Commack, Long Island, New York_October 10, 1994
Back in 1963, I did my first root canal with an endo syringe.
At that time there were no courses teaching the technique and I had to learn the hard way, by trial and error ... lots of errors.
The first endo syringe was the Pressure Filling Syringe from PCA.
It was basically a long threaded rod fitting into a long threaded tube. The needles available for it at that time were about 25 gauge which is the size of a number 50 file.
The recommended technique was called the Pressure Filling Technique and it didn't seem to work very well.
There were several reasons why.
First, the threaded rod in a threaded tube leaked.
There is no way to get a hermetic seal between male and female threads without them locking up.
Since the needle wedged several millimeters from the apex, there was a bolus of air trapped between the needle and the apex.
Before any cement would go to the apex, the bolus had to be blown out throught the apex.
And the leaky syringe varied as much as the back pressure at the apex.
Then in the eightys, along came the molten gutta percha syringes.
These had larger needles and thus wedged farther from the apex. Thus more air had to be blown out.
In the ninetys, we have finally reached the zenith.
Various gutta-percha-on-a-stick techniques are available and being heavily promoted. But there is a conceptual flaw in the method.
As soon as you put a drop of cement in the orifice and begin to insert the softened gutta percha, it traps a whole canal full of air in the canal and the only escape is via the apex ... fast, because the gutta percha is hardening all the while.
If the apex is non-vital, that is, if there is a granuloma, abscess, or fistula, the consequences are minimal.
You just blow bubbles which are gradually absorbed.
There is plenty of room for air.
But if the apex is vital, there is nowhere for the air to go.
It tears the periodontal ligament, causes bleeding and subsequent inflammation and pressure on an already injured periodontal ligament.
This explains the source of the pain that happens occasionally.
But this is not the real problem.
It's just a public relations problem between you and your patient.
It will eventually heal.
But suppose you are one of those dentists who has been trained that the apex is sacrosanct and should never be violated.
If you prepare a canal that does not have a patent apex, there is NO WHERE FOR THE AIR TO GO.
It just gets compressed.
Remember Boyle's Law from your high school physics classes.
It says that if you compress a gas to half its volume, the pressure doubles.
Compress it again and it doubles AGAIN.
Since a root canal is a cone, the diminution of the volume progresses geometrically as you push the gutta-percha-on-a-stick closer and closer to the apex.
You push down on the handle.
The air pushes up.
Since the stick cannot be pushed back, but the gutta percha and cement can, at the bottom of the prep you have the insertion tool and compressed air.
No gutta percha.
Gradually the air dissipates but by now the gutta percha is solid and the cement has set leaving a void at the apex of your prep.
If you use one of these methods, here is my recommendation.
First, seat the point as slowly as possible.
Second, make sure the apex is patent.
Third, if you don't have patency, use another method, which allows the air to escape coronally.
In fact if the gutta percha were to be shaped the same as a normal gutta percha point, it could be inserted by sliding it to place, allowing the air to escape until just before it seated (the Morse Taper Effect) and then pressure could still be applied to make it conform to the shape of the canal putting pressure on the cement to force it into lateral canals etc.