Some days I adore my apex locator, and some days I want to throw it right out the window. I’m pretty sure it lies to me sometimes! I know I’m not alone. Who else has a love-hate relationship with their apex locator?
At first, I thought, Maybe it’s not the best apex locator on the market. I eventually ended up buying every single model available in search of the best endodontic apex locator. NO KIDDING. I have the traditional Root ZX, the Root ZX2, the PAL by Brasseler, and the Promark by Dentsply. You name it, I bought it!
After buying every endo apex locator, now I can say that they all have identical drawbacks. The problem was user error, so learn from my mistakes!
Apex Locator Tip #1: 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 dry it thoroughly. Make sure your canal is free of sodium hypochlorite, EDTA (this is the biggest offender), or even pus, 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. Again, 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 that I need. On the flip side, if you are short of your working length, then decrease your file size to get to the right length.
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, any metal fillings or crowns. Again, if your apex locator is chirping at you, something’s up! It could 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.
Why is this 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 batteries and always have some charging just in case my batteries die spontaneously.
Tip #6: Use your apex locator throughout your procedure.
As we instrument our canals, we remove interferences. This 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. 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 recognize how right he was. These are words I live by now.
Every apex locator has a different way of notifying you of when you hit this sweet spot. This should always be your end game. If you don’t nail it, the chances of your root canal failing and your patient having issues later on goes way up! Remember, 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. 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.
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.
Let’s sum it up!
I am a firm believer in patency, and your apex locator is your tool to help you achieve that patency. An outcome study1 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!)
So if your apex locator truly is on the fritz, you can figure out how to troubleshoot and what to do.
At the end of the day, understanding your 0.0 of your particular apex locator will have such an impact on the success of your cases… just wait and see.
- 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.