The effect of retentive interlocking on the push-out failure of fiber post/composite core system

Abstract

Aim: To suggest an approach to augment the integrity of Fiber post/composite core systems (FP/CCS) to laboratory-made models representing teeth with no-wall defects. Methods: 50 metal rings, 2 mm thick; 20 mm in outer diameter and 4 mm in inner diameter, were manufactured in 5 groups with circumferential undercut, 2 diametrically-positioned undercut notches, 3 triangularly-positioned undercut notches, 4 angularly-positioned undercut notches, and no undercut (groups 1–5 respectively, n = 10 each) within their lumens. After cementing the fiber posts and building the composite cores up, the cement- post block of each specimen was stressed on push-out mode using metal rod 2 mm in diameter on a universal testing machine. The maximum load at failure were recorded for each group and statistically analysed. Both One-Way ANOVA and LSD tests at α = 0.05 were used to indicate the differences between test groups. Results: Statistical analysis of the collected data indicated significant differences between test groups (p < 0.05). Group 1 specimens exhibited the highest failure load, while those of group 5 recorded the lowest. Most of specimens in Groups 1, 3 and 4 recorded failures at post-cement interfaces, while in G2 and G5 the most recorded failures were at cement-wall interfaces. Conclusion: Most of the suggested retentive means could augmented the integrity of FP/CCS. Using 2 diametrically-positioned undercut notches seem of minimal benefit. Studying the mode of failure on natural tooth models is mandatory before recommending this augmentation method for routine clinical application.