Beginner’s guide to Apical Gauging

Most Dentists don’t know about this technique! Do you?

 Do you do apical gauging for every endodontic case?

Why is it that sometimes GP extrudes beyond the apex of a tooth during obturation?

Why is it that after using the warm vertical condensation obturation technique, GP is forced through the apical foramen?

How do you avoid cases like this?

over-fill extrusion of GP
Extrusion of filling material into periapical tissues, in this case – the mental nerve bundle

The simple answer? Apical gauging has not been done!

Apical gauging is a technique to best determine the size of the apical constriction and the taper of the apical portion closest to the foramen.

Apical gauging helps with:

  1.  Choosing the best master cone that closely matches canal length and taper
  2. Achieving true tug back – as opposed to false tug back!
  3. Minimising GP extrusions during obturation, especially with warm vertical compaction/condensation.

How do you do apical gauging?


  1. Establish the depth of apical constriction – this is the zero reading on your apex locator. Remember your working length will be 0.5mm – 1mm short of this.
  2. After cleaning and preparing the canal system to your working length, passively insert 02 taper hand files, starting from #15. If the file goes past the apical constriction (your working length + 0.5-1mm), then choose the next largest file and repeat.
  3. When a file passively binds short of the apical constriction, that will be the upper limit of the apical constriction diameter. The smaller file before that would be the lower limit. See the example below.

Apical Gauging example

In this example, ISO 20 passively goes beyond the constriction, whilst ISO 25 binds short of the constriction.

This tells us that the apical constriction has a diameter of >20 but <25. (i.e. > 0.2mm but < 0.25mm).

You can estimate the taper of your apical preparation in many ways including:

  1. Trying different tapered GP cones to see which binds to length
  2. Trying different tapered files to establish which bind to length e.g GT hand files

See the discussion on understanding file tapers.

For each endodontic case, prior to obturation, apical gauging should be done! For cases with larger/more open apical constrictions, this technique becomes even more vital to reliably and safely obturate a canal system.

Images adapted from and dental protection


  1. Abir

    I would like to be part of your nice group.

    1. irfanjiwa

      Sure, you can get involved in our Facebook page

  2. Dr aditya

    Would like to learn more

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