Lump-Compression Probing

Revised May 12, 2005

A fact that you may not have considered since dental school is that the more recently laid down secondary dentin is softer than that that is older. That is, it is less mineralized and more organic than older dentin.

When odontoblasts lay down layer upon layer of secondary dentin they have to be alive to do that.

Now that may seem like an obvious point but it has some implications for getting through a tight canal.

As the canal closes itself off, it is usually the case that the last cells strangulate themselves and wither before laying down the last bit of secondary dentin in the exact center of a canal so what we have at that point is not mineralized secondary dentin but dried pulp tissue...more organic and softer than the layers further from the center.

As the pulp recedes from pulp chamber to pulp canal to apex laying down secondary dentin it alters the shape of the chamber and canal.

Usually the irritation is localized as in a carious lesion usually followed by a filling or a crown.

Which in turn causes irritation that causes more secondary dentin.

As the patient ages, wear, periodontal disease and other factors move the irritation further toward the apex and the entire pulp chamber gets filled with secondary dentin and the canals e.g. in a molar in effect become three or four separate root canal systems, isolated from one another.

It is these kind of teeth we are being called on to treat today.

Teeth where there very often is no longer an actual canal space except in the apical half of each canal the rest of it filled with dentin and/or pulp debris.

Each however has left a trail of softer dentin that leads directly to the center.

If we can use that as a guide we can often work our way through until the canal is actually big enough for our smallest instruments.

It is this concept that leads us to lump-compression probing.

In canals where there is no patent canal we can use a pointed instrument shaped much like a snow plough to force our way through the softer dentin and use the harder secondary denin as a guide to keep us centered.

To do this we need an instrument that has unique capabilities.

It must:

  1. be conical on the tip
  2. be able to withstand tremendous stress
  3. be able to get stuck and pulled back out without breakage and
  4. have a low helical angle so that it can be screwed in to make progress through somewhat solid dentin.

Fortunately, we have that instrument today, and if this sounds like a commercial for that product it is only because there is only one instrument that will do what I have just described.

That instrument is a Fine-Cut® Hand File made by Special Products, Inc. in Kissimmee, FL. And the inventor of that instrument is the author of this course and web page.

One of the unique features of this instrument which most would describe as a hedstrom (it's not) is that it can LITERALLY be pounded into a tooth with a hammer and pulled out with a pair of pliers and it will not break.

The reasons for this can be gleaned from the discussion later of instrument design factors and how they control what can be done with them.

The techniqe is as follows.

  • Insert the file until it wedges itself into the canal.
  • Pull it out.
  • Repeat.

Each time this is done, it will have moved further into the canal.

What has happened when you pulled it out is that whatever dentin was holding was chiseled away by the flutes and now the file can go further.

The limits on this procedure is how hard you can push, which is in turn determined by the size of the file and how much of it is in a portion of a canal that is large enough to allow the file to buckle.

Once buckled, all files are prone to breakage.

There are two ways around this.

You can:

  • Use a larger file, which is stronger and less likely to buckle or
  • Screw the file in instead of pushing it in.

Lets take the second one first.

Since a shaft of a file can take some amount of torque if you were to push on it and turn until you felt torsion, this would be an indication that the tip of the file is stuck in dentin, exactly what we did when we did push-pull-probing above.

Once the torsion is released then pulling the file out will again remove some dentin and allow the file to proceed further next time before binding.

Many times this can be used to break through the dentin that is closing the orifice of canals and once through, the canals are again large enough to do the normal push-pull-probing.

Remember the sequence for push-turn-pull-probing is:

  1. Push
  2. Turn until torsion is felt
  3. Release the torsion by letting go of the file
  4. Pull it free as in push-pull-probing

Here's a couple of hints that may help:

  • If there is no probe-able canal dig an explorer into the small brown spot on the floor of the pulp chamber that is the sign of non-mineralized secondary dentin using a good stiff endo explorer until there is a conical depression left.

    Then select a Fine-Cut® file that will 'bite' when you use push-turn-pull-probing.

    This may even require using something as large as a number, that's not a typo.

    Once you have made a small canal following the secondary dentin you can use the conical tip of that hole made by the larger files, as a starter hole for the next smaller etc.

    Ironically in many cases instead of going from small to large when probing, we go from large to small.

  • While probing, if several millimeters of file is in the canal, the file will get stuck really hard and pulling it out may in fact require a plier.

    Generally you can back up about 4mm and do a little circumferential filing with the hand file you are using to enlarge the canal just enough that the flutes do not engage except in the apical 4mm, but not large enough to allow the file to buckle within the canal.

  • In some cases, you may even use up several files in the process.

    If a file buckles, DO NOT ATTEMPT TO STRAIGHTEN IT. Throw it out!!

  • Straight push-pull-probing can be done holding a Fine-Cut instrument in a needle holder forceps.

    It is even possible to do a little push-turn-pull-probing this way.

  • When dressing an apex to size, clamp the file with a needle holder forceps at exactly the apical length and do push-pull-probing until the forceps hit the landmark.

    This will assure accurate measurement to the apex.

  • It is not usually necessary to precurve a Fine-Cut® file when probing. Very seldom is there a curve in a canal that the smaller files (15-25) cannot negotiate.
  • If you need to precurve a file, then only push-pull-filing is possible.