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:
|Degrees Rotation to Failure
|Peak Torque at Failure
|Force on 60 Degree Incline
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.
FILE NAME: One Endo
MANUFACTURER: D&S Dental
MADE IN: USA
FLUTES: 2 (S-shape, H-type)
SPIRALS PER 16MM: 3.5
HELIX ANGLE: 7.5º [fig. 2]
CUTTING ANGLE: (-) 40º [fig. 1]
DEBRIS REMOVING AREA: 38% [fig. 1]
ROTATION TO FAILURE: 510º
PEAK TORQUE AT FAILURE: 86.81 gf/cm
60 ̊ DEFLECTION: 3.56 g
PLASTIC DEFORMATION: 0º
FILE CORE AREA RELATIVE TO CIRCUMFERENCE AREA: 43%
FILE CORE AREA RELATIVE TO FILE X-SECTION AREA: 65%
- The degree rotation to failure is less than that for the Edge file or the ESX.
- The peak torque at failure is more than the Edge but less than the ESX.
- Interestingly, the One Endo was not superior in either the rotation to failure or deflection tests but was the only file that did not fail the Endo File Evaluator protocol. This is likely due to the One Endo’s blade that extends closer to its actual tip and the single blade opposed by a rounded surface and its reduced helix angle. These features facilitate greater efficiency in debris removal.
Fig. 1 : TIP X-SECTION
What differences do design differences make? We intend to find out. We are embarking on a very ambitious research program to test each part of every major file in production, from tip to handle. We have completely up-dated the computer controlled Endo File Evaluator to improve resolution of its sensors and motors and to expand its capability for performing new testing protocols. As such, we have created what I believe is not only the most objective means for evaluating endodontic files, but also the best method for testing file functions in a manner that is truly relevant within a clinical setting. We do this while letting the data determine the results for objective comparisons independent of operator skill or marketing bias.
What difference does this endeavor make? Our first objective is to finally determine how to minimize risk and maximize efficiency, how file designs relate to function, how function relates to canal anatomy, and how anatomy relates to technique. Our second objective is to present the Endo File Evaluator results using the numerous different parameters for testing, and to use high resolution images and SEMs in a manner that allows clinicians to save and apply the information to enhance their skill and treatment.
How will this process take place? About every ten days we will share test results and observations of only one segment of each file beginning with the file tips. Through this blog, we invite you to participate in discussions and critiques to create group research dynamics as this project progresses. Once all segments of the files have been covered, a composite of each whole file will be available as an endodontic reference along with any contributing assessments gathered from our readers. We will continue providing results as we find them through this comprehensive series of evaluations and add to them in the future as needed. We are excited to embark on this endeavor and hope you will follow along and contribute your own thoughts and impressions.