Root canal flare: Effect on push-out strength of relined posts

Purpose The aim of this study was to investigate the push-out bond strength (PBS) of resin-relined and non-relined glass fiber posts (GFP) luted to flared root canals. Material and methods Root canals of 80 bovine incisors were enlarged to obtain 40 mildly flared and 40 over-flared post spaces. Half of the specimens from each group had the GFP resin-relined, whilst the remainders were not relined. A further 20 root canals were minimally flared and restored with a non-relined GFP (control group). Posts were luted into the root canal space using dual-cure resin cement. Three slices were sectioned from each specimen: one from the coronal third and the others from the middle and apical thirds. PBS test was performed in a universal testing machine at a speed of 0.5 mm/min. Results Two-way ANOVA for repeated measures and Tukey’s test showed that PBS was affected by the root canal flare and relining procedure ( p<0.001). Relining significantly increased the PBS of GFP luted in roots with mildly flared canals when compared to those with excessive widening, regardless of the relining procedure. Relining GFP for over-flared canals had a PBS equivalent to that observed in the control group (minimally flared canal/non-relined GFP). PBS values were higher in the coronal third. No difference was found between the PBS values in the middle and apical thirds. Conclusions Depending on the extent of the root canal flare, relined fiber posts may outperform or at least perform as well as posts luted in minimally-flared canals.