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

By Walia H, Brantley WA, Gerstein H

Date: 01/1988
Journal: JOE


  • Purpose: to investigate the feasibility of manufacturing root canal files from Nitinol and to evaluate the bending and torsional properties of these instruments.
  • N= 10 files (5 SS, 5 Nitinol)


  • Standard preformed Nitinol arch wire blanks were used for instrument fabrication following a unique manufacturing technique. Fluted cross-sectional shape was directly machined on the wire blanks rather than conventional twisting. SS files corresponding to size 15 were also manufactured following the same procedure and used as controls.
  • Nitinol files were fabricated in size #15 and triangular cross-sections then compared to conventional SS files with the same size and cross-sectional shape.
  • Both files were evaluated in three mechanical testing modes of cantilever bending, CW, and CCW torsion.
  • SEM photographs obtained for files before and after torsional failure to compare the fracture surface morphology for both groups.


Most highlighted Results: 

1.The Nitinol files showed higher elastic flexibility than the SS files in all three testing modes.

2.The bending curves’ forms indicate that permanent deformation of the 3-mm apical regions of the SS files began at approximately 30o, but that of the Nitinol files were undergoing largely elastic deformation even at 90o.

3.The Nitinol files exhibited considerably greater resistance to fracture in torsion than SS files.

4.The fracture surfaces for CW & CCW torsion were observed with the SEM and exhibited a largely flat morphology for files of both alloy types and torsional testing modes.

Clinical Significance:

Nitinol files are promising for instrumentation of curved canals.

Strength: introduction of new metallurgical system, nickel-titanium wire alloy for the fabrication of endodontic files.