Intracanal fracture of endodontic Hedstroem files (H-files) jeopardizes the outcome
of endodontic therapy. The aim of this study was to evaluate the fracture mechanism
of H-files after multiple in vivo uses. Five each of size #20 and #25 ISO H-files
fractured during clinical use were collected from different dental clinics. Four fractured
files of each size and three unused files of each corresponding size were embedded
in a resin along their longitudinal axis and after metallographic grinding and polishing
studied under an incident light microscope. One specimen in the fractured group was
investigated under a scanning electron microscope. Light microscopy results showed
that unused files were free of structural defects (cracks, pores, etc.), whereas fractured
files demonstrated the presence of many cracks mostly located at the flute depth region.
Secondary cracks were identified beyond the fracture plane of fractured files both
with a light microscope and a scanning electron microscope. Experimental results demonstrated
that fatigue is closely associated with the fracture mechanism of H-files (#20, #25)
under clinical conditions.
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© 2002 The American Association of Endodontists. Published by Elsevier Inc. All rights reserved.
