Do You Know What Your Endodontic Instrument Just Did?

Transcription

1 Volume 33 No. 2 Page 118 Do You Know What Your Endodontic Instrument Just Did? Authored by L. Stephen Buchanan, DDS Upon successful completion of this CE activity 2 CE credit hours will be awarded Opinions expressed by CE authors are their own and may not reflect those of Dentistry Today. Mention of specific product names does not infer endorsement by Dentistry Today. Information contained in CE articles and courses is not a substitute for sound clinical judgment and accepted standards of care. Participants are urged to contact their state dental boards for continuing education requirements.

2 Do You Know What Your Endodontic Instrument Just Did? Effective Date: 2/1/2014 Expiration Date: 2/1/2017 ABOUT THE AUTHOR Dr. Buchanan is a Diplomate of the American Board of Endodontists, Fel low of both the American and International Colleges of Dentists, as well as part-time faculty at Uni versity of California at Los Angeles and University of Southern Cali - fornia endodontic residency programs. He treats patients and trains dentists in Santa Barbara, Calif. He can be reached at (800) , at info@endobuchanan.com, or by visiting the Web site delendo.com. Disclosure: Dr. Buchanan holds licensed patents and consults for the following endodontic instruments and companies: System-B at Axis Sy bronendo, GT Files, GTX Files at DENTSPLY Tulsa Dental Specialties. WORRYING ABOUT THE WRONG THING One of my childhood memories is my mother Donna repeatedly telling me, Steve, you re worrying about the wrong thing, and she was usually right. So has it been in the specialty of endodontics the best example being our misplaced fear of overfills. I am not saying overfills signify procedural brilliance; rather, it is that surplus filling material has been the wrong thing to worry about. From 1950 through the 1970s, more than 60 research studies investigated the connection between the apical extent of obturation and the incidence of root canal therapy (RCT) failure, and the vast majority got it wrong, greatly misdirecting the new ly reborn specialty. How did this happen? Like most other mysteries of endo, it oc curred because of the obscure nature of en dodontic anatomy. To understand this better, follow me through a short history of RCT overlaid upon the misdirection of the apical stop preparation technique and its obscure but devastating clinical results. We re in the 1950s, 60s, or 70s, and we ve just pulled Figure 1. One month post-op radiograph showing enlarging periapical lucency after disastrous transportation during rotary shaping with the most flexible but nonlanded file on the market. our endodontic chestnuts out of the flames of the focal infection era (FIE). Finally, it s okay to save our patients endo dontically diseased teeth if we can show a negative culture from instrumented canals. (I know, very funny considering what we know now about anaerobic culturing, DNA identification, and biofilm. Anyway, back to the story.) Before the infanticide of endo, we had a rich history of mechanical and chemical de velopment in the field. We knew how to use effective irrigation protocols (sulpheric acid, sodium hypochlorite [NaOCl], and ethylenediaminetetraacetic acid [EDTA]), we used iontophoresis to impregnate dentin with iodine (remarkably effective), and we cut tapered shapes and filled 3 dimensionally with chloropercha obturation methods. After FIE, not so much. We came back from the abyss with the apical stop preparation essentially an intentional ledge near the end of the canal the ubiquitous shaping objective during that time, so let s dissect how that preparation objective plays out clinically. Near the end of a canal it s called a stop, which is good thing; when the same shape has been cut into the body of a curved canal, we call it a ledge, which is a bad thing. Ledges are bad because they are difficult to instrument beyond and are often impossible to fill beyond. So how does one overextend a gutta-percha cone beyond an intentional ledge prep cut short of its end within the root canal? In fact, it is impossible to overfill a well done apical stop prep, if traditional conefit and filling methods are used. Put a different way: any overfilled canal that had a stop prep cut into its terminal region was almost certainly munged during shaping, than a conefit or condensation failure (Figure 1). As we better understand now, even slightly curved 1

3 canals will be straightened, thus shortened, during shaping procedures. When canal length shortens during shaping procedures, files that were intended to cut an intentional ledge inside root structure will inadvertently cut beyond the terminus of the canal the previous stop position is now outside the root and there is no apical resistance form at best. At worst, the ends of curved canals have been ripped open by the transportation that inevitably occurs when large instruments are cut long. With that in mind, consider the RCT done at that time with the stop prep as objective. Nearly all of the research studies that looked at the correlation of overfills to RCT failures showed a higher incidence of failure when overfills were evident. I m good with that observation; I m not good about the latter part of the discussions and definitely not good about conclusions that got the most important point wrong the vast majority of investigators pointed to surplus material as the etiology for the failure. So how does that work? How does a relatively biocompatible material like gutta-percha encourage persistent infection and inflammation when it flies out the end of root canals? The answer is that it doesn t; surplus filling material has never been the etiology for RCT failure; instead, it was coincidental to the true etiology the apical derangement that preceded the fill. You can make fun of our predecessors, but this fundamental misunderstanding continues today, despite the advantages gained by using Ni-Ti rotary files. Clinicians today are still misdirected in their concerns about what could go wrong during RCT procedures, just in a different way. Now we worry about file breakage, when we should be much more worried about poor shaping outcomes (Figure 2). WHAT CAN GO WRONG WITH A CUTTING TOOL IN A ROOT CANAL? That would be breakage, blockage, ledging, apical perforation, coronal overenlargement, and lateral perforation, just to mention a few. Of all these untoward outcomes, the sins of overcutting are the worst because they are irreversible, and because failures that result from cutting errors in the apical third are the most difficult to retreat nonsurgically. Remarkably, file breakage is more feared. Figure 2. Computed tomography reconstruction of adjacent canals after preparation with landed and nonlanded rotary files (left and right, respectively). Note the shape cut with a landed GTX File is true to the original canal path, while the shape cut with a nonlanded rotary file has ripped the terminal canal path set up for an overfill, possibly a mysterious failure. Overcut coronal shapes irreversibly reduce the structural integrity of teeth, just as overcut apical preps inevitably cause lacerations that require retrograde surgery to repair. On the other hand, separated root canal files rarely reduce the prognosis for the tooth; at worst they require an additional procedure to remove the file segment or place a retro seal beyond it, while the majority of separated file cases need no further treatment. Why this misallocation of fear when we operate cutting instruments? My take on this cognitive dissonance is that file breakage is more feared by dentists because we are immediately accountable when an instrument comes apart in a root canal. Right then, when a file disarticulates, we must tell the patient before he or she leaves, or risk malpractice liability. Conversely, when the end of a root canal is devastated by careless use of dangerous files, it may take 6 to 24 months for the subsequent failure to present in radiographic or symptomatic form, and, by then, it s just another one of those mysterious endo failures. Phrases like cracked root and endo doesn t work that well get bruited about. A great deal of this apical damage is caused by nonlanded rotary files, with tip diameters larger than 0.20 mm. If this is so, why are nonlanded, rapid cutting files so popular? My best guess follows: When I review what was going on just before my last rotary file separation, the file I had in the canal was laboring, it was making grudging apical progress, I kept it in there too 2

4 long, or worse, I gave it a bit of a push and tink separation. My theory is that when dentists try a new, razor-blade-sharp rotary file, and every larger file cuts to length without labor, I think most of us feel comforted by that effortless cutting experience. No labor means no breakage, right? The problem with this sunny scenario is that when increasingly larger nonlanded files cut easily to length in small curved molar canals, they seldom cut along the original apical canal path, transporting and/or ripping the apical foramen open, followed by the inevitable and mysterious overfill. My partner Jack Sturm is an exceptional endodontist, and his apical accuracy is usually dead-on. I resent it a little bit, but his fills are more tightly controlled than mine. The only time I ever saw him overfill in a dramatic way was after he began using ProTaper F2 and F3 (DENT SPLY Tulsa Dental Special ties) to finish small canal preps in molars; an outcome quickly eliminated after saying adios to the ProTaper F2 and F3, and going back to finishing small canal preparations with landed rotary files. I will admit to experiencing a bit of schadenfreude about Jack sailing a gutta-percha cone or 2 out the terminus (like the rest of us mere mortals), but what I saw in his next move, for the first time, was cooler than I understood at the time. He morphed his shaping technique to what has since become known as the hybrid shaping technique a technique using ra pid cutting files in small sizes to do the initial opening of a small curved canal, followed by slower-cutting, radial-landed files to safely carry the taper to the terminus. Years of clinical experience by thousands of progressive en dodontists worldwide have proven this to be one of the most efficient and effective shaping methods in use today. Why does this work so well? Hybrid Shaping Concepts Understanding the functional characteristics of different file features (blade geometry) is a challenging problem requiring consideration of how each of these features work together in dynamic motion, how they function in different sizes, and how they cut in different anatomic forms. In other words, it s complicated. Change one file feature to im prove a certain aspect of file function and know that some other behavior will change as well. Make file blades too dull (ie, when land widths are excessive) and the file will never cause apical transportation, but it will need too much time to cut the desired shape, and cyclic fatigue breakage is inevitable. Make the flutes too sharp, and breakage will be less of a concern, but derangement of fragile apical anatomy will occur an outcome far worse than file breakage. The a-ha moment for me, considering sharp versus landed flute designs, was when I finally deconstructed in my mind why the Pro Taper S1, S2, and F1 files are safe and efficient, and why the F2 and larger sizes are not safe in rotary cutting mode. All of these files have the same crosssectional flute geometry, but the functional behavior is seen to change between 0.2 mm (F1) and 0.25 mm (F2) tip diameters. Why? Transportation of curved canal paths requires 2 separate conditions to exist for apical damage to be done: the file must have sharp cutting flutes and it must be stiff. If we could make an infinitely flexible file, it could be razor-blade-sharp without fear of transportation occurring. In the real world, Ni-Ti rotary files, even those with radial lands, become stiff and dangerous in larger than a size No. 20 tip diameter. The heart of the hybrid-shaping concept is to use sharpbladed rotary files in small sizes to cut initial shape, then finish with landed rotary files. If sharp-bladed files of larger tip diameters are preferred, I recommend using them in a reciprocating handpiece. Reciprocation has become fashionable recently, its advantage being avoidance of apical transportation with nonlanded files in larger sizes. It originally became popular because reciprocation was found to be a safer file motion for use with nonlanded ProTaper F2 Files. While it is an improvement over using stiff, nonlanded files with a rotary cutting motion, reciprocation takes significantly longer than hy brid rotary techniques, it requires a special handpiece, and it necessitates more frequent removal of files to clean the flute spaces or cut debris will be forced apically. You don t need a $45 single-use shaping file and a new handpiece to cut ideal shapes safely and rapidly. Pick the right initial enlargement file, and you may be able to negotiate and shape small curved canals in less than a minute using no hand files; rather, just 2 to 3 rotary files. 3

5 Choosing and Using a Hybrid File Set DENTSPLY Tulsa Dental Spe - cialties introduced what I consider the ideal rotary file ( Vortex Blue [VB] Rotary File) to begin a hybrid shaping technique. I initially experienced this file while doing my best to destroy it in a severely curved mesial root of an extracted lower molar. I had finished all of my demonstrations on the second day of one of our hands-on courses and all 14 course participants were beavering away, hoping that I would stay out of their hair so they could finish the cases they were working on. That is when I saw a package of these instruments, sent by Dan Ammon (Tulsa s head of Research and Development) on my lab bench. I did my initial testing in a very mean way by using a rotary file technique in a manner most likely to separate a small Ni-Ti rotary file, jamming it into a small, dry, curved canal in the tooth mentioned above, and it rapidly cut to a binding point. I removed the file, cleaned the flute spaces with an alcoholsoaked 2-x-2 gauze, and continued to jam it repeatedly into this nightmare canal, ringing the torque limit alarm set at 300 Ncm, and sud denly, after 4 cutting cycles, it had cut to length! Obviously a fluke, I said to myself. I ll break it in the adjacent curved canal. It cut to length in that canal as well! With no small hand pressure, I used that same file in 15 more small molar canals to the same result, except in one canal that had an impediment (easily negotiated around by hand with prebent SS hand K-files [DENT SPLY Tulsa Den tal Specialties]). This is the file I am using to initially enter small orifices and canals, and I let it cut to length if it continues to easily advance, cleaning the file every 3 to 4 cutting cycles. Any time the file meets resistance twice at the same point in the canal, it is immediately replaced with an 08 K-file; straight at first, then the same file that has been smoothly but sharply bent, in preparation for finding a path to traverse past the impediment. Never bang on an impediment with any kind of Figure 3. The dynamic duo: left, a Vortex Blue (VB) Rotary File (DENTSPLY Tulsa Dental Specialties); right, a GTX File (DENTSPLY Tulsa Dental Specialties). Note the sharp blade but tiny tip diameter on the VB File, and the flattened flute edge (radial-land) on the GTX. Most small molar canals in my practice are fully negotiated and shaped with just these 2 instruments. Figure 4. Spiral ZFile, the first coiled rotary file. The s-shaped block canal was cut to this result in less than 7 seconds. file hand, rotary, or otherwise. During this initial negotiation and shaping action, the rotary VB and hand K-files work through lubricant that fills the access cavity. In the cases where this initial rotary file stalls short of length, hand K-files will easily drop to length, 08, 10, 15, as all coronal ob struction has been cut away with the VB, even though the VB file didn t cut to length. Once a 15 K-file has been worked to length, the VB file will cut there as well, barring tortuous canal curves. Use an apex locator to find the end of the root canal, blipping the foot pedal for the handpiece to move the rotary file up and down to the position indicated by the electronic apex locator. Gauge with Ni-Ti K-files to see which tip size binds at length, then choose a GTX File (DENTSPLY Tulsa Dental Specialties) with the same tip size, and cut it to length, and finito! Instead of 3 hand files, and one or 2 shaping files, this method usually requires just a single razor-like rotary file for initial negotiation and shape, followed by a single radial-landed rotary file to cut final shape 2 files! And they each cost less than $10 (Figure 3). This is the best technique and productivity advance I have seen in several years. 4

6 ECCENTRIC AND SPIRAL SHAPING FILES: HOW DO THESE WORK? The latest new file on the market is the ProTaper Next (DENTSPLY Tulsa Dental Specialties), a Ni-Ti shaping file with a different twist: it has an eccentric core, relative to the long axis of the file. When looking at conventional rotary files in successive cross sections, the square or triangular core rotates around the long axis of the file as it narrows, creating the helical paths of the cutting flutes. ProTaper Next Files look, in cross section, as if a square file had one side ground a bit, making the remaining cross section slightly rectangular. In successive cross-sectional views, this shape rotates eccentrically down the same outside flute path as when it was a square file. The gift of this file comes primarily from having a larger chip space between cutting flutes than any other 4-sided file, no small accomplishment. Also, compared to a square cross section rotary file, this rectangular cross section delivers a more flexible instrument. These in struments seriously outperform all reciprocating instruments. Beyond eccentric cross sections, the next file innovation in this vein is called ZFile (Figure 4). Designed by Dr. John McSpadden and Mr. Mark Ferber, ZFile geometry has taken eccentricity to an extent that is better described as a coiled, or spiral shaping file, and it is distinguished by having a space along its centerline. This instrument, in testing by the author, cut to length in most small, curved molar root canals in a single 5- to 8-second cutting cycle (Figure 5). Initial and consequent trials delivered shaping outcomes that were faster and truer than any file I ve ever used, from a file so remarkably different in its form and behavior that it was difficult for me to deconstruct its effectiveness, until I considered the effect of filled chip spaces, the greatest difference between it and conventional rotary file designs. ZFiles ribbon-shaped, cross-sectional geometry delivers great flexibility, slow accumulation of cyclic fatigue, and the largest chip space since the SAF file. This enormous chip space typically allows cutting to length in a single cycle as the Figure 5. Post-op radiograph of the first clinical case shaped with a single ZFile. All 3 canals were shaped with the same Rotary ZFile; 4 to 6 seconds to shape each canal, the distal terminus gauged at 0.35 mm, so the ZFile was cut 2.0 mm long in that canal. Note the lack of transportation despite the overextension of the cutting instrument. Also note the multiple lateral canals filled, testament to the enormous chip space afforded by this file. flute spaces can carry the whole amount of debris cut out of a small canal to create final shape. When that possibility occurred to me, I back-checked my theory by changing my current shaping routine to see what happened hopefully I would see more lateral canals filled, as I did with ZFile. It s All About Chip Space and Laterally Burnished Debris ZFile taught me that debris-filled chip spaces are a greater problem in rotary instrumentation than I ever understood before using this instrument. I changed my shaping irrigant of choice from 6% NaOCl to 17% EDTA (NaOCl after shaping is completed), removed and cleaned my shaping file more often as I ap proached final length, and the results have been dramatic. The frequency of lateral anatomy I have seen with my current hybrid technique of VB and GTX Files, along with my new irrigation protocol, has roughly doubled. My course participants have had the same experience. CLOSING COMMENTS The next time you perform RCT, ask yourself if you really know what your instruments just did. If you re not sure, or if you d just like to shave minutes off your shaping times, give this VB/GTX hybrid ro tary shaping technique and the EDTAduring-shaping irri gation technique a try, and let me know how it goes. 5

7 POST EXAMINATION INFORMATION To receive continuing education credit for participation in this educational activity you must complete the program post examination and answer 6 out of 8 questions correctly. Traditional Completion Option: You may fax or mail your answers with payment to Dentistry Today (see Traditional Completion Information on following page). All information requested must be provided in order to process the program for credit. Be sure to complete your Payment, Personal Certification Information, Answers, and Evaluation forms. Your exam will be graded within 72 hours of receipt. Upon successful completion of the postexam (answer 6 out of 8 questions correctly), a letter of completion will be mailed to the address provided. Online Completion Option: Use this page to review the questions and mark your answers. Return to dentalcetoday.com and sign in. If you have not previously purchased the program, select it from the Online Courses listing and complete the online purchase process. Once purchased the program will be added to your User History page where a Take Exam link will be provided directly across from the program title. Select the Take Exam link, complete all the program questions and Submit your answers. An immediate grade report will be provided. Upon receiving a passing grade, complete the online evaluation form. Upon submitting the form, your Letter of Completion will be provided immediately for printing. General Program Information: Online users may log in to dentalcetoday.com any time in the future to access previously purchased programs and view or print letters of completion and results. This CE activity was not developed in accordance with AGD PACE or ADA CERP standards. CEUs for this activity will not be accepted by the AGD for MAGD/FAGD credit. POST EXAMINATION QUESTIONS 1. Ledges are bad because they are difficult to instrument beyond and are often impossible to fill beyond. 2. Nearly all of the research studies that looked at the correlation of overfills to root canal therapy (RCT) failures showed a higher incidence of failure when overfills were evident. 3. Overcut coronal shapes irreversibly reduce the structural integrity of teeth, just as overcut apical preps inevitably cause lacerations that require retrograde surgery to repair. 4. Transportation of curved canal paths requires 2 separate conditions to exist for apical damage to be done: the file must have sharp cutting flutes and it must be very flexible. 5. The heart of the hybrid shaping concept is to use sharp-bladed rotary files in small sizes to cut initial shape, then finish with landed rotary files. 6. The latest new file on the market is the ProTaper Next, a Ni-Ti shaping file with a different twist; it has an eccentric core, relative to the long axis of the file 7. ProTaper Next Files look, in cross-section, as if a square file had one side ground a bit, making the remaining cross-section slightly rectangular. The gift of this file comes primarily from having a larger chip space between cutting flutes than any other foursided file, no small accomplishment. 8. ZFile s s ribbon-shaped cross-sectional geometry delivers great flexibility, and slow accumulation of cyclic fatigue. One drawback is that is has the smallest chip space since the SAF file. 6

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