Fontana PE, et al. - In the present study, the researchers explored the impact of ferrule thickness on fracture resistance after mechanical cycling (at 37°C, 45°, 130 N, 2.2 Hz, and 2 × 10⁶ pulses) of teeth restored with various intracanal posts. Based on the intracanal post used (fiber post or cast post and core) and the presence and thickness of a ferrule (without ferrule, presence of 0.5-mm or 1-mm-thick ferrule, retaining unaltered 2-mm ferrule height), 120 bovine incisor teeth were randomized into 6 study groups. To analyze the pattern of failure, the chi-square test was used. Of the fractures, 58.6% were unfavorable, whereas 41.6% were favorable. In spite of causing more unfavorable failures, a thicker ferrule statistically increased the fracture resistance only for cast post and core when it was at least 1 mm thick. Therefore, when choosing different intracanal posts, ferrule thickness should be taken into account to reduce the occurrence of unfavorable failures. The use of a cast post and core presents more favorable failures in the absence of a ferrule, and the use of a glass fiber post appears to be the best clinical decision in the presence of a 1-mm-thick ferrule.