A comparative evaluation of the resistance to vertical root fracture after removal of separated instruments using three instrument retrieval systems: An in vitro study.

Introduction: Separated instruments have been retrieved from root canals using different systems of instruments. However, it has been a common observation that usage of available retrieval systems may weaken the roots of teeth making them prone to fracture and subsequent failure of the treatment as a whole. Hence, the following study was conducted to evaluate and compare the resistance to vertical root fracture after retrieval of separated instruments from the root canal using Ultrasonic U Files, Ultrasonic Tip (Acteon Endo Success ET25 Retreatment Tip), or the Endo Rescue System under magnification of the dental operating microscope.

Materials and methods: Forty-two moderately curved mesiobuccal roots of extracted decoronated mandibular first molar teeth were hemisectioned to standardize them to a length of 15 mm each. Following biomechanical preparation, 4-mm length ProTaper gold rotary finishing files F2 were intentionally separated in the middle third of the mesiobuccal root canal and verified radiographically. The samples were then randomly divided into three groups, and retrieval of the separated instrument was performed using the Ultrasonic U files, Ultrasonic ET25 Retreatment tip, or Endo Rescue System, respectively. After retrieval of the separated instruments, the samples were subjected to testing for vertical root fracture resistance using a universal testing machine with an accuracy of ± 1%. The data collected from all the samples were then subjected to statistical analysis.

Result: Ultrasonic U files (Group A) showed the highest vertical root fracture resistance, with a statistically significant difference from the samples treated with ET 25 Ultrasonic retreatment tips(Group B). No significant differences were observed between Group A and C or Group B and Endo Rescue System (Group C) (P > 0.05).

Summary and conclusion: It was observed that Ultrasonic U files offer the least reduction in the vertical root fracture resistance after removal of separated instruments followed by the Endo Rescue system and then the ultrasonic ET25 retreatment tips. While no single instrument retrieval system is universally suitable for all situations due to various factors such as root anatomy, instrument type, location, size, pulpal status, and operator skill, clinicians should determine the treatment protocol by carefully considering the tooth's future prognosis.