Greeley, CO...June 17, 1994
What do a flagpoles, a fishing rods and an endodontic files have in common?
They all are applications of the notched beam concept.
There is a principle in engineering called the notched beam concept. That isthat if you bend a beam the metal gets compressed on the inside of the curveand stretched on the outside of the curve. This applies to all kinds of metalbeams small and large. You may have noticed that flag poles, light poles,buildings and fishing poles are tapered. This is done to distribute thestresses throughout the entire length of the beam.
If you permanently bend a beam at any point or if you cut a notch in the beam,all the stress and distortion of bending is concentrated at that point. Thisis why you must discard any file that has a permanent distortion in it.
If you attempt to pre-curve a file by using a hemostat or a pair of pliers,you only succeed in putting a multiplicity of small permanent bends in thefile, any one of which can receive all the stress and can break.
If those small bends are continuous then each takes its share of the stress and the file can bend without breaking.
The method we use is to hold the file flexed against a piece of 1/16th inch silicone rubber. ( Like the one you got in your tool-kit at the course ). Place the round tip of a closed hemostat against the file at right angles to the file near the tip of the file, press down until you depress the file into the rubber and then slide the hemostat toward the handle of the file.
Note March 1, 2003....There is now an excellant tool specific for this purpose. It looks like a miniature lawn roller from which derives the name, "MLR File Curver". The file is simply flexed against a sheet of rubber and the roller is rolled over it, in either direction until the file has the desired curvature. Price is $39 at the Special Products On Line Store.
The result is a curved file with no sharp bends. And it is easy to do.
P.S. It works even better on needles.
Here's how easy it is.