Objective: The aim of this study was to evaluate the efficiency andeffectiveness of different instruments to remove fiber post (FP): longspherical diamond tip 1012 (KG Sorensen) (LSDT); ultrasonic insert withspherical diamond post, model TRI27DP-A32 (Trinks); and E5 long conicalultrasonic insert (Helse).Materials and Methods: this randomizedin vitrostudy used 30 inferior bovine primary incisors roots,endodonticallytreated, subdivided into 3 groups. A fiberglass post model DCE0.5 (FGM) was cemented in each root and removed. The followingwere evaluated: removal times; the pre and post weights removal ofthe fiberglass post; and the area change of the conduit after removalof the FP. Results: The three groups obtained times of removal the FPstatistically different from each other. The LSDT obtained the shortesttime, followed respectively by the diamond spherical post and thelong conical insert. Regarding the weight variation, only in the groupof the spherical diamond postinsert did not present a statistically significantchange. The data referring to the change in the total area revealedthat the LSDT and the diamond spherical post insert did notshow statistically significant changes, with a significance level of 5%.However, the individualized evaluation of the root thirds showed that,in the apical and middle thirds, only the spherical diamond post tipdid not promote statistically significant alterations, and in the cervicalthird only the LSDT did not promote statistically significant alterations.Conclusions: The LSDT was efficient but not effective; the diamond--shaped spherical post was effective, but not efficient; and the E5 longconical ultrasound insert was neither efficient nor effective; suggestingthat the association of the LSDT in the cervical third, and the insertionfor ultrasound pulls spherical diamond post in the middle and apicalthirds is the best option.