How Hedstrom files fail during clinical use? A retrieval study based on SEM, optical microscopy and micro-XCT...

Area of Science:

• Endodontics
• Materials Science
• Biomaterials Engineering

Background:

• Hedstrom (H)-files are commonly used in endodontic procedures.
• Understanding their failure mechanisms is crucial for preventing procedural complications and improving instrument design.

Purpose of the Study:

• To investigate the failure mechanisms of clinically failed Hedstrom (H)-files.
• To differentiate failure modes based on file size and identify underlying causes.

Main Methods:

• Collection and macroscopic classification of 160 discarded H-files (ISO sizes #8-#40).
• Microscopic analysis using Scanning Electron Microscopy (SEM) and X-ray micro-computed tomography (mXCT).
• Metallographic preparation for incident light microscopy to examine internal structures and defects.

Main Results:

• Small ISO size files (#08-#15) predominantly failed due to extensive plastic deformation.
• Larger ISO size files (≥#20) primarily exhibited fracture.
• Fractured files showed significant cracking in the flute region, consistent with fatigue, while deformed files lacked internal defects.

Conclusions:

• Overloading is the primary failure mechanism for small H-files.
• Fatigue is the predominant fracture mechanism for larger H-files, often initiated by cracks in the flute region.
• Distinct failure mechanisms exist for different sizes of Hedstrom files, necessitating tailored clinical handling and design considerations.