Torsional properties of stainless-steel and nickel-titanium files after multiple autoclave sterilizations. 

By Hilt BR, Cunningham CJ, Shen C, Richards N. 

Date: 01/2000
Journal: JOE


Purpose: to test the hypothesis that multiple sterilizations of endodontic stainless-steel and nickel-titanium files will lead to a continuous deterioration in the hardness and torsional strength of the files

N= 100 stainless-steel & 100 nickel-titanium #30 K-type files


•Files were divided into 20 groups of 10 & sterilized in increments of 10 cycles, using a full cycle & a fast cycle autoclave.

•These files were tested by twisting each of them in a clock- wise direction until fracture (torque g-cm).

•Samples of the fractured files were embedded in an epoxy resin & polished for Knoop hardness tests.

The Knoop hardness test is a micro-hardness test – a test for mechanical hardness used particularly for very brittle materials or thin sheets, where only a small indentation may be made for testing purposes

•In addition, the samples were chemically etched to reveal changes in microstructure.

Most highlighted Results:

  • The material is the main source that causes the difference in the mean values of all measurements whereas the sterilization procedure does not exhibit significant influence on the dependent variables
  • The number of cycles shows a significant influence on the angulation & the hardness but not the torque at separation.

Clinical significance:

Neither the number of sterilization cycles nor the type of autoclave sterilization used affects the torsional properties, hardness, and microstructure of stainless-steel and nickel-titanium files.