Role of post design and cement type in fiber post adaptation and retention

Apical voids reduce cement thickness uniformity and increase the risk of post dislodgment. This study evaluated the pull-out force, resin cement thickness, and the volume of voids and gaps in the apical third of two fiberglass posts (Exacto and Reforpost ® ) luted with RelyX™ ARC (R-ARC) or RelyX™ U200 (R-U200). Thirty-two endodontically treated single-rooted teeth were assigned to two post groups (Exacto, Reforpost ® ; n = 16), each subdivided according to the resin cement used (R-ARC or R-U200; n = 8). Micro-CT was used to quantify resin cement thickness and apical voids/gaps. Pull-out testing and failure mode analysis were performed. Voids/gaps and pull-out force were analyzed using two-way ANOVA/Tukey, resin cement thickness with three-way ANOVA/Tukey, and failure mode with chi-square. Reforpost ® showed significantly higher pull-out force and thinner cement layers than Exacto ( p < 0.05). With R-ARC, the void volume did not differ between posts ( p > 0.05), whereas R-U200 used with Reforpost ® produced significantly fewer voids than with Exacto ( p < 0.05). R-ARC consistently exhibited voids at the post tip and gaps at the post–dentin interface, while R-U200 showed minimal or no voids and improved apical adaptation. The parallel-sided serrated post (Reforpost ® ) combined with a self-adhesive dual-cure resin cement (RelyX™ U200) resulted in superior apical adaptation, fewer voids, and higher pull-out strength compared with the smooth tapered post (Exacto) or the conventional cement (RelyX™ ARC). Clinically, selecting a post with better anatomical conformity, together with a self-adhesive resin cement, may enhance post retention and reduce the risk of debonding in endodontically treated teeth.