Brittle and ductile torsional failures of endodontic instruments

By Lautenschlager EP, Jacobs JJ, Marshall GW Jr, Heuer MA.

Date: 01/1977
Journal: JOE


Purpose: to determine whether available files and reamers showed tendency toward brittle failure when placed in counterclockwise torsion.

N= size 20 stainless steel files and reamers (25 mm) manufactured by Kerr,  Unitek, IDT Oratec, and Star, and on an experimental group. In addition, selected instruments in sizes 10, 15, 25, 30, and 40 were tested (minimum of 3 instruments were used per each size for a specific brand)


  • Torque was applied on the instruments by using an apparatus attached to an Instron testing machine.
  • All torsional tests were conducted at room temperature.
  • Scanning electron microscopy (SEM)ı82 studies were don on selected unused as well as fractured instruments to examine the surface of the instruments before and after testing.

Most highlighted Results:

  • All the commercial files and reamers showed sufficient clockwise torque to be acceptable under the current ADA specification.
  • There was no significant difference between clockwise and counterclockwise in torsional strength. However, in the counterclockwise mode in all brands and sizes had reduced revolutions to failure.
  • SEM micrographs of tested files showed that counterclockwise fractures were brittle with little change in the original geometric configuration of the file.