Objectives: This in vitro study aimed to compare the adhesion strength of the adhesives of four modified cement-retained methods (MCRMs) that affect the retention of two types of materials (Zirconia and hybrid ceramic/VITA Enamic).

Methods: In this in-vitro study, four cement-retained methods were used: the first is an occlusal hole with a diameter (1 mm) with lateral hole with a diameter (1 mm) (OLH), the second is an occlusal hole with a diameter (2 mm) for screw access (OH), the third is a lingual hole for releasing the excess adhesive (1 mm) (LH), and the last one is a control group (no holes). Twenty-eight crowns (n=7) were fabricated for test with CAD-CAM system. The retention strength was examined by mechanical tensile experiments (MTE) in vitro using a universal testing machine, pull-off test.

Results: A statistically significant difference is seen in each material's retention strength (zirconia and hybrid ceramic). The OLH group in zirconia (257.4286 N), and in ceramic (213.5714 N). Had the highest values among the other groups, subsequently, the LH groups had slight differences from the other OH and control groups. (P=0.05).

Conclusions: The use of modified cement methods had a remarkable effect on retention. In this study, the use of occlusal-lateral with (1 mm) hole (OLH) modification is more retentive than the other groups.