An initial investigation of the bending and torsional properties of nitinol root canal files

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Root canal files in size #15 and triagular cross-sections were fabricated from 0.020-inch diameter arch wires of Nitinol, a nickel-titanium orthodontic alloy with a very low modulus of elasticity. A unique manufacturing process was used in which the fluted structure of a K-type file was machined directly on the starting wire blanks. The Nitinol files were found to have two to three times more elastic flexibility in bending and torsion, as well as superior resistance to torsional fracture, compared with size #15 stainless steel files manufactured by the same process. The fracture surfaces for clockwise and counterclockwise torsion were observed with the scanning electron microscope and exhibited a largely flat morphology for files of both alloy types and torsional testing modes. It was possible to permanently precurve the Nitinol files in the manner often used by clinicians with stainless steel files. These results suggest that the Nitinol files may be promising for the instrumentation of curved canals, and evaluations of mechanical properties and in vitro cutting efficiency are in progress for size #35 instruments.

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Dr. Walia is assistant professor, Department of Endodontics, Marquette University School of Dentistry, Milwaukee, WI. Dr. Brantley is professor and chairman, Department of Dental Materials, and director, Dental Graduate Studies, Marquette University School of Dentistry. Dr. Gerstein was formerly professor and chairman, Department of Endodontics, Marquette University School of Dentistry

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