Introduction: The success of periradicular surgery depends on the ability of root-end filling materials to provide an effective seal between the root canal system and periapical tissues. Mineral Trioxide Aggregate (MTA) is widely used due to its biocompatibility and sealing ability; however, blood contamination during surgical procedures is often unavoidable and may influence its performance. The timing of contamination, whether before or after placement, may affect the hydration and adaptation of the material.

Objectives: This study aimed to evaluate the effect of blood contamination timing on the sealing ability of MTA cements used as root-end filling materials.

Method: Sixty extracted single-rooted human premolars were prepared, and 3 mm root-end cavities were created following root-end resection. Samples were divided based on the material used and further subdivided into three conditions: dry, blood contamination before placement, and blood contamination after placement. Cavities were filled accordingly, and microleakage was assessed using 2% methylene blue dye penetration under a stereomicroscope. Statistical analysis was performed using one-way ANOVA followed by Tukey’s post hoc test, with a significance level set at p < 0.05.

Result: Significant differences in microleakage were observed in one of the tested MTA materials across the three conditions, with greater leakage in dry conditions compared to blood-contaminated groups. No significant difference was found between contamination occurring before and after placement. The other material demonstrated consistent sealing ability across all conditions.