Pressure Filling

Most people do not distinguish between Pressure filling and passive filling much as non-football fans don't distinguish a line-man from a line-backer from a line-judge.

Pressure filling assumes one very important factor, namely that the needle is wedged in the canal. If the needle is wedged, there is only one place for the cement to go. In effect the canal beyond the needle is an extension of the lumen of the needle.

There are two critical factors in pressure filling.

First, you must have patency. That is, the air in the canal apical to the needle wedge point must exit before any cement can enter. If you do not have patency then you simply compress the air apical to the cement and as soon as you relieve the pressure, the air expands and pushes the cement back up the canal. By the way, this is also true of gutta percha techniques that fill from the crown down and do not provide a vent for the air.

Second, you must know how much cement to extrude. This has several implications.

If the pressure filling is a prelude to an apico, any extrusion can be removed during the surgery. In fact this was the first way injectable endo was done back in 1946.

Another way to control it is incremental filling. That is,

• add some cement,
• take an xray.
• Add some more forcing the cement apically.
• Repeat.

Until the cement is where you want it.

If you knew the volume of the canal beyond the wedge point you could then extude just the right amount.

This approach has two components, the calculation and the control of flow.

• Calculation is basically simple. A root canal is a truncated cone. That is a cone with the top lopped off. Since you know the minor diameter, i.e. the apical size. And you know the major diameter, i.e. the outside diameter of the needle you wedged. And you know the height of the cone, i.e. the distance to the apex. You can calculate the volume of this truncated cone.

• The other problem is purely technical. Do you have a syringe that is calibrated closely enough to deliver cement that accurately.

We have solved both problems...theoretically. The calculation is done by plugging numbers into a spread sheet to produce a table of all possible values for various needle sizes, apical sizes and canal lengths. The syringe is the new Cartridge Endo Syringe from Special Products(800)538-6835.

In fact the pressure filling part has been an important aspect of our passive filling concept for the last 40 years(Yep, I'm one of those old codgers that graduated in 1962). The needle is placed 1mm from the apex and a known, safe, amount of cement is injected usually about 1/16 to 1/8 turn, which moves the plunger 1/320 of an inch and extrudes about .007 cubic mm.

As the cement flows, the needle is withdrawn at a fixed rate to fill the apical 3mm. After that, the canal is large enough that even with zero tissue fluid pressure at the apex, the fluid friction of the cement apical to the needle tip, will prevent the cement from flowing apically. Once this point is reached the needle can be left in place while filling the portion of the canal coronal to the tip of the needle and the needle is withdrawn while backfilling.

This method is also a perfect adjunct to the use of an apical plug of gutta percha. After all even if you don't agree that you want to use cement in the apical portion of a canal, there is little reason not to use cement once the apex is closed. (See Journal of Endodontics April 2005) This concept enables one to use circumferential filing in the coronal aspect and rotary NiTi filing for only the apical 3-5mm...but that is an entirely different issue.

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