It was replaced by a far better device, the Fine-Cut Endodontic Handpiece in 1997.
The essence of circumferential filing is that a positive rake file, such as the Fine-Cut SPeed file is inserted into a canal, lateral pressure is applied and the file is moved in and out rapidly.
In order for any file to work each stroke must be long enough so that for each cycle, the file moves upward at least one interflute distance, that is so that the position occupied by one flute must now be occupied by the one below it.
This can be accomplished either by making the stroke longer or the interflute distance smaller.
Making the stroke longer means that if the tip of the file encounters an obstruction, pressure is put on the file to either poke into dentin causing a ledge or buckling the file causing breakage.
We have chosen to make the flutes smaller in order to keep the stroke shorter and avoid all these problems.
In addition, the file has to "float" in its holder. It cannot be held rigidly because if a curve in the canal is encountered, the file has to be able to accommodate and it must do it between two strokes. The Fine-Cut Floating Clutch first used back in 1983 for our Fine-Cut Sonic files and the Fine-Cut Sonic Adapters for sonic scalers still works and uses those same files.
How fast a file cuts is a function of:
Therefore the faster the file moves i.e. the number of strokes per unit of time, the faster it cuts, all other things being equal.
Driving the Fine-Cut Endo Handpiece with a faster motor cuts faster, smoother and with great efficiency. We favor the motor made by MTI, the Lynx Air Motor which has speeds up to 20,000 RPM which means that at full speed, the file is moving over 300 strokes per second.
In 1997 when this handpiece was introduced it was designed to be used with Doriot type connectors, the same type as on most prophy angles. It became apparent that the 0.092 inch diameter drive shaft collet on most dental air motors was not up to the task of driving a dental handpiece at the speeds needed for endodontic effectiveness.
In 2002 we decided to drop the Doriot connector and manufacture an E-type connector which eliminated the wear factor of the doriot connector.
Then early in 2003 a breakthrough in both technique and technology occurred.
The concept of differential force was introduced. That is the idea that to faithfully reproduce the circumferential filing motion done in the past by hand, that the amount of force of the "in" stroke had to be less then the force of the "out" stroke.
Instead of a cam driving what we call the 'rocker arm' of the handpiece, we use a cam to pull the file out, but a leaf spring to drive it in.
With the old design a file could get driven into a tight canal getting it stuck. The new design makes that an insignificant problem.
This also paved the way for expanding the usefullness of the handpiece to probing as well as circumferential filing and made possible wide ranging technique changes, in that most of the procedures done by hand could now be mechanized.
Probing is the simple act of driving a file tightly into a canal and then forcefully pulling it out, chiseling away what dentin was holding the file, simultaneously enlarging the canal, making it the shape of the file and proceding apically.
Working at 300 stokes per second, if the dentist feeds the file into a canal for instance one millimeter per second, the file actually engages, chisels and disengages every 300th of a millimeter to the point where the dentist hardly notices the action.
If the dentist feeds it faster than the handpiece can cut, the pressure upward on the file simply pushes against the spring and disengages the cam and the cutting action stops creating an audible cue to the dentist.
As we have often said, with circumferential filing, you can open a canal to any size with any file that will initially fit into a canal. Now the canal can be opened as well.
This opens up great technique possibilities.
Now to the third of those items.
For the most part, the coronal two-thirds of the canal prep has simple requirments. It has to be big enough to get your sealing instruments in and it must be clean. Even with gutta percha techniques, it doesn't have to be round. The shape can be dictated by the anatomy of the tooth.
Circumferential filing serves us well for this part.
Where the requirements get tighter is in the apical one-third, the "Apical Zone" in our parlance.
For syringe filling, the canal must be large enough to accept the size needle we choose for our syringe. In the case of our cement filling method, a 30 gauge needle is the standard which requires that the canal be larger than 0.30mm within one millimeter of the apex.
With injectable molten gutta percha, the canal has to large enough to accept a 25 gauge needle which is 0.49mm.
Most warm gutta percha and the newer fiber fill methods have additional requirements, namely that the canal be large enough for the condensing instruments, be round in cross section and that they have a specific taper.
This can be accomplished in two ways. Either by rotational reaming or push-pull probing as described above.
The taper is expressed as a ratio between the length of the canal and the increase in diameter. Thus an "02" taper gets 0.02mm larger for each millimeter of its length, an "04" by 0.04mm etc.
If a reamer is used, it must be that taper all the way to it's shank OR the canal must have greater taper above than below allowing larger instruments of lesser taper to approach the Apical Zone.
The problem with rotational reaming a canal is that if any of the instruments get stuck there is a likelihood they with twist off and thus many instruments of specific size and taper must be used in a specific sequence to minimize this risk.
Namely instruments designed not for rotation but for push-pull filing can be used if they are the right taper. This virtually eliminates the problem of breakage and actually eliminates the problem of breakage due to torsion inherent in rotation.
The Fine-Cut Endo System now has added 02, 04 and 06 tapers to its file sizes above size 30 and to make it possible to get around curves without precurving, they are made of Nickel Titanium.
You now have a system with no rotation and no possibility of torsional fracture that creates a prep that will be precisely shaped and sized for the gutta percha of your choice.
These and other items are available from the Special Products OnLine e-Store.
