treated with scotchbond universal adhesive (3M ESPE, Germany)