Passive filling makes an important assumption. That the needle is not wedged in the canal and that the path of least resistance is coronal rather than apical.

This requires a consideration of canal size at the extrusion point and a consideration of the tissue fluid pressure beyond the apex.

There is one simple fact that we have relied on for years.

  1. That is that if the apex is reasonably small, i.e. under size 30.
  2. And that the canal is a size 50 or greater at the extrusion point.
  3. And that the needle is a 30 gauge.
  4. And that the extrusion point is more that three millimeters from the apex.
  5. The path of least resistance is coronal.

As you can see this takes several techniques.

  1. First, the canal at the apex must be small.
  2. Second, you must use a sealer that will flow through a 30 gauge needle. This eliminates most sargenti sealers, molten gutta percha and most others. This leaves basically PCA root canal sealer, one of two that are ADA certified for both sealing and filling. PCA is specially ground and sifted to assure that all the particles in it will fit through the bore of a thirty gauge needle.
  3. Third, the needle must fit loosely, i.e. in a size 50 canal.
  4. Fourth that the dentist be well trained.

The Automated Endo Seminar has trained over 20000 dentists over the last 20 years and we continue to do so. Unfortunately, those of you who live in other parts of the world may find it difficult to attend. But now the course is available in hypertext on the internet, that problem may yet be solved. Additionally, if you are properly equipped, you can arrange a video conference seminar using iChat AV on the Macintosh. (There are other ways too but they are more expensive and cumbersome.)

This method has some technical drawbacks in that it is difficult to get a tooth opened to size 50 if the root tip is small or curved. Again, training helps.

There is another point that must be made. That is that if we keep the apex small and we only get pressure relief in a large canal, we must have another way to fill the apex. In fact we have been using a form of pressure filling of the apex for years.

We insert the needle to one millimeter from the apex and extrude a quantity of cement that, "we could live with if it went through the apex." And then, passive filling the rest of the canal.

Thousands of dentists have used this technique successfully on hundreds of thousands of teeth over the last twenty years.

The question is, why change now. The answer is, that we have now seen the way clear to taking the technique and personal skill that takes years of practice and reducing that to hours. With the new Cartridge Endo Obturating Syringe and the control it gives us, it is now possible to calculate the volume of a root canal and deliver that quantity consistantly and accurately. (If you are really a stickler for accuracy you can add the Micrometer Extrusion Control Device.)