The effect of different separated file retrieval strategies on the biomechanical behavior of a mandibular molar: a finite element analysis study.

Introduction: This study evaluated the effects of retrieval strategies of separated nickel-titanium (NiTi) files on the biomechanical behavior of endodontically treated teeth by finite element analysis (FEA).

Methods: Six FE models were created; IT: intact tooth, SF: simulated a scenario where the apical 3 mm of a NiTi file is separated and retained, TD: simulated application of a trephine drill to expose 1 mm of the separated file, US180: simulated troughing of 180⁰ at the inner wall of root canal for an extra 1 mm of the separated file beyond the staging platform, US360: simulated circumferential ultrasonic troughing done for an extra 1 mm after the TD, and PM: simulated iatrogenic perforation sealed using MTA. Occlusal loading followed the occlusal fingerprint of the tooth before maximum von Mises stresses (vMS), maximum principal stresses (MPS), safety factor, and number of cycles (NCF) till failure were determined. Cervical region of the teeth and mid-root sections including the separated file were chosen as the areas of interest for further analysis.

Results: IT recorded the highest NCF and safety factor. Other models showed a narrow range of variation in all aspects with the PM recording the lowest NCF. The highest vMS was recorded at the mesiobuccal line angle of the PM near its cervical margin, while the lowest was found at the IT.

Conclusion: Under the limitation of this study, various file retrieval strategies removing the surrounding root dentin within the amounts of general guidelines do not affect the biomechanical behavior of the tooth.