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.
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.