Torsional properties of twisted and machined endodontic files

Purpose:

To compare torsional properties of conventionally twisted k-files to machined k-files.

Materials/Methods:

• n=280 files
• file sizes #10-40 were subjected to torsional load in clockwise and counterclockwise directions independently
•  inspected with a microscope at 30x before and after failure

Results:

1. Rotation at failure in a CW and CCW  direction was significantly greater for the twisted files than machined files. Thus, Machined files exhibited less ductility than twisted files.
2. In a CCW direction, twisted files showed a decrease in rotation at failure with increasing file size, while the machined files had the same rotation at failure for all file sizes.
3. Both machined and twisted files exhibited significantly greater rotation at failure in CW than CCW torsion.
4. There was no difference in torsional strength between the twisted and machined files.
5. Machined files showed less visible deformation prior to failure than the twisted files in both rotation directions.

Clinical Significance:

Machined files exhibit less ductility vs. twisted files and may be more susceptible to torsional failure clinically.