How To Get The Most From Your Apex Locator

I was reading a car journal recently, and came across a new vehicle that can actually parallel park itself. It made me think how helpful this innovation would have been 25 years ago when I was taking my driving test! Although not able to parallel park itself, an endodontic apex locator can guide you through the murkiest films ever to come out of a Peri-Pro.

Endodontic Apex Locators, when used correctly, save valuable time and increase efficiency. They can often help determine the location of the apex when the operator is unsure using radiographs alone, for example when superimposition of the sinus prevents an accurate length determination preoperatively.

Recently I have tried several new units; however I found their readings inconsistent and often times unreliable. Although the Root ZX is one of the more expensive units, I am certain it will be a valuable part of your armamentarium, instead of simply collecting dust on your shelf. This unit measures the length of the root by calculating the ratio of 2 different AC frequencies (400 Hz and 8 kHz), and is extremely reliable.

I believe the best manner to determine the location of the apex is by using a combination of more than one method. This would include pre-estimating the length of the tooth using an accurate pre-operative radiographic image. A size 10 or 15 file should be inserted into the canal at the predetermined length and confirmed with the apex locator. If the number differs by more than 2 mm I would suggest taking an initial working length film. Any adjustments should be made and the length recorded. A final way to confirm length of the canal after cleaning, shaping, and cone fit have been accomplished is to insert a paper point slightly beyond the apex. The wet end of the paper point will bend and the dry part of the paper point should be measured. This is the final confirmation of root length.

Four tips to increasing the accuracy of your apex locator:

1. Although most apex locators claim to work in moist environments, in reality they perform best when the pulp chamber is dry. There may also be occasions when the canals must be dry in order to get an accurate measurement.
2. The most accurate reading, regardless of what type of apex locator is used, is one in which there is a consistent reading on the apex locator as the file is advanced towards the apex. If the display on the apex locator is “jumpy”, (the machine fluctuates greatly when the file is advancing apically), try switching to the next larger size file. I find that simply switching from a size 10 file to a size 15 file will produce a more accurate reading.
3. When using an apex locator on a tooth having a metallic restoration (PFM, gold crown, or a large alloy), the apex locator will often give an inaccurate reading. An easy solution is to insulate the file from the metal filling or crown by placing a plastic bur sleeve just below the rubber stopper on the file. This is a great trick!
4. When treating an upper molar with roots in close proximity to the sinus the first reading is often the most accurate as the apex locator may erroneously read a file which is in the sinus.

Hopefully this article will allow you experience better results when using your apex locator.