Negotiating around anatomic impediments: Tactile clues, bypass techniques, procedural flow

Without a clever technique for these cases, the right instruments, and an accurate mental image of the canal space you are in, you have virtually no chance of reaching the end of the root canal space, significantly increasing the chances of persistent apical infection. With the right stuff, managing these endodontic challenges can be a fascinating procedural experience requiring little extra time and delivering remarkably predictable outcomes.

 

Let’s begin with a look at the different types of impediments.

Anatomic impediments

• Apical irregularity at the terminus of a relatively straight canal
• Irregularity on the outside wall of a curved canal
• Abruptly curved canal

Iatrogenic impediments

• Apical blockage
• Apical ledging
• Remnant of instrument

How do you know you have met an impediment? That’s easy, by the tactile sensation felt as loose resistance to file advancement. Tight resistance to file advancement is the sensation felt when a file moving apically binds and then exhibits tug-back upon removal. Tight resistance means the file is binding on two opposite sides. Usually in this case, working the file (push-pull, balanced force, rotary, etc.) will allow it to progress apically.

Loose resistance to file advancement means that the file tip is caught either in some type of an irregularity (lateral canal, isthmus, fin), or the file tip is bumping into the outside wall of an acutely curved canal. All that remains in the diagnosis of apical impediment is to apply an apex locator (Fig.1) lead to the file and confirm a short reading (and obviously an apex locator is the best method of determining when you have actually reached the Holy Grail—length).

OK, so how do we deal with the aforementioned impedimento (Italian for impediment)?

First off, we do not ever attack or even firmly engage an impediment with the tip of any instrument. That’s how ledges happen, and a ledged canal is waaaay more difficult to manage successfully than just a severely curved canal. Aspire to the maxim, “If you can’t fix it, don’t fix it so nobody else can fix it.”

Managing impediments is all about file bending, mental visualization and patient, skilled technique. So let’s discuss file bending.

When and how to bend negotiating files

You might be surprised to read that I find it unnecessary to slightly curve all negotiating files before use — a method most of us were taught. Due to their exceptional flexibility, unbent K-file sizes smaller than #15 will easily traverse impediment-free canals with greater than 90-degree curvatures (Fig. 2).

Try using only straight negotiating files for a time — assuming you negotiate through a lubricant and start with an 08 K-file in small canals, You will be amazed at how often you get to length without bending them. At the end of the day, using cotton pliers with that ribbon-curling motion on your smallish files is a waste of time, so my advice is to stop yourself. You don’t have to do that anymore. Not doing that could save weeks of your life over a career.

Mental imaging

To understand this better try this thought experiment:

Be the file.

Imagine that you are the negotiating file moving into a canal. You have a subtle curve along your whole length, and because you are being used in a watch-winding motion your tip is waving back and forth “scouting” loosely through the canal — and, just as estimated length nears, “dink, dink” — loose resistance to apical advancement! Shoot! We pull back, re-approach and get the same result, regardless of how we manipulate the instrument (Figs. 3, 4).

To better understand why this has occurred, ribbon-curl a #10 K-file with cotton pliers along its full length and then clamp the file with a hemostat about 4 mm back from the tip. Look at the tip portion with magnification and you will see an essentially straight instrument tip. And this is the part of the file that is supposed to make its way around a canal path that is radically more bent.

Another way to say it is that the file tip was not bent acutely enough to keep the file tip centered as it moved into the tightly breaking canal curvature. When a file is curved 25 degrees along its whole length, it will never make it around a canal curvature that is 90 degrees along its last 1-2 mm.

Clever technique

Mentally imaging the canals you are treating, coupled with the use of appropriately curved files just needs a bit of clever technique to conquer the apical impediment. The first clever technique trick is to pre-bend the last 1-2 mm of the file with an EndoBender (SybronEndo) (Fig. 5), look down the length of the file and carefully adjust the indicator on the stop (notch, line or point) to be in line with the bend of the file.

Now, as you scritch-scratch into the canal, hunting for the path of least resistance, you feel and see the file passively drop deeper into the canal as you advanced in a new direction. Now, after you have successfully snaked the file around this one-of-a-kind, difficult anatomy, the next question is “How will I get back here with my next instrument?”

All you have to do is to look at the indicator on the stop, note the direction and after bending the next file and aligning the stop to the bend, you simply move the file to length with its bent tip pointing in the same direction as the previous file to length.

Final Advice

Remember that there is little forgiveness in a tightly curved canal, so for goodness sake, do anything to avoid blocking the end of the canal. Most often, compacted blockage at a canal curvature will never allow re-entry along the original canal path, so, despite a lot of effort spent attempting to regain patency, the most likely outcome will be apical perforation with these small instruments.

Use an apex locator, or you are working waaay too hard without a clue as to where you are. Is that acceptable to you when you could spend less time and definitively nail length with an apex locator (Fig. 6)?

Never initially thread the apical half of a small canal with larger than a #08 K-file. Never negotiate any canals without a lubricant in the access cavity.

Once you battle your way to length with that tiny first instrument, don’t just get patent a mm out the end of the canal—in this case I suggest you go 3-4 mm long and do 30-40 push-pull filing strokes to loosen the file and slightly enlarge the canal. This act will greatly improve your chances of avoiding blockage with the next largest file. There are few experiences more frustrating than to have cleverly and heroically battled your way to length through a hideously tortuous root canal, never to return again.

Distal canals of lower molars and DB canals in upper molars commonly have severely, abruptly curving canals enclosed inside remarkably straight external root structure. Look for loose resistance to apical advancement, when you feel it whip that instrument out, bend the very tip just short of 90 degrees, adjust the stop indicator, and go hunting!

Blocking, ledging or just never getting to the terminus because of a mishandled impediment is not the end of the world, but it’s not the end of the canal either.

Gone are those halcyon days when we could get away with telling curious patients that blocked canals were calcified apically. Never mind, apply these principles (Fig. 7) and I’ll see you at the apex!

Note: This article was published in Endo Tribune U.S. Edition, Vol. 7, No. 2, March 2012.