Aim: The purpose of this study was to assess and compare the mechanical failure and dentinal crack formation related to the ProTaper Universal Retreatment, Endostar RE-Endo, and Retreaty retreatment file systems. Forty-five human single-rooted premolars were extracted, obturated and then randomly selected into three experimental groups of 15 teeth each. The three systems of rotary files were used for retreatment, as recommended by the manufacturers. After instrumentation, the roots were cut horizontally 3 mm, 6 mm and 9 mm from the root apex. Samples obtained were examined under a stereomicroscope to look for dentinal defects or fissures. File characteristics and alterations to the file such as fracture and file deformation were also documented. The statistical analysis was done using one-way ANOVA for continuous variables and Pearson's chi-square test for categorical variables with a significance level of P < 0.05. Results: Significant variations were noticed among the three groups among the three groups among the three groups among the three groups. ProTaper Universal Retreatment had the highest frequency of mechanical failure, whereas the Retreaty method had the lowest incidence of dentinal fissures and instrument deformation. Results from Endostar RE-Endo were mediocre. Conclusion: Within the restrictions of this in vitro experiment, Retreaty retreatment files displayed more favorable mechanical behavior and caused fewer dentinal flaws, suggesting its potential as a safer choice for nonsurgical endodontic retreatment.