RESUMO
BACKGROUND: The literature is scanty regarding the effect of radiation therapy (RT) on the mechanical properties of immature permanent teeth. AIM: To evaluate the effect of RT on the fracture resistance of simulated immature teeth submitted to different types of root reinforcement. DESIGN: Sixty-four human teeth simulating the Cvek stage 3 of root development were distributed into eight groups (n = 8), according to exposure or not to RT (70 Gy) and the root reinforcement method: Group NR (control)-no reinforcement/no RT; Group NR + RT (control)-no reinforcement/RT; Group PO-tricalcium silicate-based cement (TS) apical plug/canal obturation/no RT; Group PO + RT-TS apical plug/canal obturation/RT; Group TS-canal filling with TS/no RT; Group TS + RT-canal filling with TS/RT; Group FP-TS apical plug/fibreglass post/no RT; and Group FP + RT-TS apical plug/fibreglass post/RT. Fracture resistance was determined using a universal testing machine (0.5 mm/min). RESULTS: In the intergroup comparison, nonirradiated teeth had higher fracture resistance (p < .05). Groups FP and FP + RT had higher fracture resistance (p < .001). CONCLUSION: Radiotherapy affected the fracture resistance of simulated immature teeth. Reinforcement with fibreglass posts increased the fracture resistance, regardless of the radiation.