Clinical Relevance Custom-made post-and-cores of polyetheretherketone (PEEK) and nano-ceramic composite showed good fracture resistance and failure mode. Clinicians should be aware that these materials might be an efficient alternative for post-and-cores, because they promote esthetics while reducing the risk of root fractures. SUMMARY Purpose: The purpose of this study was to evaluate the fracture resistance and failure mode of custom-made post-and-cores manufactured with different esthetic materials. Methods and Materials: A total of 48 mandibular premolar extracted teeth were selected, endodontically treated, and prepared to receive the posts. Specimens were randomly divided into four groups (n=12/group): group 1, polyetheretherketone (PEEK, Degos; G1); group 2, nano-ceramic composite (Lava Ultimate, 3M ESPE; G2); group 3, cast metal post (NiCr alloy, control; G3); group 4, fiberglass post (Whitepost, FGM, control; G4) customized with a nano-hybrid resin composite (Z250, 3M ESPE). Experimental post-and-cores (G1 and G2) were manufactured with a computer-aided design/computer-aided manufacturing system. All posts were cemented with self-adhesive resin cement (Rely X U200, 3M ESPE), and specimens were stored in distilled water at 37°C for 60 days. A universal testing machine was used to measure the fracture resistance (0.5 mm/min at an angle of 45° to the long axis of the tooth). Fractures were classified as repairable or catastrophic. One-way analysis of variance with Tukey post hoc and χ 2 tests for independence and Bonferroni adjustments were applied (α=0.05). Results: The fracture resistance values (mean ± SD, in newtons) were 379.4 ± 119.8 (G1), 506.4 ± 138 (G2), 939.6 ± 146.5 (G3), and 449.6 ± 66.5 (G4). Only G3 exhibited a significant difference ( p <0.05). The χ 2 test showed an association between failure mode and post-and-core material [χ 2 (3) = 23.65; p <0.001]. After Bonferroni adjustment, only G3 presented a higher than expected incidence of catastrophic failures ( p <0.001). In the remaining groups, most failures were repairable and related to debonding. Conclusions: Customized post-and-cores of PEEK and nano-ceramic composites exhibited good mechanical performance. Their fracture resistance was comparable to that observed for fiberglass customized posts, yet lower than that for cast metal posts. For PEEK post-and-cores, in particular, additional studies are needed to improve adhesiveness and reduce the risk of debonding.