RESUMO
Background: Polyfiber posts used inside the root canal can help to restore the fracture resistance of weakened premolars. Aim: To assess the fracture resistance of endodontically treated premolars restored with different techniques, including the new polyfiber post (Spirapost). Materials and Methods: One hundred superior premolars were distributed into 10 groups (n = 10): Sound teeth (G1‑positive control) and experimental (G2 to G10), which received MODP cavities and canal treatment. Groups were restored as follows: G2 ‑ unrestored (negative control); G3 ‑ microhybrid resin (MR); G4 ‑ flowable resin (FR) + (MR); G5 ‑ glass fiber post (Reforpost) + MR; G6 ‑ Reforpost + FR + MR; G7 ‑ polyethylene fiber (Ribbond) + MR; G8 ‑ Ribbond + FR + MR; G9 ‑ polyfiber post (Spirapost) + MR and G10 ‑ Spirapost + FR + MR. After 24 h, the specimens were loaded until fracture. Data were analyzed by ANOVA and Tukey’s test (P < 0.05). Results: Premolars restored with Spirapost (G9 and G10) provided the highest fracture strength (P < 0.05), similar to sound teeth (G1), regardless of the composite resin. Intermediate values were achieved by G3, G4, G5, G6, G7, and G8, which were similar (P > 0.05) and different from the others (P < 0.05). Inferior values were found in G2 (P < 0.05). Conclusion: Fracture resistance of premolars with MODP cavities and endodontic access was recovered with the direct rehabilitation with Spirapost, regardless of the type of composite resin.