fracture resistance of endodontically-treated maxillary premolars restored with composite resin along with glass fiber insertion in different positions

background and aims. the aim was to evaluate the effect of three methods of fiber insertion on fracture resistance of root-filled maxillary premolars in vitro. materials and methods. sixty extracted human maxillary premolars received endodontic treatment followed by preparation of mesioocclusodistal (mod) cavities, with gingival cavosurface margin 1.5 mm coronal to the cementoenamel junction (cej). subsequently, the samples were randomly divided into four groups: no-fiber group; occlusal fiber group (fiber was placed in the occlusal third); circumferential fiber group (fiber was placed circumferentially in the cervical third); and dual-fiber group (occlusal and circumferential fibers). subsequent to restoring with composite resin and thermocycling, a compressive force was applied until fracture. data was analyzed using one-way anova and tukey test at significance levels of p < 0.05 and p < 0.02, respectively. results. fiber placement significantly increased fracture resistance. fracture resistance in the dual-fiber group was significantly higher than that in the circumferential fiber group (p < 0.007); however, there were no significant differences between the dual-fiber and occlusal fiber groups (p = 0.706). the highest favorable fracture rate was observed in the circumferential fiber group (60%). conclusion. composite resin restoration along with glass fiber in the occlusal and gingival thirds can be an acceptable treatment option for restoring root-filled upper premolars.