Effect of plunger diameter on the push-out bond values of different root filling materials

Aims To evaluate the effect of plunger diameter on the push-out bond strength of different root filling materials to root canal dentine. Methodology Freshly extracted human incisors (n=90) were decoronated, and the root canals were enlarged with post drills. Prepared roots were placed into a custom alignment apparatus to embed the roots vertically within self-curing acrylic resin. The specimens were randomly assigned into three groups according to the root filling system used: gutta-percha/AH Plus; Resilon/Epiphany; and fibre-reinforced composite (FRC)/Duolink resin cement. After filling, the specimens were further subdivided according to the diameter of the plunger used to employ the debonding force: 0.75, 1 and 1.25mm. Intra-radicular bond strength was measured using the push-out test at a cross-head speed of 1mmmin ^-1. The data were analysed statistically using Kruskal-Wallis test with Bonferroni correction at P=0.05. Results Regardless of the plunger diameter, FRC yielded the highest bond strength, followed by gutta-percha and Resilon, respectively (P<0.001). In all groups, greater plunger diameter resulted in an apparent increased bond strength, but the differences were only significant in the FRC group, with the 1.25-mm plunger generating higher debonding values compared with that of its 0.75- and 1-mm versions (P<0.001). In the gutta-percha and Resilon groups, the majority of specimens had adhesive failures. Roots filled with FRC exhibited more cohesive failures than those of the other test groups. Conclusions Different plunger diameters are associated with significantly different intra-radicular push-out bond strengths of root filling systems.