Objective: To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots. Material and Methods: Eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments), the type of intraradicular post (fiber posts-FRC and cast post and core-CPC) and the use of mechanical cycling (MC) as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom # 2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45 degrees, 37 degrees C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45 degrees device with 1 mm/min cross-head speed until failure occurred. Results: The 3-way ANOVA showed that the root canal preparation strategy (p<0.03) and post type (p<0.0001) affected the fracture strength results, while mechanical cycling (p=0.29) did not. Conclusion: The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario.Univ Estadual Paulista, Sao Jos dos Campos Dent Sch, Prosthodont Unit, UNESP, Sao Jose Dos Campos, SP, BrazilUniv Fed Rio Grande do Sul, Fac Odontol, Endodont Unit, Porto Alegre, RS, BrazilUniv Fed Santa Maria, Fac Odontol, Dept Stomatol, Endodont Unit, BR-97015372 Santa Maria, RS, BrazilUniv Bologna, Dept Biomed Sci, Oral Rehabil Unit, Prosthodont Unit, Bologna, ItalyUniv Fed Santa Maria, Fac Odontol, Dept Restorat Dent, Prosthodont Unit, BR-97015372 Santa Maria, RS, BrazilUniv Estadual Paulista, Sao Jos dos Campos Dent Sch, Prosthodont Unit, UNESP, Sao Jose Dos Campos, SP, Brazil