Push-Quarter-Turn-Pull Filing

Push-Quarter-Turn-Pull filing is one of the oldest and least understood forms of enlarging a canal and merits some explanation is a course of this type.

First of all one should understand that it is not really filing. It is a combination of boring and reaming. Boring in the sense that it is usually done with an end cutting instrument. And reaming because the bulk of the dentin removal is done by the sides of the file.

It is done with an instrument that has a negative rake and thus requires a good deal of pressure to enable the blades to force their way into the dentin. This force is accomplished by the horizontal force vector created by downward force against a surface that has almost a ninety degree angle. Thus almost ALL of the downward force is translated into lateral pressure. Much the same way that a log-splitter wedge is used to create lateral pressure from downward force.

Since when downward pressure is applied the helical spiral blades will dig into the walls of dentin, if the file is rotated clockwise the tendency of the intstrument will be to pull itself into the canal and if rotated counter-clockwise it will tend to push itself away from the apex, this has lead to two different approaches to filing that are, from a cutting standpoint, identical.

When rotated counter-clockwise the technique is known as "balance forces' technique. What is meant by the term is that the upward force of the helical blades is 'balanced' by the operators apical pressure on the file thus keeping the flutes in contact with the dentin. From the standpoint of the negative rake angle of each blade, it matters little whether the blande moves one way or the other, i.e. clockwise or counter-clockwise.

But from a standpoint of fracture avoidance it makes a huge difference. If rotated clockwise the instrument tends to stick and when twisted, produce internal stresses. With counter-clockwise movement this cannot happen.

There are all sorts of mathematical analyses of this method but the above is essentially the gist of it.