In my March 2019 column, we discussed the rationale and the steps associated with performing a root canal procedure. To recap the article, we looked at how certain endodontically diseased teeth may be best treated by root canal therapy, rather than extraction due to the invasiveness of removing functionally important teeth in dogs and cats. Then we discussed the steps associated with standard (orthograde) root canal therapy, including access, instrumenting the canal (cleaning and shaping), obturation, and restoration.1,2 Let’s delve further into what many consider to be the most important step of the orthograde root canal procedure: instrumenting the canal.
I recently had a conversation with my cousin, Brian D. Hall, DDS, who is an endodontist for humans in Frederick, Md. In addition to having a unique dentist’s office (and one that emphasizes the soothing effects of music), Brian has a passion for cutting-edge techniques and equipment in endodontics. Since many veterinary dentists are utilizing rotary and reciprocating file technology, I wanted to get Brian’s input on how its use has affected his practice.
Step-back versus crown-down
Brian attended the University of Maryland Dental School from 1993 to 1997, and then performed his endodontic residency from 1997 to 1999. During his time in dental school, he learned traditional hand-filing methods, such as the “step-back” technique. This approach uses a small file to advance to the apical portion of the root canal, followed by sequentially larger files that will clean and shape the apical third of the canal. This is followed by various flaring techniques of the coronal portion of the canal to facilitate irrigation and obturation.3 The step-back technique is in contrast to the “crown-down” technique, where the coronal portion of the canal is widened by inserting wide files that don’t even come close to reaching the apex, but help to widen the coronal root canal at the beginning of the procedure to improve access to the apical portion of the canal. Using hand files is arduous and time-consuming for either of these shaping techniques, especially in small canals.
During his residency, Brian learned how to use rotary and reciprocating endodontic systems. He tells me this technology has been a game changer for the specialty of human endodontics, and I’d have to agree the same is true regarding our veterinary endodontic patients. Rotary files are attached to a motorized handpiece that allows RPM, and in some cases, torque settings to be customized. Other features are often built-in, such as an auto-reverse function for the file to minimize breakage when one binds. These rotary systems are coupled to nickel-titanium (Ni-Ti) files that are very flexible to decrease the likelihood of file breakage. These files are made in lengths that can reach the apex in even the long, curved canine teeth of dogs (Figure 1).
In contrast to rotary systems that spin in full rotations either clockwise or counterclockwise, reciprocating systems rotate in one direction and then switch directions. Though reciprocating and rotary motions may have similar cutting efficiency, reciprocating motions extend the lifespan of files tested.4 These reciprocating movements may be symmetrical in their clockwise and counterclockwise movements (oscillation), but they are often asymmetrical, meaning the clockwise rotational movement may be 30 degrees, followed by a counterclockwise movement that may be greater than 30 degrees.
The efficiency gained by mechanized filing systems has revolutionized how root canal therapy is done. In fact, some systems allow for a single reciprocating file to clean and shape the entire canal. In veterinary dentistry, root canal therapy is typically not staged over two visits since general anesthesia is necessary. However, in human endodontics, it was common for the root canal procedure to be staged over two visits. Now, due to advances in instrumentation, Brian tells me he can typically finish approximately 80 percent of his patients’ root canal treatments in a single visit, requiring 20 percent of patients to return only if they have a particularly challenging canal or bleeding into the canal from the apical vessels.
One of the rarely discussed benefits of mechanized Ni-Ti instrumentation in our veterinary patients is seen in the most commonly treated teeth, namely fractured canine teeth with pulp exposure. In the past, when using veterinary-length hand files, a separate access site through the crown near the gingival margin was necessary to allow for straight-line access to the apex. Now, with the flexibility and length of the Ni-Ti rotary/reciprocating files, in most cases, less tooth structure can be removed by instrumenting through the site of pulp exposure. Removing less tooth structure may help to decrease likelihood of repeat fracture of the endodontically treated tooth.
John Lewis, VMD, FAVD, DAVDC, practices dentistry and oral surgery at Veterinary Dentistry Specialists and is the founder of Silo Academy Education Center, both located in Chadds Ford, Pa.
1 Miller BM, Lewis JR. Veterinary dentistry. In: Bassert JM. McCurnin’s Clinical Textbook for Veterinary Technicians, 9th ed. Elsevier; 2018: 1336-1339.
2 Lewis, JR. Getting to the bottom of root canal therapy. bit.ly/32kZpgI
3 Peters OA, Peters CI. Cleaning and shaping the root canal system. In: Cohen S, Hargreaves KM. Pathways of the Pulp, 9th ed. Mosby Elsevier, 2006: 290-357.
4 Grande NM, Plotino G, Ahmed HMA, Cohen S, Bukiet F. The reciprocating movement in endodontics. Endodontic Practice. bit.ly/2PKSPgF