Some days I adore my apex locator, and some days I want to throw it right out the window. Because root canals are no easy task… even when you have all the right tools. Take for example that handy apex locator—some days I’m pretty sure it lies to me. Anyone else trapped in a love-hate relationship with this thing? Apex locator accuracy is a super-common complaint I hear all the time!

At first, I thought, OK, give the thing some credit. I thought, maybe it’s just not the best apex locator on the market. So what did I do? Well, I eventually ended up buying every single model available in search of the best endodontic apex locator. 

No, I’m not making this up! I’ve got ‘em all. I have the traditional Root ZX, the Root ZX2, the PAL by Brasseler, and the Promark by Dentsply. You name it, I bought it!

And I’ve tested them all, so you don’t have to!

7 Tips for Troubleshooting Your Apex Locator 1

The winner is…

JK. After buying every endo apex locator, now I can confidently say that they all have identical drawbacks. 

The main problem when it comes to apex locator accuracy? I’m going to be honest here, it’s user error. Yikes. 

That’s why I want to share some tips on how to use these things so you feel like a boss with your apex locator.

Tip #1 for apex locator accuracy: prep appropriately .

Start here: Make sure your canals are dry! 

A dry canal will give you a more accurate reading, plus your machine won’t be chirping at you the whole time. Take some paper points and make sure to dry it thoroughly. Ensure your canal is free of sodium hypochlorite, EDTA (this is the biggest offender), or even pus, and then get in there and make another attempt to obtain your working length.

Tip #2: Make sure you are using the largest endodontic file possible.

I usually use my 10 file to get my initial working length, but if the canal is too big, this file will give me an inaccurate reading. The readings on my machine will bounce all over the place, but if I increase my file size to a 15 or even a 20, I will get a steady reading that gives me the accurate measurement—which is what I’m after! On the flip side, if you are short of your working length, then decrease your file size.

Tip #3: Pull your file away from metal fillings or crowns before taking your reading.

When your apex locator is in use, make sure your file is away from the sides of the tooth, as well as any metal fillings or crowns. If your apex locator is chirping at you, something’s up! And the problem just might be that your file is in contact with metal while you are using it.

Tip #4: Just take a radiograph!

Sometimes, I just turn the damn thing off and go old school. I place my file and take a working length film. The radiograph will tell you about the tooth anatomy.

If you’re a dentist who is just starting to dive into doing your own root canals, I suggest using both the apex locator and taking a radiograph, anyway! Taking a working length radiograph with a file in each canal is really helpful in understanding your anatomy. You will know when your canals join and when they are separate. I’m a big fan of knowing what to prepare for before I go into a tooth. 

Why is this so important? Well, you don’t want to instrument with your rotary file past the point of juncture on your joining canal. That’s a very common area for a file to separate. So play it safe and take smart measurements. One canal should be instrumented all the way to working length, and the other joining canal should be instrumented to the level where the two canals join.

Tip #5: Charge it up!

Make sure your apex locator has a decent charge or it may not be accurate. I have to swap out the batteries in mine from time to time, so I invested in some rechargeable ones and always have some charging just in case my batteries die spontaneously!

Tip #6: Use your apex locator throughout your procedure.

Interferences could affect your working length. I’ve experienced length shrinking up a bit as I work, and sometimes I lose patency because debris has blocked me out. Yikes. To troubleshoot, I like to use my apex locator throughout my procedure to make sure things haven’t changed as I go.

Tip #7: Go to “Zero Zero!”

These are the wise words of a teacher of mine. He would prance around our clinic and say, “You gotta get to zero zero. That’s it! It’s that simple!” There was no question about it. Well, what does that mean? It took me so long in my residency to figure it out, but now I know how right he was. These are words I live by now in my career.

Every apex locator has a different way of notifying you of when you hit this sweet spot. This should always be your end goal. If you don’t nail it, the chances of your root canal failing and your patient having issues later on goes way, way up!

In the endo world, a millimeter is a mile, so don’t dare cut any corners. Understand what your apex locator is saying to you, find that canal and get to the end of it. Every time. Zero-Zero (0.0) confirms that you are patent in your canal, that you have the true length of that canal, and now you can clean and shape properly.

Bonus Tip:

Here’s some extra credit when it comes to apex locator accuracy

Make sure that you are getting your initial reading by taking your file a little long to read the PDL, then back up your file short of working length, then re-advance it to your zero zero.  This will “calibrate” your apex locator and will give you a more accurate reading.

In short …

I am a firm believer in patency, and your apex locator is your tool to help you achieve that patency. An outcome study found that, in any tooth with apical periodontitis, if you are short by one millimeter, that this reduces your success rate by 14%. That is huge! So don’t be lazy, and get to 0.0 — and if it means that you need to bring the patient back because you ran out of time, or that you need to refer them to your specialist to finish it up, then so be it!

You will hear me say this over and over again: You always have to find all of the canals and get to the end of every canal. Start to pay attention to your working lengths. With enough practice you should be able to look at a radiograph and guess what the estimated working length should be for any particular tooth. (In fact, we like to have canine bets in my office to see who can guess how long the tooth is before we get our working length. I know, we are total nerds. Don’t judge!)

Want to geek out with me? Why not test your endo know-how with my quiz? I promise, I’ll fill you in on any blindspots so you can keep doing A+ endo. 


  1. Endodontic infection: some biologic and treatment factors associated with outcome: Chugal NM, Clive JM, Spångberg LSW. Oral Sug Oral Med Oral Pathol Oral Radiol Endod. 2003 Jul;96(1):81-90. PubMed PMID: 12847449.