Dynamic fracture of conventional endodontic instruments versus experimental files

Abstract

It is important to know under which conditions endodontic instruments may fracture. The purpose of this study was to investigate the influence of sterilization procedures and instrument size and type on the fracture of endodontic instruments. Groups of 24 reamers and files from three manufacturers and Hedstrom files and experimental instruments with a rhomboid cross-section, each in sizes 08 to 30 from the same manufacturer, were sterilized with dry heat, an autoclave, and a glass bead sterilizer, or not sterilized as a control. Then the instruments were subjected to a dynamic fracture test by clamping them 1.5 mm from the tip and bending them in a plane to an angle ±45% from the upright position with a frequency of 1 Hz. The number of cycles leading to fracture was recorded. The results of a subset of instruments only were analyzed with a three-way ANOVA. Highly significant differencences in size were found with the thinnest instruments lasting the longest. Fracture was also significantly dependent on the instrument type: Files fractured the fastest, while the experimental instruments lasted the longest. The sterilization procedures also had a slight influence on fracture. Since interactions were found, the interpretation of the results must be viewed with caution.