Managing Severe Canal Curvatures and Apical Impediments: An Endodontic Case Study

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Fear and anticipation. Those were the first 2 emotions I experienced when I looked at the preoperative radiograph my partner handed me.

"What do you think? Is it a case you'd like to take?" Jack asked me.

"Well," I said, "I guess I should be more careful of what I ask for, but yeah, it's definitely a lecture case if I can pull it off. Let's put him into my schedule. Thanks...I think."

I had been lecturing so much that I was only able to practice 1 or 2 days a week, and at that rate I didn't see enough patients to get the number of dramatic cases I needed to update my "Art of Endodontics" presentation. The last thing I wanted was for any of my course attendees to get the impression that I didn't practice anymore. So I had asked Jack Sturm, my partner who does a strong 4 days a week at our office, if I could have any unusual cases that came through the practice.

READING THE RADIOGRAPH

 

 

Figure 1. Preoperative radiograph of mandibular first molar showing severe but smooth curvature of the mesial root and an abrupt kink in the distal root 3.5 mm from its apex. Note the lesion associated with that root encompassing the bent apical region with enlargement on its coronal aspect. The shape and location of this radiolucency is a harbinger of the canal anatomy contained in that root form.

The first thing that struck me as I examined the x-ray film was the gnarly kink in the distal root (Figure 1). It's pretty common for distal roots of mandibular molars to have distal curves or bends, but this one was unusual because it was bent at the junction of the middle and apical thirds of that root, nearly 3.5 mm from the apex, not at its tip as is usually the situation. It was also disquieting to see the canal decrease in size at the kink—an indication of branching.

Second, I noticed the sweeping, severe curvature of the mesial root structure. I saw 2 PDLs from the mesial osseous crest to the apical region, indicating a very broad root with possibly 2 separate root apices. The position of the apical lesion associated with that root indicated that it could contain canals with more than 90º of curvature.

It was the toughest procedural challenge I'd seen in a couple of years.

 

CONSULT

 

I did the consult, at which time I found that the periodontal and restorative situations were ideal. The tooth was asymptomatic and pulp-tested necrotic as expected. The pulp chamber was obscured by the full gold crown, but the canal diameters at the orifice level were a decent size, so I did not expect any serious access challenges. There were no medical contraindications to treatment, the patient was a nice guy who felt comfortable in the dental environment, and he quickly agreed to my recommended treatment. As a matter of course, I advised the patient of the challenges to success in his case and the possible need for a surgical retrograde filling of any canal regions I couldn't negotiate.

 

FIRST TREATMENT VISIT

 

On the next visit, the patient was anesthetized with 1.5 carpules of lidocaine with 1:100K epinephrine given as a Gow-Gates mandibular block, and one-half carpule of Septocaine (Septodont) given as a buccal infiltration. The high and wide placement of the Gow-Gates injection nearly always hits the spot, and Septocaine, with its exceptional ability to infiltrate through thick cortical bone, easily knocks out all of the accessory enervation entering the root ends of all mandibular molars. I don't ever use Septocaine for block anesthesia because of its likelihood of causing permanent paresthesia when placed next to nerve trunks.

 

 

 
Figure 2. LA Axxess diamond bur with its 0.2-mm diameter pilot tip and parabolic shape at the end of the cutting region of the instrument. The pilot tip acts like the ball-bearing guide on a router bit, and the rapid taper of the cutting portion creates a smooth funnel prep into canal orifices.

After placing a rubber dam, the access procedure was relatively uneventful, aided by the use of an LA Axxess diamond bur (SybronEndo). The extended pilot tip and the parabolic end-shape of this diamond bur (Figure 2) allow me, after initial entry with a No. 4 surgical length round carbide bur, to cut nearly 90% of the access cavity to ideal dimensions in about a minute without needing to look at more than the angle of the bur in the prep.

It's nice to have the water spray on for debridement and faster cutting without giving up any control, a situation made possible because the pilot tip acts like a router bit in its guided-travel around the perimeter of the pulp chamber. Because the pilot tip has a perfect radius and is only 0.2 mm in diameter, it is easily dropped into even small canal orifices to create a funnel shape that will guide everything into each canal. Angling the bur will often allow deeper penetration into canals, after which the bur is tipped up, gimbaling it on its pilot tip, to the ideal line-angle extension for the shaping procedures to follow.

Next I filled the access cavity with ProLube lubricant (DENTSPLY/Tulsa), which comes in a single-dose dispenser tube. Because this tooth was necrotic, there was less chance of blocking the canal with vital pulp tissue, but even cases that test nonvital and have apical lesions can have pulpal remnants near the terminus. Furthermore, with the outrageous curves in these roots, there would be no forgiveness of even a slight blockage event, so it made no sense to tempt fate by negotiating without a lubricant.

I am adamant about filling the pulp chamber with a lubricant before initial negotiation of any canal system. When undergraduate dental students are taught this technique, months go by in the clinic without a blocked case, and in my own hands it has been one of the simplest and most effective things I've added to my procedures. As an aside, coating negotiating files with lubricant placed on the tray paper is not nearly as effective as the pumping effect achieved when it fills the pulp chamber. The only reason I've seen my students refuse to fill the access cavity (eliminating the pedantic need for coating every negotiating file) is when their access preparation is poor, thus making it difficult for them to get files into canal orifices covered by lube.

 

Figure 3. Radiograph showing a No. 10 file in the distal root canal meeting an impediment. Figure 4. EndoBender pliers with ideally curved K-file. Note the smooth bend to the last flute, necessary when negotiating apical irregularities.

Out of curiosity, I first entered the distal canal with a No. 10 K-file, and I wasn't surprised to meet an impediment (Figure 3). I seldom take length determination films, since I trust my Root ZX apex locator (J. Morita) more than a radiograph for that function. However, I will always take a film during instrumentation if things get even the slightest bit weird. In this case, the instrument was headed nowhere near the apex or the coronal aspect of the dog-leg in the root, so I took it out, got a No. 08 K-file, put a bend at its tip (Figure 4) with an EndoBender plier (SybronEndo), turned the tear-drop stop to the direction of the bend, and headed back in.

 

 

Figure 5. Radiograph showing a No. 10 K-file in place around 160º of curvature in the distal canal. Note the centrality of this portal of exit relative to the lesion of endodontic origin.

Directing the file bend to the distal, I was able to move further into the canal than previously, so I touched the apex locator "y-stick" lead to the shank of the file and it read long—a surprise because I was not yet to my estimated length. I took another radiograph (Figure 5) and saw that the file curved about 160º and was headed directly into the coronal lesion! Interesting, but I still had not negotiated anywhere into the last 2.5 mm of the root, so I knew there was more to discover. After several attempts to sneak further apically, rebending the file each time and trying to jink beyond the first 2 canal paths, I became frustrated and decided to check out the mesial canals.

A new, unbent No. 08 K-file slid easily (lube still filling the access cavity) in the mesio-buccal canal to the length indicated by the apex locator, using a watch-winding motion with light apical pressure followed by several pull strokes to loosen the file when it tightened up. I adjusted the stop to the MB cusp tip, pulled the file out after taking it 1 mm long to establish patency, and headed back in with a No. 10 K-file. Same experience. When I attempted to work a No. 15 K-file to the same length, it was tougher sledding, and it resisted further advancement about 1.5 mm from length. Instead of beating on the No. 15 or working a No. 10 in 40 push-pull strokes, I did step-back enlargement.

 

 

Figure 6. Radiograph showing No. 15 K-files in the mesial canals at their terminal lengths. Note the rebend of the mesio-buccal canal and the 130º bend of the mesio-lingual canal. 

I used a No. 20 Ni-Ti K-file (Lexicon, DENTSPLY/Tulsa) in 2 Balanced Force cutting cycles and confirmed patency with a No. 10 K-file taken a millimeter long; the No. 15 was then easily worked to length. Negotiation of the mesio-lingual canal was virtually identical, and I took a radiograph with No. 15 files in each canal (Figure 6). The mesio-buccal canal had about a 45° curve in the distal direction in the coronal two thirds and a slight mesial rebend as it approached the terminus. The mesio-lingual canal appeared to have about 130º of curvature that became more severe as it approached its exit point.

I hosed out the ProLube with my air/water syringe so it wouldn't foam all over the dam when I used NaOCl. I irrigated all of the canals with full strength, fresh-scent Clorox (Clorox) and had my assistant measure a set of 20 Series GT Rotary Files (DENTSPLY/Tulsa) to the shortest of the mesial canal lengths.

As always, I started cutting initial shape in each canal with the 20-.10 GT File, using a light, steady apical pressure with 300 rpm and 275 Ncm of torque limit set on the control unit of my DTC Handpiece (Aseptico). Three cutting cycles were accomplished with this file in each canal, being careful to remove the file immediately after it stalled (spinning without moving further apically), cleaning it of the dentin debris packed into the flute spaces and then using it again. The 20-.10 cut about 4 mm into the MB canal before it stalled, on its third use, without being caked with debris—the indication that it is time to move down in taper size to the 20-.08 GT File. In the ML canal, the 3 cutting cycles advanced deeper, about 6 mm, due to that canal being straighter in its coronal two thirds.

The 20-.08 GT File, at the same rpm and torque limit, advanced twice before stalling in the MB canal, and it only cut significantly once in the ML canal due to the severe curvature it encountered there. The 20-.06 GT File (at 300 rpm and 175 Ncm of torque limit) cut twice in the MB canal and once in the ML canal before becoming ineffective, so I moved on to the 20-.04 GT File next.

The 20-.04 easily reached the terminus in the MB canal in 2 cuts, but it didn't want to cut to length in the ML after 3 attempts. So, I gave it up and went down to the next taper size—an .02—but it was a No. 20 Ni-Ti hand K-file used with 3 cycles of the Balanced Force technique and a light touch. Once the No. 20 K-file went to length, the 20-.04 Rotary GT File easily achieved length in the ML canal as well.

I irrigated with Smear Clear 17% Aqueous EDTA solution (SybronEndo) to remove the smear layer as I did apical gauging and finished both prep-arations. I cleared both apices with a No. 15 K-file, and my No. 20 NT K-file bound at length in both canals, with the No. 30 stopping 1.5 mm short due to the narrow initial shape. The terminal diameters of both canals appeared to be 0.2 mm, and considering the curvatures in these canals, I chose an .06 taper as my shaping objective in both.

The 20-.06 GT File cut effortlessly to length in the MB canal but balked in the ML, so I immediately removed it and pulled out a 20-.06 Hand GT File due to that canal's apically accelerating curvature. Using the Reversed Balanced Force technique (GT Hand Files have counterclockwise flutes), it easily cut to length in the ML canal in 2 cutting cycles.

With the EDTA still present, I confirmed apical continuity of taper in both canals after clearing with a No. 15 K-file. Sure enough, the No. 20 NT K-file still bound at length. The shapes were done in the mesial canals! I irrigated with NaOCl, dried all 3 canals with GT Paper Points, filled them with calcium hydroxide using a Temp-Canal syringe (Pulpdent), put cotton and Cavit (Premier) in the access cavities, and let out a sigh of relief. So far the case was still mine to lose.

The rubber dam was removed, the patient was given six 375-mg Naprosyn (generic) tablets, our usual postoperative instructions, and an appointment in 2 weeks for (hopefully) the final visit.

 

SECOND VISIT

 

Anesthesia and rubber dam isolation were accomplished identically to the first appointment, after which the Cavit temporary filling was removed with a No. 6 round bur. NaOCl was used with a 30-gauge Maxiprobe needle (DENTSPLY/Tulsa) to irrigate the previously placed calcium hydroxide out of the 3 canals. This was followed by the use of a No. 10 K-file to establish patency in the mesial canals, by going to and through their apical termini and irrigating with NaOCl again. In the distal canal, a No. 08 K-file was bent and taken patent through the 160º curve that exited in the coronal direction, and irrigation was done again.

ProLube was used to fill the access cavity in preparation for the attempt to negotiate to the apical extent of the distal canal system. A No. 08 K-file was set at length for the coronally exiting accessory canal and was bent 90º in its last 2 mm. Turning the file to the distal direction, it was taken to length, was turned to the buccal, and carefully pulled back until a little bump was felt as the file tip clicked into the apical canal path upon its withdrawn departure from the accessory canal. The trick here was not to pull the file back far enough to engage the straighter, more coronal impediment.

Having an ambivalent feeling of caution and elation, I applied a light amount of pressure and watch-wound it back and forth 60º to 90º—it moved into the canal about a millimeter and stopped. After getting a precise finger rest, I carefully moved the file in and out about 10 times and attempted further apical advancement. Nothing happened, so I increased the apical pressure on the file as I watch-wound it with no effect. The file was withdrawn, rebent, and reintroduced in the same manner as before. Little apical progress was made, so the file was withdrawn.

 

 

Figure 7. Radiograph showing a No. 06 K-file, which was negotiated beyond the 2 more coronal impediments. Note the 2 directions of the canal curvature as it terminates apically.

My next move was to measure, bend, and place a No. 06 K-file to the point of contention, a strategy that worked as it advanced (with watch-winding) another 0.75 mm toward the apex of the root. When that file resisted further advancement, it was removed. The No. 08 and No. 10 K-files were worked to their binding points to create more room for the No. 06 file. The No. 06 K-file was rebent, replaced into the apical zone, and it advanced to length as indicated by the apex locator (Figure 7).

Several comments are ap-propriate here. First, negotiating files are never turned more than 90º in a clockwise direction—in these tortuous canal paths, they would instantly break. Watch-winding or careful counterclockwise rotation is safe and appropriate. Second, a moderate amount of apical pressure can be applied during watch-winding with file sizes below a No. 15, as these fragile instruments will usually buckle before they will ding or ledge a canal wall. When a file buckles, it usually exhibits resistance to withdrawal motion, so it is removed and a new file is bent and used. Finally, there is absolutely no chance of sneaking through these kinds of canal forms without a lubricant filling the access cavity so that it is constantly being worked into apical regions.

After setting the stop at the reference point, the No. 06 file was worked 2 mm beyond the terminus, and 20 or 30 short-amplitude push-pull stokes were used to loosen the file in the canal. The No. 08 file was worked to length fairly easily, as was the No. 10 file. However, it took a lot of step-back work with the No. 20 and No. 25 prebent stainless steel K-files, as well as an initial crown-down shape with a 20-0.10 GT Rotary File (short of the first impediment) to get the No. 15 to length. As always, I felt a great sense of relief when the No. 15 went to length, as 90% of the unknowns in the case had been resolved.

Serial step-back enlargement with prebent No. 20, No. 25, and No. 30 K-files was accomplished with 4 recapitulations. Each serial use of the 3 instruments was started with a No. 10 K-file being taken to and through the terminus to clear and ensure apical patency, followed by the No. 20 being watch-wound to its binding point, and then cutting dentin on the pull stroke. Typically, 3 of these watch-wind-pull cuts were made with each file before moving to the next larger file in the series. Again, after using the No. 25 and the No. 30, patency was confirmed with a No. 10, and serial step-back preparation started again with the No. 20. After each recapitulation of the series of instruments, each file fit closer to the terminus and its predecessor, ending with the No. 20 fitting to length, the No. 25 1 mm short, and the No. 30 2 mm from length.

At this point, there was tapered shape in the coronal two thirds of the distal canal and tapered shape in the apical 3 mm, but discontinuity of taper between those regions. To connect these 2 shapes, coronal and apical, I decided to use a Hand GT File, as a rotary file, with its shape memory, would never move past the first impediment.

 

 

Figure 8. Ni-Ti 20-.06 Hand GT File after radical bending to overcome its shape memory. This was necessary—with the teardrop stop turned to indicate the position of the file bend—to avoid the apical impediments and allow it to cut to the apical extent of the distal canal.

Using an EndoBender plier, I used a technique taught to me by Dr. David Rosenberg whereby the Ni-Ti Hand GT File was gripped by the plier's clamp jaw, was overbent to 180º, and was pulled firmly against the plier's bending fulcrum jaw. Dr. Rosenberg taught me that if I radically bend a Ni-Ti file, I can overcome its shape memory and impart a lesser residual bend of 35º to 60º, enough curvature to dance past a canal impediment (Figure 8).

After bending the GT File, the teardrop stop was directed to the position of the bend. The file was moved through the canal, first with the bend in the distal direction to avoid the first impediment, then to the buccal direction to avoid the second impediment. Immediately after bypassing the coronally curving accessory canal, the file tightened in the canal. At this point, the bend was irrelevant, so the file could be used in a rotational manner without consequence, specifically the Hand GT Re-versed Balanced Force Tech-nique.

The GT File was rotated counterclockwise (the direction of the flute twists) until it snugged tightly into the canal. Firm apical pressure was placed on the handle, and it was turned 360º in a clockwise direction. Initially, the file progressively tightened, and then at about 180º, it released and turned easily, having made the dentinal cut. The file was rotated further into the canal by again rotating it counterclockwise, and then it was reversed in a clockwise direction with apical pressure for the 360º cutting stroke. Three of these engaging and cutting cycles were accomplished before removing the file to clean it. It was rebent, negotiated past the impediments, and cut further into the canal. On the third set of cutting cycles, length was reached.

EDTA solution was used as an irrigant to remove the smear layer created by cutting dentin as the prebent No. 15 K-file was taken to and through the terminus, followed by the prebent No. 20 K-file, which bound at length, confirming apical continuity of taper. After using a No. 10 K-file to confirm apical and lateral patency and irrigating with NaOCl, the distal shape was done.

Conefitting in the mesial canals was easy despite the severe curvatures because there were no impediments. An .06 GT Gutta-Percha Cone was taken to its binding point in each canal, grasped by locking cotton pliers (at a right angle to the cones) lightly touching the appropriate reference point, and withdrawn. Each cone was measured and cut to a length 0.5 mm from the full length of its respective canal. Conefit in the mesial canals was complete.

Conefitting in the distal canal was a different story. The first cone I tried in the canal buckled at the first impediment, so I chilled a second cone in an alcohol gauze to stiffen it, bent it like a file, and made an attempt to bypass the irregularity. No luck. Then I had my assistant bring me a patient cup with ice water in it, chilled another cone, bent it, and tried again. No dice. After 7 or 8 tries, I decided that another strategy was in order.

While it is easy to fill laterally to the end of a fit cone, it is virtually impossible to fill beyond the apical extent of the conefit length in a well-shaped canal, so I thought of using a GT Obturator (DENTS-PLY/Tulsa). In the carrier technique I use with GT Obturators, a 1-mm gutta-percha and sealer front is usually ahead of the carrier when it reaches its final position 1 mm short of length. In this case, however, I had at least 6 mm of canal space beyond the first impediment. So, after irrigating with alcohol and drying the distal canal as best I could with GT Paper Points, I did the opposite of my usual technique.

 

Figure 9. Radiograph showing distal root canal system filled with a 20-.06 GT Obturator and GT Gutta Percha Points fit in the mesial canals. Note the fortunate apical accuracy of the fill at the terminal canal opening as well as filling of the other 2 portals of exit. The GT Obturator was pushed until it butted against the impediment.

I didn't strip off 1.5 mm of the gutta-percha from the carrier tip; I coated the canal liberally with Kerr Pulp Canal Sealer on a paper point. I didn't blot the surplus sealer with successive paper points and I didn't place the GT Obturator slowly over 6 to 7 seconds. I slammed it into the canal (after heating it) in 2 to 3 seconds—all of this with the intent to push more sealer and gutta-percha ahead of the carrier than usual. I placed the prefit cones in the mesial canals and took a radiograph (Figure 9). Wow! Three portals of exit were filled, and the apical terminus was filled to exact length—an amazing result considering the fact that the carrier stopped at the impediment 4 mm short of that point. The only disappointment was the lack of a sealer puff at the end of the most coronal lateral canal (the first impediment). This could mean that it was filled slightly short of its full length.

 

 

 

 

 

 

 

Figure 10. Elements obturation device with combined System B and Extruder (left and right respectively). Figure 11. Postoperative radiograph showing final fill of the root canal systems. Note the mid root and apical lateral canals in the mesio-buccal canal and the s-curve of the mesio-lingual canal.

The mesial canals were dried, and length was confirmed with GT Paper Points. Then the prefit cones were placed with sealer, the canals were downpacked with prefit System B electric heat pluggers, and then they were backfilled with the gutta-percha extruder from the System B/Elements obturation device (SybronEndo, Figure 10). The postoperative radiograph showed 2 lateral canals filled off the mesio-buccal primary canal (one mid root and the other apical), and the mesio-lingual canal exhibited a couple of accessory canals in the apical third (Figure 11).

 

 

Figure 12. Recall radiograph showing excellent healing at 6 months after treatment.

With great relief, I closed the access with cotton and Cavit, removed the rubber dam, and took final films. Six months later I saw the patient for a recall check, and healing was progressing nicely (Figure 12).

 

 

 

 

 

 

 

CONCLUSION

 

This case confirmed many things that I knew before I began it—namely, that bending files and using directional stops is the only way to negotiate challenging anatomy, that Hand GT Files are indispensable in shaping tortuous canals, and that luck is a part of most exceptional results. The new lessons this case taught me were how carrier-based obturation can be the most effective filling technique when dealing with impediment cases and how the variables involved in their use can be manipulated to lengthen or shorten the amounts of filling material that move ahead of a carrier.


Dr. Buchanan is a diplomate of the American Board of Endodontics and a fellow of the International College of Dentists and American College of Dentists. He is an assistant clinical professor of the graduate endodontic program at USC School of Dentistry in Los Angeles. Dentists interested in his videotape series, "The Art of Endodontics," and his intensive hands-on laboratory workshops in Santa Barbara, Calif, can call (805) 899-4529. For information related to this article, visit endobuchanan.com for GT updates and answers to frequently asked questions indexed by topic. Questions concerning challenging cases can be directed to (800) 528-1590.

Disclosure: Dr. Buchanan consults for and holds patents to the GT System of instruments manufactured and sold by Dentsply. He also holds patents for the System B Heat Source and is the inventor of the Continuous Wave of Condensation Technique as well as the LA Diamond Bur by SybronEndo.


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