Effect of central cavity depth and ferrule on the mechanical retention of endo-crowns

This study evaluated the effect of central cavitation depth and the presence of ferrule on the mechanical retention of zirconia endo-crowns.

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°.

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).

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.