Interflute Distance

Trigonometry and Engineering Principles Applied to Endo File Design and Why You Should Care

Most dentists I have asked have never looked at an endo file under magnification.
The main reason seems to be that even if they did, they would not know what they were looking for.
That is, they would not be able to relate what they are seeing to what effect it has on the use and usefullness of the file.
It's sort of like looking for a tool to cut a tree branch and picking up a hammer. Sure it would work, but a saw would be better.
There are differences between one file and another as profound as the difference between a saw and a hammer.
I will attempt to explain them here. And to do that I have to 'dissect' and endodontic file for you.
Take it apart so to speak and look at the individual parts.

The interflute distance is the distance measured from one flute to the next.
Simple enough? Not so.
The assumption here is that there is only one set of flutes on a file.
Some files have one, two or even three sets of flutes intertwined, sort of a double or triple helix, to coin a phrase.
This is very obvious on a file where the intertwined flutes are of different design as in the K-Flex file on the left in the photo.
The importance of double or triple flutes comes in when using the interflute distance to calculate helical angle.
The helical angle is in effect the angle of a right triangle whose height is the interflute distance and whose base is the circumference of a cylinder around which it is wrapped.
Thus by...

...measuring the interflute distance and the diameter and
...deriving the circumference by multiplying by pi,
...dividing one by the other, and
...looking up the ration on a table of tangents
...we can determine to a high degree of accuracy, the helical angle of a file by simply looking at it's picture.
A problem enters when there is a multiple helix.
In these cases it is necessary to skip every other flute when measuring the height of the triangle.
The implication of a double helical design should now be apparent.
That is all other things being equal, if there are two helixes then the helical angle must be greater, as compared to a file with a single helix.
If you have an interflute distance of one unit.

And then compare to what you would have it you were to attempt to put one flute of double the interflute distance in the same area

and then to put two of double the interflute distance overlapping so that the flute frequency is the same as if the interflute distance was smaller

you can see that in order to have the same flute frequency with a double flute you would have to increase the helical angle.
The point is that it can be confusing to determine the actual interflute distance when there is a double or even triple helix design.
If a file is going to be used for circumferential filing, it is desirable to have the lowest helical angle as possible.
If it going to be used for probing is is essential.
The only way this can be accomplished is to have a single fluted design.
The implications of the helical angle affect how you may use a file and whether it breaks under a particular kind of use.
If a file is rotated and the helical angle is steep, it probably will not dig in and thus probably not break.
If a file has a low helical angle and it is rotated it will dig in very quickly, i.e. with not much of a rotation and will twist itself off very quickly.