Parabolic Funnel Prep Review

Minneapolis, Minnesota ... June 30, 1994
Latest Update Saturday, January 17, 1998

One of the most frequent requests that I get is for a quick review of the parabolic funnel prep.

The basic sequence of files depends on the individual case but there are a few principles you should keep in mind.

1. The only files used are Fine-Cut files...some hand files and some sonic.

2. Fine-Cut Files do not cause ledges.

3. Fine-Cut files can get stuck and be pulled forcefully out without causing them to break.

4. Washed field technique packs no debris.

Since we would not cause a ledge, no matter what the sequence of the files, the order of the files is simply the best and fastest way we have found to do the prep.

• Step I: Probe to the apex using a #15 Fine-Cut hand file.

  It is important to get a patent apex.

  Only in this way can you be sure that you have a good seal at the apex.

• Step II: Circumferentially file 3mm short of the apex using a sonic #20, 25, 30, 35 and then 40, or for the STS #20,25 and 30.

  None of these files should get stuck in the canal.

  If they do, there are several possible reasons.

  First, you might not have enlarged enough with the previous file.

  Second, the canal may be curved.

  Third, you are in another canal.

• Step III: Probe to the apex with a hemostat held #20.

  Note when holding a file in a hemostat or needle holder forcep, it doesn't matter whether that file is a sonic file or a hand file.

• Step IV: Probe to within one millimeter of the apex with a hemostat held #30.

  This is known as the McCombs modification or simply the McCombs prep.

  This allows the 30 gauge needle which is .29mm in diameter to get within 1mm of the apex.

  If you have difficulty getting a #30 to the 1mm point it may be necessary to go to the 1mm point first with a #25.

• Step V: Probe to within 3mm of the apex with a #50 Fine-Cut file hand held.

  This makes the parabola, which is a pressure relief area.

  The idea is to get this as close to the apex as possible without getting so close you endanger the apex.

  In some curved canals or in cases where you have done a step back preparation, it is not possible to get close to the apex and the parabola is not possible.

E-mail your comments to drjack@BetterEndo.com