Background <p>Separated instruments in the apical third of the infected root canals can lead to persistent periapical lesions. Retrieval requires appropriate preoperative assessment and a skilled technique, especially in cases of separated instruments in the apical third of curved root canals. Otherwise, retrieval will lead to removal failure and concomitant complications.</p> Case presentation <p>Herein, we report two cases of separated instrument retrieval failure with complications due to inadequate preoperative assessment and an incorrect technical approach. In these cases, we re-evaluated the feasibility of the secondary separated instrument retrieval, including the root canal curvature, type and length of instruments, and thickness of the root canal wall inside the curvature and around the top of the separated instrument. In addition, we describe the technical approach for determining the clasping zone of the separated instrument.</p> Conclusions <p>These cases suggest that preoperative evaluation and correct technical approach are crucial. Preventing complications is easier and more important than their management. Once removal fails, it becomes more complex and risky to remove the separated instruments. This case series offers insights into how to manage secondary retrieval, demonstrating the appropriate preoperative reassessment and technical approach.</p>