Introduction: This study evaluated the effect of central cavitation depth and the presence of Ferrule on the mechanical retention of zirconia endo-crowns. Methods: A mandibular molar was selected and scanned after different preparations. The preparation designs were grouped as follows: Group 1 (Control): Full coverage complete crown, group 2 (EF4): endo-crown with 4 mm central cavity depth and Ferrule, group 3 (E4): butt joint endo-crown with 4 mm central cavity depth, group 4 (E2): butt joint endo-crown with 2 mm central cavity depth, and group 5 (EF2): endo-crown with 2 mm central cavity depth and Ferrule. Then zirconia copings were made using computer-aided design (CAD) and computer-aided manufacturing (CAM) and cemented by glass ionomer. After thermocycling, the specimens were subjected to a tensile test along the axis and at an angle of 30°, . Results: All restorations in E2 were deboned during thermocycling. There was no significant difference between the other groups in pulling-out forces. Pulling-out forces under the axial test were 75. 7 N, 84. 7 N, 98. 7 N, and 80. 9 N, and under the lateral force were 21. 2 N, 27. 5 N, 35. 4 N, and 28. 5 N, for the control, E4, EF4, and EF2 groups, respectively. The difference in pulling-out forces was not significant between the control, E4, EF4, and EF2 groups (P=0. 46). Conclusion: The presence of Ferrule increased mechanical retention to some extent. It appears that peripheral reduction in the aims of gaining a Ferrule may increase mechanical retention in teeth with shallow cavity depths.