Simplify Challenging Endo Cases With the K3™ Rotary File System By Frederic Barnett, DMD & Kenneth S. Serota, DDS, MMSc

Abstract
Nickel-Titanium rotary instruments have simplified the endodontic treatment of teeth with moderate to severe canal curvatures. However, exceeding their torque limits or inappropriate usage may result in sudden file breakage or canal transportation. These iatrogenic complications may have a negative influence on the successful outcome of treatment. Therefore, instruments with a higher degree of fracture resistance as well as safer procedural protocols are warranted. This case report discusses the clinical use of a 3rd generation NiTi file rotary system that incorporates computer-assisted design characteristics for increased safety and effectiveness. Their clinical use in a maxillary second molar with four canals is described in a step-by-step approach.

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The super-elasticity and self-centering features of Nickel-Titanium (NiTi) endodontic files has made it possible to instrument moderately and severely curved root canals with relative ease and safety as compared to traditional stainless-steel files. However, exceeding their torque limits or inappropriate usage may result in sudden file breakage or canal transportation. These iatrogenic complications may have a negative influence on the successful outcome of treatment. Therefore, instruments with a higher degree of fracture resistance as well as safer procedural protocols are warranted. Computer-assisted innovations in file design in conjunction with sophisticated technique protocols enables safe and predictable clinical results.

Innovations of Third Generation Design
A new and innovative third-generation NiTi rotary system, the K3™ (SybronEndo) was recently introduced to the dental marketplace. The K3 system is comprised of two NiTi rotary orifice-openers (.08 and .10 taper) and a full set of ISO-sized NiTi rotary files, sizes #15 through 60, in .04 and .06 tapers. A series of .02 tapered K3 NiTi rotary files are soon to be launched. The characteristics and features of the K3 system are:

Non-cutting tip – Minimizes ledging and transportation (Fig. 1).

Fig. 1: K3 file non-cutting tip, SEM.

Rake Angle – The K3 has a slightly positive angle that maximizes cutting efficiency (Fig. 2).

Fig. 2: Diagram of K3 file, cross-section.

Radial Lands – The K3 design minimizes resistance while maximizing strength to reduce the possibility of fracture (Fig. 2).

Helical Flute Angle – The K3 design has variable helical flute angles that improve the cutting performance and removal of debris.

Clinical Guidelines for K3 System:
The authors recommend the use of the Quantec ETM™–electric torque-control motor (Sybron Dental Specialties) that features an auto-reverse capability. When a pre-determined level of resistance is encountered, this motor will switch into auto-reverse mode, rotating the file in a counter-clockwise direction. This will free the file from the encountered resistance. The torque-control feedback feature compensates for localized stresses that are placed upon the rotating files and protects instruments from breakage through fatigue or sudden increases in torque. Rotating NiTi instruments are to be used with a slight pecking or “engage-disengage” motion, to minimize strain concentration. Care must be taken not to force the rotating file into the canal; once increased resistance is encountered, the current file should be immediately replaced with another of smaller taper and/or tip diameter. This protocol will greatly reduce the incidence of file breakage.

It is prudent to limit the amount of file engagement within the confines of the root canal space. Ideally, a maximum of no more than 6mm of file engagement should occur within the canal to minimize excessive torque and instrument fracture. Copious irrigation is mandatory as well as a “wet-field” instrumentation technique; never instrument dry canals!

Treatment Sequence; a Step-by-Step Approach
A 75-year-old female was referred for endodontic treatment associated with a cariously exposed posterior abutment tooth, #15 (Fig. 3). After taking a thorough medical history including blood pressure measurement, a clinical examination of the upper-left quadrant was performed. The need for endodontic treatment prior to the fabrication of a permanent fixed bridge was readily apparent.

Fig. 3: Pre-operative radiograph, tooth #15.

Straight-line access
After local anesthesia delivery and placement of the rubber dam, a Class I inlay-style access cavity was prepared to create a straight-line approach to the root canals. Four canal orifices were found upon exploration of the floor of the pulp chamber (MB, MB2, DB and Pal). The use of a dental microscope (Global Surgical) with its enhanced magnification and illumination facilitated the discovery of the MB2 orifice (Fig. 4).

Fig. 4: Dr. Barnett demonstrates
the use of a dental microscope.

Canal Exploration, Surveying and Scouting
Stainless steel (SS) .02 taper hand files were then used to confirm coronal patency by a passive assessment of the root canal anatomy; sizes #08 through #15 in sequence. After rinsing the chamber with NaOCl, the hand files were sequentially inserted into the canal using a gentle watch-winding motion until resistance was encountered; no push-pull motion was used. When resistance was felt, the file was then pulled vertically from the canal. No attempt was made to reach the working length at this time; it is unnecessary and perhaps rife with complication. The initial files need only go to one-third or one-half the projected working length. Obstructions and restrictive cervical dentin were removed during this phase.

Radicular access
The K3 orifice openers (the K3 #25/.10 and K3 #25/.08 taper) were then used to create a smooth glide path into the apical half of the root canals. The .10mm/mm tapered K3 orifice opener was used at 300rpm in the Quantec-ETM motor and brought into the canal until resistance was felt. The instrument was backed out slightly and redirected apically until resistance was again encountered. The canal was copiously irrigated with NaOCl and this procedure was repeated with the K3/.08 tapered orifice opener. This instrument should be able to penetrate to mid-root in most canals. A Gates™ Glidden #4 drill was used to widen and counter-sink all four canal orifices. The canals were then copiously irrigated with NaOCl.

Working length determination
After irrigation with NaOCl and light drying with paper points, the working length (WL) was determined. The use of an electronic apex locator, the AFA Apex Finder™ (SybronEndo) significantly facilitated the accuracy of the WL determination. Using a #10 or #15 SS hand file, a small diameter bend was placed at the tip using the Endo-Bender™ (Sybron Dental Specialties). This file, attached to the AFA Apex Finder™ was then brought to the WL using a gentle watch-winding motion, exploring for the presence of apical bifurcations and/or curvatures that cannot be readily identified in the radiographs. A properly angulated radiograph should then be taken.

Presumptive Apical Gauging
An arbitrary final apical size was estimated from the pre-operative radiographs and the fit of the #10 SS hand file. The concept was to begin with a K3 rotary file that is three to four sizes larger than the projected final apical size. For example, if the apical size was gauged at size #25, then begin the crown-down with a #40 K3. Definitive apical gauging will occur after deep body shaping of the canals.

Canal Instrumentation Using the “Variable Taper Sequence”
A combination of .06 and .04 tapered K3 NiTi rotary files were used in a crown-down sequence. The “variable tapered sequence” that was used in this case consisted of the following K3 files: #45/.04, #40/.06, #35/.04, #30/.06, #25/.04, #20/.06. These files were used with minimal force in a light pecking or “engage-disengage” fashion.

That is, they were brought apically until resistance was felt, then backed out slightly, and then advanced apically again until resistance. No more than 5-7 seconds of use per file in any canal. Then, the next rotary file in the sequence was used. This sequence was followed until the WL was reached. Canals that were initially calcified or composed of a harder quality dentin may require this sequence of K3 files to be repeated. This was the case for the MB and MB2 canals, as they were quite narrow. A #10 SS hand-file was also used between each of the above steps to ensure canal patency and prevent blockages.

Apical finishing
Once the K3 files have reached the determined working length, the clinician will need to determine the appropriate degree of apical enlargement for each canal. Final apical gauging was accomplished with a series of stainless steel hand files. If, for example, the final apical gauging procedure allows for a size #35 hand file to be placed to the WL, it may be prudent to take the #35/.04 K3 rotary file to length. The MB, MB2, DB canals were taken to sizes K3 #35/.04 and the Palatal canal was enlarged to a K3 #45/.04 rotary file.

Obturation of the Root Canals
Analytic Autofit Greater Taper Gutta Percha™ (SybronEndo) in tapers .04 and .06 were used for obturation of the root canals. The gutta-percha cones were fit for point tug-back in each canal in the presence of NaOCl and a cone-fit radiograph was taken to verify correct length and fit. Final irrigation of the canals consisted of EDTA liquid, NaOCl, and then 95% ethanol. Analytic Autofit Greater Taper Paper Points™ (SybronEndo) were used to dry the root canals. A thick mix of Kerr Pulp Canal Sealer EWT™ (SDS Kerr) was prepared. A small amount of sealer was then placed on the tip of each master gutta-percha cone prior to being placed into the canal. A warm vertical method of obturation was used. The System B Heat Source™ (SybronEndo) was used for the down-pack according to manufacturer’s instructions. When the heat source was removed, the gutta-percha was then condensed using a Dovgan Plugger™ (Miltex Dental). The canals were then back-filled with gutta-percha using the Obtura II System™ (Obtura Spartan). The larger end of a Dovgan Plugger was then used to vertically condense the gutta-percha at each canal orifice. The coronal access was sealed with a temporary restorative material and post-operative radiographs were then taken (Fig. 5).

Fig. 5: Post-operative radiograph, tooth #15.

Conclusion
The design attributes of the K3 NiTi rotary file system allow for safe and effective root canal debridement. To date, the authors have not experienced breakage of any K3 NiTi rotary files; more than several hundred cases have been performed in a private practice setting. Furthermore, to maximize clinical safety and cutting efficiency, all rotary NiTi files may be considered to be single-use instruments. It is highly recommended that new techniques be tried on extracted teeth and/or in hands-on courses prior to clinical use.

This case report was adapted from an article by Frederic Barnett, DMD and Kenneth S. Serota, DDS, MMSc. Disclaimer: The authors have no financial interests in any of the manufacturers mentioned.

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Fred Barnett, DMD, received both his DMD degree (1978) and Certificate in Endodontics (1981) from The University of Pennsylvania, School of Dental Medicine. He was the former Director of Postdoctoral Endodontics at Penn and is a Diplomate of the American Board of Endodontics. Dr. Barnett has published over thirty scientific and clinical papers, served on the editorial board of Endodontics and Dental Traumatology and has lectured on all aspects of Endodontics nationally and internationally. He is currently an Associate Professor of Endodontics at Albert Einstein Medical Center in Philadelphia, and maintains a private practice limited to Endodontics.

Dr. Barnett can be reached at FredBarnett@hotmail.com or for additional endodontic discussion at www.dentaltown.com.

Kenneth S. Serota, DDS, MMSc graduated from the University of Toronto Faculty of Dentistry in 1973 and was awarded the George W. Switzer Memorial Key for excellence in Prosthodontics. He received his Certificate in Endodontics and Master of Medical Sciences Degree in nuclear medicine from the Harvard-Forsyth Dental Center in Boston, MA. In 1981 he was the recipient of the American Association of Endodontics Memorial Research Award for his work in nuclear medicine screening procedures related to dental pathology. Dr. Serota can be contacted at kendo@endosolns.com.

For product information on the K3 Rotaryfile system visit www.SybronEndo.com.