May 1, 2015
by Barry H. Korzen, DDS; Pavel Cherkas, DDS
Choosing the correct instrumentation technique for any given clinical situation is a function of both the canal anatomy and the behavioral characteristics of the files being used. As clinicians, we are concerned about an instrument’s ability to shape the canal in as an ideal fashion as possible and its resistance to breakage while doing so.
A quick look at the endodontic file marketplace might lead you to believe that there is a file, a system, and a methodology for every possible combination of canal anatomy. This is not true. Firstly, it isn’t practical to change technique with every case or possibly with every canal in the same multi-rooted tooth. Secondly, limiting yourself to one system will not work either, as you cannot expect it to be the ideal treatment modality in 100 percent of your cases.
What is practical would be finding the system that works best for you in the vast majority of cases that you treat and then be prepared to modify that technique as the situation demands.
Even though single-file systems have become the vogue, the use of a technique that incorporates additional instruments, each with a specific purpose in the cleaning and shaping of the canal, will more easily permit the clinician to adapt his/her technique to the clinical situation that presents itself.
Zendo (Zendo-Online.com, Oberwil, Switzerland) has recently introduced to North America one such multi-file system, the Zenith™.
The Zenith incorporates 3 different instruments (ZSC1, ZSC2 & ZSU), each with a different flute design specific to the function intended within the canal, two for cleaning and shaping and the third, a finishing file to recapitulate (Fig. 1).
The ZSC1 is a 21 mm instrument with a six percent taper, meant for use in the coronal 2/3 of the canal and has an asymmetrical cross-section producing three cutting edges, located on three different radii: R1, R2 and R3, which, when the file rotates, results in a snake-like movement down the canal (Fig. 2).
This asymmetry creates less stress on the instrument due to the rippling movement of the file along the canal walls which eliminates the screwing-in effect felt with some instruments, reduces the risk of file breakage and allows for an increased ability to negotiate canal curvatures. As well, the large helical groove created by this flute design increases the available volume for coronal debris elimination, which in turn helps to avoid the extrusion of debris beyond the instrument tip and apical foramen (Fig. 3).
The second instrument used, the ZSC2, has a symmetrical cross-section and a four precent taper and is used to complete the shaping of the canal. The use of a symmetrical file with a smaller taper at this stage of treatment insures the maintenance of the original canal configuration by the instrument being guided down the canal due to a balance of forces, and therefore, no zipping (Fig. 4).
Once the canal has been shaped to its full working length, the final instrument in the series, the ZSU, is used for canal recapitulation. It has an asymmetrical cross-section for all the reasons mentioned above and a six percent taper to allow for an improved flow of the irrigating solution in the canal and to facilitate obturation (Fig. 5).
When the canal anatomy calls for a larger apical preparation than the size 25 prepared with the ZSU, there are a series of apical shaping files, uniquely designed to retain the prepared canal morphology while shaping the orifice to either a size 30, 35 or 40. This is accomplished by the files’ apical 5 mm having a six percent taper with the balance of the fluted portion of the instrument having a zero percent taper (Fig. 6).
Lower first molar. The pre-operative radiograph shows a radiolucent area mid-root on the distal aspect of the mesial roots. The Zenith protocol allows for shaping the canal to promote improved flow of the irrigating solution without excessively enlarging the canal while facilitating obturation that allows for the movement of sealer into lateral canals and apical deltas (Fig. 7).
Lower first molar demonstrating the maintenance of the canal morphology (long and narrow) while still allowing for excellent obturation (Fig. 8).
All cases cannot be treated using a single instrument or a single technique, but the vast majority of cases can be instrumented with a simplified system that can be adjusted when necessary. OH
Disclaimer: Barry H. Korzen has a financial interest in Zendo.
Barry H. Korzen is a graduate of the University of Toronto Faculty of Dentistry and the Harvard University graduate Endodontic program. Dr. Korzen is the Founder of The Endo Academy
(www.TheEndoAcademy.com) and Zendo (www.Zendo-Online.com). He was an Associate Professor, Assistant Dean and former Head of the Discipline of Endodontics at the University of Toronto Faculty of Dentistry.
Dr. Pavel Cherkas is an Assistant Professor of Endodontics and Oral Physiology at the University of Toronto and an active member of Dr. Barry Sessle’s laboratory, where he continues to conduct research on the central mechanisms of orofacial pain. He has lectured nationally and internationally on topics related to his expertise and published extensively in peer-reviewed journals and textbook chapters. Dr. Cherkas also maintains his private practice limited to endodontics in Toronto. More information is available on EndoArt.ca.
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