How to select a device and become comfortable using the latest
generation of foramen-locating devices.

by Martin B. Goldstein, DMD, Wollcott, CT

If you regularly perform endodontics and have yet to incorporate a quality electronic apical foramen locating device (ALD) into your routine, you are passing up a genuine opportunity to increase the accuracy and consistency of your fills and save precious time.

The time spent taking working length and multiple check films along with development times can add as much as fifteen minutes to any endodontic visit. This is often enough to prevent a single visit completion. Dividing an endodontic fee over two visits, when the second visit involves nothing more than gaining access, irrigating and obturating, may negate the profitability associated with endodontic treatment.

And there are other benefits to electronic apex location ...

Nothing is so comforting during a procedure as to have a confirmation of your instrumentation efforts just moments away. With the ALD probe resting comfortably near your rubber dam (perhaps perched on your patient’s bib), you need only pick it up, touch your seated file, wait for a quick reading and think “Ahhhh, I’m still there; just where I want to be!” And it didn’t take you five minutes to find out. This rapid reassurance and peace of mind are a great psychological boon. Even in a weepy canal, you know you’re not over-instrumenting the apex.

By the same token, when straightening a very curved canal, you’re alerted if you alter the working length.

If suddenly your readings become unstable, you may suspect that you’ve packed some sludge apically and are in danger of losing canal patency. Time to stop, irrigate and recapitulate.

And all this information was available without anyone de-gloving or having to get up from their chairs. Talk about saving time (and gloves!!!)

Your patients will be exposed to far fewer RAD’s and will spend less time in your chair. A study a few years ago at the University of Tennessee concluded that routine use of an apex locator can reduce X-ray exposure by up to 66%, even when it is used very conservatively. They used it only to position the file before taking an initial radiograph.¹

Once you’ve learned to speak its language, the ALD provides a constant monitor of your canal-shaping progress. “ALD Speak” varies from unit to unit, but once you’ve learned to trust and understand its readings, your results will reach a level of consistency that you never thought possible.

The competency of today’s devices far surpasses what was possible only a few years ago. You can now locate an apex in any fluid you’re likely to encounter with incredible accuracy. Be advised, however, there still are devices available that haven’t embraced the newer concepts I’ll discuss below. When trying a device, check with the manufacturer to see if their electronics work in all fluids, and make sure that the device is returnable if you are dissatisfied.

How electronic foramen locators work

The purpose of this article is not to make you an expert on the scientific principles of an ALD. In the event a patient asks you how they work, however, (Hey, you never know) here are a few tidbits that will most likely satisfy their curiosity and hopefully yours as well.

Dentin, enamel and cementum are electrical insulators. Soft tissue (including the periodontal membrane) is a conductor. All ALD’s establish a circuit in the mouth that originates in the device, runs through your file via its attached probe, extends down the canal, out the apex and into the periodontal membrane. The circuit continues through your patient’s mucosa and eventually completes the loop by hopping onto the supplied lip clip that is connected to the ALD through a return wire.

As your instrument descends the canal and approaches the soft tissue at the apex, the strength of the signal arriving back at the instrument gets stronger and stronger. When the file reaches the highly conductive periodontal membrane at the apex, there is a huge jump in the strength of the signal.

Early electronic apex locators monitored either the resistance or impedance of a single frequency. Some required calibration while others didn’t. Such ALDs were easily confused by conductive fluids such as sodium hypochlorite or local anesthetic. If your technique involved either of these, you had to flush them out thoroughly using water and paper points before you could take a reading. In many instances, preparing the canal to allow an accurate reading became a science unto itself and totally eliminated the “convenience factor.” When gizmos are inconvenient, we’re apt to leave them sitting on the shelf.

Japanese dental researchers discovered that when two different frequencies were sent down a canal contaminated with conductive fluid, each signal would be distorted to a different degree, but the amount of distortion was proportional. This allowed them to develope an algorithm that used the relative strengths at these frequencies to compensate for the distortion. For the first time, it was possible to electronically locate the apex when the canal contained conductive fluid.

Though the mechanism of operation varies somewhat from instrument to instrument, the new “All-fluid” devices use signals consisting of two or more frequencies. They compensate for any shift of the test signal caused by conductive fluid using the other signal as a reference. The bottom line is that the latest generation of ALD’s work very well, and if you do endodontics, you shouldn’t be without one.

The Analytic All Fluid® (now owned by Kerr; street price approximates $1000)

My second love affair began shortly after taking a Steve Buchanan course. At this time he professed to use the Analytic device, and wanting very much to emulate the master, I purchased one.

The AF is boxy, also short in stature like the ZX and is characterized by a dual LCD display that is at times difficult to read if the unit is not angled properly towards you. It tends to reflect overhead lighting.

It sports a monochrome display, has a staid, professional look to it and could be described as the least-sexy-looking of the units discussed. It’s control panel is of the touch pad variety which allow for the AF to be tweaked to your personal preferences. That is, one can alter the readout to correspond with where you typically like to work your canal lengths, in essence creating your own apical landmark. It’s not a bad feature to have, but I never found the need to use it. The factory settings were just fine.

The AF visually tracks canal length by a broad LCD bar that extends to the right as you progress down the canal. This display is accompanied by markings in half-mm increments. When you penetrate the forbidden zone, the bar begins blinking on and off.

An additional but narrower bar is found atop the “canal read-out” and is intended to inform the user of the relative “wetness” of the canal. The AF wants that bar to rest in the center of the display, which indicates a moist, but not flooded canal. It is said to have greater accuracy when this is the case, a claim with which I concur (figure 8)

The Analytic AF, when ordered can come with a spring-loaded clip or a forked probe that requires only that you touch the file with the notched part of the fork. I much prefer this method of probing, as it allows more freedom of file placement. The user becomes less apt to dislodge the file by merely touching it as opposed to grabbing onto it with a spring-loaded clip (figures 4-6.)

Its lip clip is a broad, flat affair that’s effective at staying in place, but is difficult to clean owing to a narrow curvature where the lip is engaged.

The AF turns on automatically when a circuit is completed which is a nice convenience. One needn’t remember to turn it on, it does it all by itself and will turn off independently when you haven’t used it for several minutes. I’ve found the ALL FLUID to be very accurate and obtain my best obturation results when I settle upon a working length that finds the LCD bar .5 mm short of the indicated apex.

Summary: Like the RZX, the AT is a worthy piece of equipment that accomplishes what it sets out to do. It also can be purchased as a combination unit that incorporates an electronic pulp tester as well. The Analytic All Fluid is currently marketed by the Kerr Corporation.

The Parkell Formamatron® D-10. ($495)

Parkell has been offering an ALD for years, but prior to its new D-10, it had fallen to a lower rung on the ladder, because their older model (the Foramatron 4) was a single frequency device that was confused by conductive fluids. It worked. It just was less convenient to use and had more rules and regulations to follow.

Parkell has enjoyed a reputation for marketing electronic dental devices that though they sometimes possess fewer do-dads, perform well at a very attractive price. Witness their wildly successful ultrasonic scaler and their very competent electrosurge unit. I have owned and operated both for many years and have never been disappointed.

Enter the D-10. Finding it difficult to resist a new ALD (and actually needing a third one in our group practice) I chose to see if Parkell had turned the corner with this newcomer. I knew full well that they would take it back if I found it unable to “measure up” to the establishment. (I could’t resist the pun. Sorry.)

The D-10 has a funky look to it, but the innards are all business. While I encountered some slight inconveniences in its design, I found it to be a very competent device and was fascinated by the fact that such accuracy could be had for half of the cost of its competitors.

The D-10 does not feature an LCD read-out (cost-containment factor) but is instead adorned by a string of colored lights that descend on the schematic of a stylized root. When you are far short of the foramen, the tracking lights are green. They switch to a cautionary yellow when the file tip approaches close to the foramen. A large red light identifies the apical foramen. As your file descends, the lights turn on and the device beeps at you. As with the ZX, apical perforation is signaled by an alarm, as well as an illumination of lights that indicate you’re out of the root. These lights are orange.

The display is more dramatic than the ZX or AF, and is effective at cuing the operator when he’s hit pay dirt. Working length can also be monitored by sound only. That is, you needn’t look at the display once you’ve learned what the indicator beeps mean.

The D-10 comes with both a clip probe and a forked touch probe as well as a slightly cumbersome lip clip. The cabling is light weight, at first appearing fragile. This first impression turns out to be false as the cables can endure considerable handling and stretching while remaining intact. The lip clip works but is not as stable as those with the other units described. I found myself holding it steady with a free digit on several occasions.

The D-10 also has a dial on-off-volume wheel, much like a transistor radio that allows the user to reduce the tonal volume. When the unit self-turns off after 20 minutes of inactivity, the operator must turn the dial to the “off” position and then back to the on position to re-enable it. This is a minor inconvenience, but sometimes awkward for the gloved hand.

The forked probe is useful but will probably be thinned in a future design that will enable easier file engagement in canals that are nearly as long as the files used to measure them (figure 6).

The D-10 is light in weight, something my assistant loves. It features a rear bracket upon which the unit’s cabling can be wrapped when the unit is put away (another feature appreciated by my assistant.) Beware, however: the lightness of the unit and its angled stance makes it somewhat less resistant to being accidentally knocked over.

On the other hand, the snack-pack, cereal-box sized case allows easy storage.

I found greatest success when I determined my working length using the yellow light that precedes the large red APEX light. In fact, I had the impression that when the red light was steadily lit, my instruments appeared on the confirmation film to be just out of the canal.

This is where “ALD-speak” comes in. Each one of the units has certain performance quirks that become apparent with repeated use. In time the user begins to know what they mean and can discern the difference between a stable, accurate reading that can be trusted, and one that may require film verification or further canal shaping before the reading becomes rock solid. Once the user is comfortable with a device, there’s no mistaking the look of reliable readout indicating that the file terminates just short of the apex.

Without hesitation, I trust all three of these apex locators for final fills, sans film. This trust develops over time, but once established, it renders the ALD a tremendous time saver.

Summary: The Parkell Foramatron D-10 represents a trust-worthy, reasonably well designed ALD that has broken a price barrier for instruments that feature such versatility and accuracy. I have no trouble using it interchangeably with the other two instruments described.