Written by L. Stephen Buchanan, DDS Wednesday, 31 December 2008 19:00
In his book Innovation and Entrepreneurship, business guru Peter Drucker stated that a new technology is not widely taken up by users unless it provides a 10X improvement over their current methods of work. This is certainly true in dentistry. Incorporating a new concept, technique, or instrument into a fully-scheduled day is a huge stressor. It also entails significant training costs for the dentist and staff as well as for the new inventory needed. Because of this, the most financially successful dentists watch carefully for the point in time where the benefits of the new technology outstrip the costs of taking it on. Only early adopters, who are driven by wanting to be on the cutting edge of technology, will jump in sooner.
When the 10X factor of improved results becomes a reality, clinicians who recognize these advantages can accomplish the treatment in less time, with fewer steps and greater confidence in the outcome. The new GTX Rotary File (DENTSPLY Tulsa Dental Specialties) with M-Wire metallurgy satisfies these requirements. As described in my article for Dentistry Today published in January of 2008 (see endobuchanan.com to download), this new file has the attributes of much greater resistance to cyclic fatigue failure—the major cause of instrument separation. In addition, fewer files and procedural steps are needed to create ideal shapes in root canals. As an improvement to the GT File line, the GTX Files have landed cutting blades for prevention of transportation, although the radial lands have been optimized. This has been accomplished by varying the land widths along the file’s length to increase their cutting efficiency without losing their resistance to straightening curved canal paths. Furthermore, the blade angles have been opened up (fewer twists) which also increases cutting speeds but also increases their flexibilities and the size of their chip spaces between the flutes.
All of these changes in efficiency were accomplished without forsaking one of the most unique features of the GT File line, the 1-mm maximum flute diameter (MFD) limitation which prevents over-enlargement of the coronal region of the root canal. This is a key factor in reducing the loss of structural integrity of the tooth after en-dodontic treatment. So, with the pre-existing safety features of landed cutting blades, limited MFDs, combined with the newly enhanced safety of R-Phase nickel titanium metallurgy, the only thing that could be better would be to reduce the number of files and procedural steps needed to accomplish shaping procedures in canals.
This article is intended to describe how these files are able to cut the shapes that are needed in most root canals, using one or 2 instruments with 4 to 5 procedural steps. I will detail the shaping procedures that were done by me and 2 of my esteemed endodontic colleagues in molars having moderate-to-severe canal curvatures.
CASE 1 MAXILLARY MOLAR TREATMENT
Figure 1. Maxillary molar with files in each root to lengths determined by Root ZX (J. Morita). Note the curvatures in the MB and DB canals, as well as the lengths in the palatal and DB canals that are short of the radiographic root apices but at the termini of those canals.
Figure 2. Postoperative radiograph showing conservative coronal shapes, apically accurate fills, and an ideally cut access cavity with the mesial and distal access walls parallel to the mesial surface of the tooth.
(This case was done as a live demonstration at the California Dental Association Meeting in Anaheim, California, on May 3, 2008.)
Figure 1 is a radiograph showing the final negotiating files in each canal. I would not call this a length-determination film because I do not use radiographs for that purpose since they are not as accurate as my J. Morita apex locator. This image was taken to demonstrate for my audience the curvatures of the different canals in this tooth. The MB and DB canals have obvious, significant curvatures. The palatal canal appears to be straight in this x-ray angle, but could be curved in the buccal or lingual planes, a possibility that will be discovered during the shaping of that canal. This image shows the negotiating prerequisite to shaping with GTX Files, a No. 15 K-file (or larger) to the terminus of all canals.
The shaping objective for GTX File use has been changed (streamlined) from that suggested for GT File shaping. Notably, the small canal shaping objective is now limited to a .06 shape and the shaping objective for medium-large canals is typically limited to a .08 shape. This is with the understanding that some medium and large canals may occasionally need a .10 or even a .12 shape, if their apical canal form is large. So, the MB and DB canals will be shaped to a .06 taper and the palatal to a .08 taper, with the final apical diameters to be determined by apical gauging procedures done after the initial shape has been cut.
This tooth had two MB canals that were apically confluent. GTX shaping is done in the presence of 6% NaOCl, and the shaping routine in small canals is always begun with the 20-.06 GTX File used at 300 RPM with a torque limit of around 250 gm/cm. The 20-.06 GTX File is spun up and introduced into the canal with a light but steady apical movement. This is where the biggest difference between GT File and GTX File function becomes apparent. The GT Files, with their smaller chip space, typically cut for about 4 to 6 seconds before stalling in their apical prog-ress due to the cut debris filling those chip spaces; whereas the GTX Files (having twice the chip space) will cut for more like 10 to 12 seconds before stalling. I usually let the file continue its apical progress without any interruption. However, many of my colleagues cut with them for 3 to 4 seconds, withdraw just a half-millimeter, and then continue further apical progress until the stall.
The main issue is that landed-blade files do not cut effectively when used with an in-and-out pecking motion, they require the blades to be set against the canal walls for cutting to occur. While this is sometimes perceived as a less effective cutting event than the bite of nonlanded blades, the time to completion of shape belies that perception. Obviously, when the GTX File finally stalls, it is retrieved, the blades are cleaned with an alcohol gauze, and then it is re-introduced for further cutting. When the same GTX File starts to stall again, it is time to drop down in size to a 20-.04 GTX File so that initial shaping in small canals can continue safely. In this case, the 20-.06 GTX File cut all the way to length in the MB1 and MB2 canals in 2 or 3 cutting cycles, but in the DB canal a 20-.04 GTX File was needed to achieve length. This is typical in maxillary molars.
One of the new technique strategies taught for GTX File use is that of visual gauging at the end of initial shaping; looking at the first 20 Series GTX File that cuts to length to determine whether there is dentin debris in the tip flutes. When the first GTX to length has debris packing the last flute space, there is a good chance that the terminus is no larger than the tip diameter of that file. When that file is devoid of chips at its tip, it is most likely that the terminal diameter of the canal is larger.
This is a time saver as it eliminates the need to introduce Ni-Ti K-files (tactile gauging) to determine if a larger apical size will be needed to create apical continuity of taper—confirmation that the taper in the preparation extends all the way to the apical terminus. Apical continuity of the taper is what gives us the greatest chance of having apical accuracy when we fill the canal, so this is a critical element of the GT and GTX technique. Visual gauging allows a quick decision to be made on the likely final shape, and in this clinical case the 20-.06 GTX File had no tip debris after reaching the terminus of the MB1 and MB2 canals, indicating that a 30-.06 GTX File should then be used. In the DB canal, the first file to length (the 20-.04 size) showed tip flutes packed with debris, indicating that a 20 Series GTX File would probably suffice to complete the shape in that canal. And in fact, when the 20-.06 file was cut to length and tactile gauging was done, this proved to be the case.
This technique shows the clinician which tip size of a .02 tapered K-file binds at length, indirectly revealing the apical diameter of the canal. Tactile gauging is done with Ni-Ti K-files to increase the accuracy of the test since the more rigid stainless steel K-files can cause misreads of apical diameters. Tactile gauging is done in the presence of 17% aqueous EDTA so that the smear layer is removed at the same time that shaping is completed (in visual gauging you will still place EDTA in the canal for a minute to remove the smear layer before re-introducing NaOCl), and it is absolutely critical that the Ni-Ti gauging files are used with a straight-in, straight-out motion—not even a wiggle can occur or the apical constricture will be cut open and further shaping will be required to recreate apical continuity of taper.
Shaping of the palatal canal (a medium-size canal) was begun with a 30-.08 GTX File and it easily cut to length, showing no chips at the tip of that file. A 40-.08 GTX File was then cut to length with visual gauging indicating that shape might then be complete—a fact that was confirmed by tactile gauging. Each canal was shaped with just two GTX Files, and the post-op radiograph (Figure 2) shows very conservative coronal shapes and excellent apical accuracy in the obturation.
CASE 2 MANDIBULAR MOLAR RETREATMENT
Figure 3. Mandibular molar with failing endodontic therapy, due to apically inadequate treatment in all canals.
Figure 4. Negotiation files in mesial canals after removal of filling material and advancement through apical blockage. Note the severe curvatures.
Figure 5. Postoperative radiograph showing apical confluence of mesial canal shapes and the second apical portal of exit branching off the point of confluence. Also note the apical ledge at the curvature in the distal canal, bypassed with bent stainless steel K-files and finished with a prebent GTX Rotary File.
Figure 3 shows a previously treated tooth that was sensitive to percussion and biting pressure. It had an overt apical lesion on the mesial root apex due to the inadequacy of apical treatment. After removal of the gutta-percha, lubricant and small K-files (Lexicon C-Files [DENTSPLY Tulsa Dental Specialties]) were used to bypass the apical blockage in the mesial canals (Figure 4) and the ledge in the distal canal. The mesial canals had separate apical openings that were each negotiated. However, they were also confluent and my shaping files working through those canals cut into a common terminal opening. No worries, the second apical portal of exit in that root was kept patent with a No. 15 K-file, the gutta-percha points were fit into the confluency, and the second opening was filled during the Continuous Wave of Condensation Downpack. They were initially shaped with a single 20-.06 in 3 cutting cycles, followed by a 30-.06 GTX File to finish since the 20-.06 had no tip flute debris upon reaching length.
The distal canal was more difficult because it had a sharply bent canal with a ledge at the apex of that curve (created by the previous dentist who treated the patient). Pre-bent Stainless steel K-files were used to bypass the ledge impediment and a series of files (sizes Nos. 15 to 30) were used in a light serial step-back technique to rough out the apical shape. I had used this technique to cut tapered-preparation shapes in root canals for about 10 years, and although it was the only method we had before variably-tapered Ni-Ti shaping instruments were available, it was slow, tedious, and created less- than-perfect tapers in canals. So in this case, although it was necessary to cut an initial shape with this method, I wanted a more ideal apical taper that would improve the apical accuracy of obturation in that canal.
The technique taught to me by Dr. David Rosenberg in these situations is to prebend the Ni-Ti shaping files with an Endo-Bender (SybronEndo) pliers. While nickel titanium (even with its shape memory) is commonly thought to be impervious to bending, it actually requires greater flexure—about a 180 degree bend—to achieve a residual bend of approximately 30 to 45 degrees. This can be done to GT Hand Files or to GTX Rotary Files (I prefer using handpiece-driven files for this procedure). After a 30-.08 GTX File was bent and the directional indicator on the stop was aligned with the bend, I tapped the foot-pedal until the bend on the file in the handpiece was in a distal direction, dropped it past the ledge impediment, and hit the gas. The file quickly cut to length, the canal was tactily gauged at a No. 30 K-file size, so the shape was done!
However, the ledge was so large that it was virtually impossible to fit a gutta-percha cone beyond it, so this canal was filled with a GTX Obturator. These filling devices always move a front of sealer and gutta-percha ahead of the carrier. So, in this case I filled beyond the impediment by inserting the obturator to the ledge-point in 4 seconds, thus accelerating the apical movement of filling material ahead of the carrier by 3 to 4 mm. This was instead of the usual 6- to 8-second insertion time described in my typical GTX Obturator technique, necessary to limit the filling material to only end up 1 mm ahead of the carrier—obviously the goal when the carrier can be placed to a length 1 mm short of the terminus.
This case was shaped with just 2 GTX Files in the reasonable curvature of the mesial canals. However, as is the case with difficult canals, the distal canal required 4 K-files and a single GTX File (Figure 5).
CASES 3 AND 4 (2 OTHER CLINICIANS’ GTX TECHNIQUE CASES)
These 2 cases (Figures 6 and 7) were done by my good friend, Dr. Giuseppe Cantatore, who lives and practices in Rome, Italy. Dr. Canta-tore’s GTX technique is as follows: He negotiates each canal up to a K-file size No. 20, cuts a 20-.06 GTX File to length, then a 30-.04 GTX File to length, and finishes with a 30-.06 GTX File in virtually all canals. Giuseppe is known for his very conservative coronal shapes through which he uses carrier-based obturation to fill with stunning apical results.
The final 2 cases (Figures 8 and 9) were treated by another good friend and inspiration, Dr. David Rosenberg from Vero Beach, Florida. In his case notes, he stressed that he spent a lot of time creating ideal access cavity preparations prior to instrumentation, with special emphasis on creating straight-line glide paths for files so that they are not accumulating cyclic fatigue stresses in the coronal third. He assured me that he no longer uses Gates-Glidden Burs for that approach and instead uses ultrasonic tips and an LAX diamond bur (SybronEndo) where it fits without over-enlargement of orifices.
Dr. Rosenberg also instruments to a No. 20 K-file size in small canals before cutting GTX Files to length (more handwork than I do), but as a result he usually gets the 20-.06 GTX File to length without using a 20-.04 GTX File. If he has difficulty working a No. 20 K-file to length in a tight curved canal, he cuts shape in the coronal third with a 20-.06 GTX File and then with the No. 20 gets to length with less effort. Occasionally, he will bring in a 20-.04 GTX File when a 20-.06 GTX File resists placement. In medium or large canals, he works progressively larger K-files to length until the first one binds at length (usually a No. 30 or No. 40), and then starts cutting shape with a 30-.08 or 40-.08 respectively.
Like me, both of these clinicians use rotary files only in a single tooth before they are discarded. We know that the cost of tracking previous file use, or worse a file separation, is never worth the cost of a new file being brought into the case.
Figures 6 and 7. Maxillary molars with “S” shaped curves in the DB canals. Note the MB root structure in Figure 6 with its narrow width and remarkable curvature. No anticurvature brushing motion was needed because of the GTX File lands and their limited MFDs. These cases were filled with carrier-based obturation. (Courtesy of Dr. Giuseppe Cantatore).
Figure 8. A mandibular molar shaped with 2 GTX Files in the mesial canals and a single 30-.08 GTX File in the distal canal. Note the excellent 3-D cleaning and filling of lateral canals. (Courtesy of Dr. David Rosenberg).
|Figure 9. Maxillary molar with severe curvature in all 4 canals. Note the conservative coronal shapes, the excellent apical control, and the multiple lateral canals cleaned and filled. This is an awesome clinical result requiring only 2 GTX Files per canal. (Courtesy of Dr. David Rosenberg).|
Dr. Buchanan is a Diplomate of the American Board of Endodontics and a Fellow of both the International College of Dentists and American College of Dentists. Dentists interested in his videotape series, The Art of Endodontics, and his hands-on laboratory workshops in Santa Barbara, Calif, can call (800) 528-1590. For more information related to this article, visit endobuchanan.com for GTX updates and answers to frequently asked questions indexed by topic. A free online CE course on the GTX System is available, as well as other topics. Questions concerning challenging cases can be directed to (800) 528-1590.
Disclosure: Dr. Buchanan consults for and holds patents to the GT and GTX System of instruments manufactured and sold by DENTSPLY. He also holds patents with the System B Heat Source and is the inventor of the Continuous Wave of Condensation technique. He has no financial interest in any other company mentioned in this article.
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