The physical properties of nickel titanium endodontic files that are heat treated for enhancing flexibility differ so widely that definite correlations are difficult to determine. This is particularly true when there are no controls for heat treated files having the same design dimensions. D&S Dental, LLC provided identical files having different degrees of heat treatment for testing and determining correlations. One group of files had no heat treatment (Group A), one group had medium heat treatment (Group B) and one group had greatest heat treatment (Group C). Each group was tested for rotation until failure (suspended at 3mm from tip), peak torque at failure, and force required for 5mm deflection on a 60 degree inclined plane to measure tip flexibility. Group A, no treatment, values were used as base lines for comparisons.The results are as follows:
|Group B||Group C|
|Degrees Rotation to Failure||(+)61%||(+)33%|
|Peak Torque at Failure||(-)7.6%||(-)69%|
|Force on 60 Degree Incline||(-)12.5%||(-)26.6%|
Although there is an approximate direct correlation for peak torque at failure and force for 60 degree incline flexibility, the degree of rotation to failure appears to be an aberration of expectation. Within the scope of this limited research, we can conclude that heat treatment applied to enhance flexibility will accompany a decrease in resistance in torsional stress.