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!
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.
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.
- 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.
Great article. I’m using mine incorrectly. I have to figure out my zero zero, don’t know if I do or not!! Thanks dr. Chopra.
Meena-I’ll show u the next time I come in for my cleaning 😂
Endo rct cases
Your tips are highly valuable but the very first tip was quite different from other experts who always advocate of using apex locater in wet canals.
Thank you! You can try both the dry and wet canals, and check them with radiographs to see which one works better for you.
Great article! Kudos on how thorough you have gone into detail on the subject!
Thank you Diwakar!
I read the morita apex locator and it warning against the use of rechargeable batteries, so is it ok to use rechargeable??
Hey Tania, thanks for your comment!! The batteries typically last a really long time in the J Morita unit, so you may be ok. I would go with the manufacturer’s recommendations. I don’t use that apex locator really, but I haven’t had any issues using rechargeable batteries on my other units.
Qif one of the walls of tooth is missing,does it affect the apexlocator reading?
Hi! Thank you for your post. No, missing walls should have no impact, unless it effects your isolation. But, you can always build up that wall or seal it off with something like Opaldam to keep any moisture out. Hope this helps.
Great article…when we get the zero zero on the apex locator is tht the true working length or we should be .5 mm short of it…
Hey there!! I use the 0.0 as my working length and what I instrument to. Once I started doing that, I have had less failures and people with persistent percussion pain after treatment.
Very informative tip’s …. Thank you so much..
Mam I put my working length 0.5mm short of the apex wt I think is that working length varies as we complete the bmp. If I put wl at zero zero then there might be chances of over instrumention. Give me ur advice tnxs.
Good apical control is important, but so is the proper working length. 0.0 is where I have started to clean to and I have seen a decrease in my own failures. Hope this helps.
Thank you for the tips. I have held all of your tips to strict adherence since using my apex locators back in the 90s. To be honest, when we bought our first one I thought it was a gimmick but after using mine ( updated since ) for basically 25 years , I wouldn’t do endo now without one. It’s as simple as that If things go smoothly I usually take a pre op and post op film for my cases unless I’m having an issue getting a reading then I go old school with file in place and radiograph or if I’m having hard times reading canals coming together or in case where a single canal splits into two then I may put the file in and snap a quick digital X-ray to help “read ” the anatomy. I’m a gp who enjoys endo so I do the cases I’m comfortable with otherwise I have no problem referring the case right from the beginning to the big boys or big girls that are my specialists. Last thing I want to do is open something up then find out “I’m in over my head” and then send it to you guys. I know it happens and is usually not intended by us GPs but it always amazes me to see you all do a case that I felt was really hard! A lot of respect for your advanced techniques and education but us GPs love knowing you are there for us. Happy new year and your articles are killer. Let’s all have a great 2021 and may those curves canals and the “thrill of the full” keep us all bonded in the brotherhood and sisterhood of the endo gods
Happy New Year and that you for being a part of my endo community! I love your mindset about endo, it is exactly the way it should be! Wishing you a very healthy and happy new year!
Maam I have just started my practice n I love doing endo n I find ur tips and blogs very useful .How much time does it take for access cavity n to explore canal coz I take 45 mins n I think it’s too much hectic for the patient. Please can u guide .
Accessing is very important, so take your time. It can take me long in some cases too. I promise that things will get better in time.
Mam as you recommended to use apex locators throughout the procedure of BMP, i had a query here,because once I get the working length i start using NaOCl so if I want to recheck my working length won’t my apex locator give a wrong reading or do I need to dry my canal every single time I’m checking my working length. Pls guide me on this. Thank you.
Sometimes my apex locator works when it is wet. These are just guidelines if your apex locator starts to act up on you. So, you will need to take the time to get to know your particular apex locator so you can know when to make adjustments when necessary. If it chirps, then dry it and try again. If it still chirps, turn it off and take a radiograph.
Root zx recommends use when canal is wet.
Definitely your advice can be tried.
Hope I can reduce errors.
Try both ways and see what happens!! Good luck!!
My question was when i switched on apex locator for first time on screen there was 0.3 should i change it to 0.0 my epex locator is e pex pro from eighteeth company
I have only used the apex locators that you see in the picture. I would suggest asking the representative that sold you the unit to get complete clarification. But, my assumption is that 0.0 is the where you need to go on all units. Good luck!!
Great advice!!! I always feel like I hate doing root canals. .. as you probably know from my referrals. I love reading your blog! Your blog always teaches me something new!
Thanks Rebekkah!! I am glad that you like what you are reading and it makes me so happy that they teach you something every week. We are always happy to take your referrals. See you soon.
Hey really liked ur post just the way u said someday I feel to throw away my apex locator😌just had some issues so I googled it got some awesome tips… Keep posting..
Thanks Dolly – I’ll keep posting if you keep reading! -Sonia
I’m so thrilled to have stumbled on this post – your explanations are very easy to understand. I am a dental student and in all honesty, endo is not my favourite subject nor my strong suit at present. However I am determined to overcome this and your blog will be an invaluable study resource for me going forward. Thank you for producing this content and making endo a less daunting subject!
Wow Sara – I’m so glad you found my blog. You are totally who I’m writing for!
Stay tuned for more-
Thank you so much!
Hello doctor , I love your work , thank you for inspiring . I have almost become a fan girl of yours 🙂 got a question ,is propex pixi apex locator by dentsply good ?
And thank you for reading! The 4 apex locators I’ve shown here are the ones that I love and I use them all equally, but I’m not exactly sure of the manufacturers. So I do recommend them!
how can we do when the length of the channel is greater than the length of the h files?
I have files that are 31mm, I haven’t had a canal longer than that!!
Sonia , if you feel confident about your 0/0 reading on your apex locator, do you still take a verification radiograph? Also, I agree that a loose fitting file can give u a false reading. I often time will use my SX1 file as the file and turn it clockwise until it goes to 0. If I need an X-ray the file will not move.
Hi Greg – I usually don’t take a working length radiograph. Instead I use my cone fit radiograph as my working length and to refine my lengths when necessary.
Good topic iItend to rely on paper point. Technique root XX can be a guessing game
Hi Todd – Glad my post was helpful.
I am using Densply apex locator. Sometimes after receiving signals for apex (some short of it) and further widening ,on sbsequent mesuring it does nor give sigal, or signals r idicative of short length for the same length. What could be the reason and how to tackle ir?
Hi Dinesh, you may need to calibrate the machine. In order to do this, I make sure my file goes out of the canal slightly, so that it touches the PDL. Then I pull it back to get a proper reading. Try that with a small file, such as a 10, and see if that works. Hope this helps!
Hello Dr. Chopra,
As everyone mentioned great post. I loved your SLOB rule explanation as well.
1. My question for Apex locator is that, if you have discrepancy between Working length of Apex locator and radiograph which WL would you consider?
2. Also, would you go par apex to confirm WL with apex locator?
Thanks in Advance.
Appreciate your time.
Sometimes my apex locator does not tell me the truth, so I have to trust my radiograph too. If it looks short, I extend, if it is long, I back it up. I always try to go out about 1mm with a small file to calibrate my apex locator and then I get my length. I hope this helps.
Hello. I have a question.Can use apex locator in open apex tooth? And in root resorption tooth
Yes and No. The apex locator will start to ring out once it hits the outside part of the tooth, so yes it still works, but it is hard to read the locator in those situations so you may still want to confirm with a radiograph.
Hi Dr. Chopra,
Thank you for your blog! It is very kind of you to share your knowledge. I love Endo when it works out! Sometimes the apex of the canal is shorter than the length of the root. How do you when that is the case?
Hi there! Since this is not something that you can see, I would trust what your apex locator is telling you. However, in the beginning I always recommend also taking a working length film to gauge your apex locator. Hope this helps.
So I encountered a case ( 36) where my file is inside the mesiobuccal canal (0.5mm short- confirmed on radiograph) but no reading is shown in my apex locator for this canal alone.
Remaining three canals show accurate reading on the apex locator.
How do I go about this?
That means that you are not at the apex most likely and you will need to advance your file.
Hi Doctor Chopra,
What apex locator would you recommend to purchase in 2022?
There are so many good ones. I think that the Promark is a good one or even the one by Kerr.