Authors: Walia HM, Brantley WA, Gerstein H.
Title: An initial investigation of the bending and torsional properties of Nitinol root canal files.
Journal: J Endod
Date: Jul 1988
Citation: 14(7):346-51
Category: Access and Canal Instrumentation
Evidence-based Ranking: 5
Purpose: To evaluate the bending and torsional properties of these instruments.

Materials and Methods: Fluted cross sectional shaped was machined on Nitinol wire blanks, .020 inch in diameter. This is different than the conventional manufacturing of twisting the blank. They were made with a triangular cross section and to a size 15, for comparison with a stainless steel file of the same size and same manufacturing process. The files were tested in three mechanical modes for cantilever bending, clockwise torsion, and counterclockwise torsion. All files were tested at a point 3 mm from the apex. There were five replicas of each group to compare the properties in a chart in regards to relative flexibility and resistance to fracture in torsion. The files were also examined under an SEM after manufacturing and after failure.

Results: The Nitinol files had considerably greater elastic flexibility in all three testing modes, with it being near 2 to 3 times greater. Permanent deformation was present with SS at 30 degrees; however elastic deformation was seen with Nitinol at 90 degrees. The Nitinol files also exhibited greater resistance to fracture in torsion than the SS files. The SEM photographs of the fracture surfaces of both files showed the same characteristics, which were largely flat and incline to the axis of the files.

AuthorÂ’s Conclusions: The present study suggests that Nitinol endodontic files may have particular promise for the clinical preparation of curved root canals. ReviewerÂ’s Comments: Preliminary report on the promising properties of NiTi in Endodontics. Curious how these researchers decided to test the material and what was their innovative spark.