Last Act With A File

Conefitting is tricky, but it is necessary for the efficient obturation of the root canal system. Dr. L. Stephen Buchanan discusses a method that will help make the process more successful.

Root canals systems can be microscopic tortuous pathways, and below the orifice, their anatomy is obscure at best. Because of this, endodontists, have taken many wrong turns on the lonely way to the apex. The difficulties of conefitting are a great example.

Conefitting is a common challenge in RCT (one of the main drivers of early Thermafil® acceptance by the GP community), and most clinicians think it is because apical regions of canals are so small that gutta-percha cones have trouble traversing to length. Au contraire. While the last three millimeters of the apical region is very small, current manufacturing standards mean that we can easily fit cones into canal shapes smaller than 15-.03 when the canal is unobstructed by debris. The problem is that after instrumentation, canals are always obstructed by debris, albeit a very tiny bit of debris when it’s done carefully. It requires mental imaging skills to understand the huge impact of this miniscule impediment, but it is contained in a very tiny space, and as such, it constitutes a soft tissue blockage of sorts.

You might think that this debris can be pushed aside or out the end of the canal with the master cone, but fitting gutta-percha points is like trying to push a noodle up a pipe, so any slight irregularity in a canal wall or crust left near the terminus will make it an impossible procedure. This lack of patency is the culprit in 99% of all conefitting difficulties, yet academics continue to debate whether the use of patency instruments is safe. That is nonsensical to me.

Ironically, even some of those clinicians who understand the safety and importance of patency procedures endure conefitting frustration when their final patency procedures are done in the presence of NaOCl. NaOCl is essential for disinfection and dissolution of pulp tissue remnants, but it does nothing to hard tissue particles, so the debris remains clumped near the terminus.

When an acidic irrigant like EDTA is used during patency procedures instead of bleach, these mineralized particles melt into solution, and after that, the same exact GP cone that could not be coached to length drops there immediately, delivering perfectly crisp tugback. Remember, the slightest scrape of a file on a canal wall, even gauging, recreates a smear layer that must be removed again before obturation. I call this procedural concept, “Last Act With A File” (LAWAF), and with my nerd in full bloom, I say it to myself as a mantra after completing instrumentation of all canals. “Irrigate with EDTA, slip a file to and through the terminus of the canal, and the GP fits to length.” The solution is super simple and works every time.

In 1975, McComb and Smith recommended that dentists do all instrumentation with 17% EDTA. In 1987, Baumgartner confirmed the basis for that recommendation, and in 2002, Ralan Wong showed the problem to be hugely magnified by the use of rotary files. When using rotary files, the ground dentin and pulp debris created is not a layer; it fills the entire canal and any adjacent lateral recesses in 1.5 seconds. Most of us continued to apply Schilder’s irrigation concepts despite the fact that all the tools have changed, creating vastly different dynamics between our instruments and our irrigants. Should we worry about carrying EDTA through the ends of canals with patency files? Re-engage your mental imaging powers, and you will see that patency files displace irrigants from apical regions; they don’t carry aqueous solutions anywhere.

Remember, instrument with EDTA, use the LAWAF procedure to finish, irrigate effectively with NaOCl, stuff that root canal system, and I’ll see you at the apex.

Read more about the challenges of irrigating and conefitting in Dr. Buchanan’s article, “Anatomy of a minimally invasive endodontic case,” here:

Stephen Buchanan, DDS, FICD, FACD, Dipl. ABE, has been lecturing and teaching hands-on endodontic continuing education courses for over 30 years, both in his state-of-the-art training facility in Santa Barbara, California, as well as in dental schools and at meetings around the world. He currently serves as a part-time faculty member in the endodontic departments at the University of the Pacific’s Arthur Dugoni School of Dentistry and the University of California at Los Angeles as well as being the Endodontic Advisory Board Member to the Academy of General Dentistry. He is a Diplomate of the American Board of Endodontists and a Fellow of the International and American College of Dentists. Dr. Buchanan also maintains a private practice limited to Endodontics in Santa Barbara, California.

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