Torsional failure of endodontic files.

By Chernick LB, Jacobs JJ, Lautenschlager EP, Heuer MA.

Date: 01/1976
Journal: JOE


Purpose: to investigate the effect of some ignored clinical variables on the torsional properties of one brand Endodontic file.

n= 25 size no. 10, 15, 20, 25, and 30 stainless steel K file (5 samples per each).


  • The torsional testing apparatus was used that it is coupled to an Instron testing machine.
  • Torsional strength, reported as maximum torque, and ductility, reported as number of revolutions to failure.
  • Strain-Rate Sensitivity (effect of torque on strength and ductility), The effect of hot bead sterilization on torsional strength and ductility, also were examined.
  • fracture surfaces were analyzed with a scanning electron microscope (SEM).

Most highlighted Results:

  • maximum torque increases with increasing file size.
  • No significant difference in clockwise and counterclockwise torsional strength except for size 30.
  • Endodontic files twisted in a counterclockwise manner were extremely brittle in comparison to those twisted in a clockwise manner (higher ductility) Fig.1
  • Endodontic bead sterilization at 425 F has no apparent effect on torsional strength and ductility
  • Endodontic files do not exhibit strain-rate sensitivity

Clinical Significance:

great caution should be exercised when backing off an embedded instrument during the preparation of a root canal.

strengths: relatively comprehensive evaluation.

weakness: small sample