December 1, 2006
by Rich Mounce, DDS
Having used all the rotary nickel titanium (RNT) systems available in North America, I have come to rely upon the K3 RNT system (SybronEndo, Orange, CA) as my preferred file. K3 stands in distinction to the other RNT root canal shaping instruments due to its asymmetrical design. The asymmetry of K3 makes the clinician power the file apically. Conversely, most other systems have a significant degree of symmetry in their design which makes them behave more like a wood screw, in that they will try to grab or become more engaged in dentin than otherwise would be the case if they were asymmetrical.
Many systems may excel in one category or another (cut well, resist breakage, etc.) but in my empirical opinion; no system surpasses K3s safety and efficacy across all categories. K3 stands out because it is flexible, cuts well, has excellent tactile control, resists breakage and is applicable to virtually any canal anatomy. The same cannot be said of all the various brands available at this time. In addition, K3 can also create larger master apical diameters (MADs) that are consistent with cleaner canals post instrumentation. This article will introduce the K3 in a clinically relevant manner.
K3 comes in the form of canal shaping files and orifice openers known as Shapers. The canal shaping files come in three tapers, .02, .04, .06, and a variety of tip sizes ranging from 15-60. The Shapers are available in three tapers .08, .10 and 12 and a fixed 25-tip size. The file is available in lengths ranging from 17-30mm depending on tip size and taper (Fig. 1).
1. Three radial lands. The third radial land is placed on the file to minimize engagement of the lands, stabilize the instrument and keep it centered in the canal (Fig. 2).
2. The radial lands are relieved to reduce the torque force loaded onto the instrument.
3. Added metal behind the cutting edge to provide maximum cutting efficiency and reduced dulling of the cutting edges.
4. A variable helical angle (Fig. 3).
5. A variable pitch.
6. Unequal flute widths.
7. Unequal flute depths. Both this quality and #6 allow for better channeling of debris out of the canal because the larger flute widths and depths can hold more debris that is not subsequently pushed apically.
8. A safe ended cutting tip (Fig. 4).
9. A constant core width of metal from the tip of the file to the handpiece.
10. A positive rake (cutting) angle (Fig. 5).
Sequencing of K3 use is most generally done from larger tapers to smaller and from larger tip sizes to smaller. Packaging of K3 instruments accommodates this sequencing of instrumentation. The files are available in various configurations that can be used as a self-contained pack for instrumentation of the vast majority of canals encountered. These pack configurations, the G pack, the Procedure pack and VTVT pack all represent variations on the same theme which accentuates the safety and efficiency of the file used from bigger to smaller tapers and tip sizes.
THE G PACK INCLUDES:
17mm 12/25, .10/25, .08/25, .06/25, .04/25, .02/25 K3’s in 21 and 25mm lengths. The Procedure pack includes: 17mm .10 .08 25 tip sizes and 40-25 tip sizes in both .06 and .04 tapers and 21 and 25 mm lengths. The VTVT pack includes: .10/25, .08/25, .06/35, .04/30, .06/25, .04/20 in 21 and 25mm lengths (all of the files in the sequence).
Other RNT systems are marketed for their ability to instrument root canal systems using a limited number of files (3-6 files). While the same benefits apply to K3 (entire canals can be prepared with only one G, Procedure and VTVT pack) , the K3 system also has greater application and flexibility in that not only can the canal be enlarged to the desired MAD. K3 does not impose an arbitrary limitation in canal preparation based on a reduced number of files. Beyond the G, Procedure and VTVT pack, K3 has a variety of files should another taper and tip size be desired at any stage. K3 is not a “one size fits” all system. It is unrealistic to expect that any given pack configuration can work with virtually every canal anatomy encountered.
As a matter of practical application, in clinical use, any one of the pack configurations can address virtually any canal and if truly exceptional anatomy is encountered, it is possible to either modify the sequence of files used by adding or subtracting files. While the G, Procedure and VTVT packs have only six files, it is often the case that not all of these files will needed in any given clinical case. The decision to use a G, Procedure, or VTVT pack is a matter of personal preference on the part of the clinician. None of the pack configurations is inherently better or more useful than any other; they simply represent options to the clinician with regard to dealing with the type of teeth commonly encountered, a choice not given by many other systems.
The manner of RNT use is key to the successful function of any instrumentation system, K3 is no different. Key strategies can reduce breakage and iatrogenic events of all types and produce ideal canal shapes prior to final irrigation and obturation. The strategies include:
1. A slow, gentle and passive touch in using the K3.
2. The file should be rotating upon entry.
3. The flutes of the file should be wiped after every insertion.
4. A goal to shape the coronal third first, the middle third second and the apical third last. Such a sequence is known as “Crown Down” instrumentation. Crown Down is consistent with early debris removal, enhanced volumes of irrigation, greater tactile control especially the apical third, less iatrogenic outcomes and more efficient canal preparation.
5. Copious irrigation at all stages in the instrumentation process. Such irrigation could be performed with 5.25% sodium hypochlorite, 2% chlorhexidine (Vista Dental, Racine, WI), Sterilox, or a combination of these solutions.
6. A viscous EDTA gel such as File-Eze (Ultradent, South Jordan, UT) should be placed in the canal especially in vital clinical cases and those necrotic cases where significant pulpal debris is encountered.
7. Hand file negotiation of the canal prior to the introduction of RNT is ideal, unless the canal is clearly open, patent and negotiable to its terminus at the minor constriction of the apical foramen. Such hand file negotiation should occur with small hand K files such as 6-10’s. These files should be precurved, especially in their apical 3-4mm and this curvature can be made three ways, with cotton pliers, by hand, or with an instrument like the EndoBender (SybronEndo, Orange, CA).
8. The creation of a glide path before RNT files are entered into the canal. A glide path exists when the given canal space has been opened at least to the equivalent of a size 15 hand file. Many narrow, curved and calcified canals will require a #6 hand K file to traverse them and begin the negotiation of the canal to some minimal diameter that then will allow a #8 to be entered into the space followed by a #10 and ultimately a #15 that can spin freely in the canal space. Then and only then is the canal ready to accept a RNT file sequenced as detailed in this chapter.
These strategies can maximize the safety and efficiency of all the RNT systems and their observance with K3 is also highly recommended.
In clinical technique, commonly, some variation of the technical sequence that follows will be used. It will be assumed that the roots are neither extremely curved nor calcified and a general dentist doing endodontics in daily practice would treat the tooth described:
1. Prior to initiating treatment, it has value to determine an estimated working length (EWL) of the tooth to use as a comparison to the final true working length (TWL) to be determined. The EWL will be used as a comparison to the value given by an electronic apex locator and bleeding point later in the final determination of TWL.
2. The pulp chamber
will be unroofed entirely in access ideally with the visualization of a surgical operating microscope (SOM) such as the Global SOM (Global Surgical, St. Louis, MO). After unroofing the pulp chamber, the application of File-Eze is recommended, especially if the pulp is vital or the chamber is filled with necrotic tissue. After removal of tissue in the chamber, File-Eze should be reapplied, and a #6 hand K file should be placed into the coronal half of the root to determine if the canal is patent or calcified. If the canal is open, patent, and easily accessed, the .12 Shaper can be placed into the canal gently and passively as described above. The canal can be irrigated, File Eze reapplied, and the .10 Shaper inserted gently to resistance and the canal irrigated and File Eze reapplied. Finally, the .08 shaper can be inserted. Usually, this sequence, in the clinical case described, will allow the insertion of .08 K3 Shapers to reach the middle of the root or the beginning of its most curved portion.
3. After copious irrigation, small hand files (6-10s) can determine if the canal is patent and negotiable to the EWL determined at the initiation of treatment. Aside from determining patency, the clinician can learn from this hand file exploration much about the three dimensional curvature of the root, degree of calcification, possible blockages, etc. It may take multiple insertions and new hand files to traverse the canal to the EWL especially if there is an acute curvature in the apical 2-3mm. Once the clinician reaches the EWL, it has value to use an electronic apex locator (EAL) to confirm the TWL. The EWL and the TWL should be very close in value, usually no more than .5-1.5mm different in value.
4. Prior to entering RNT files, the canal is taken to at least a 15-hand file to the true working length, irrigating as often as needed.
5. Once TWL is determined, the RNT can be used from larger to smaller tapers and tip sizes to smaller to being the final sequence of instrumentation in the middle and apical third. The Sequences for use would vary depending on whether the clinician was using the G, Procedure or VTVT pack.
For the G pack, the sequence is*:
For the Procedure pack, the sequence is (assuming .06 tapered files are used)*:
For the VTVT pack, the sequence is*:
*Each of these insertions requires that the recommendation for tactile use of the files be followed (gentle, slow, passive insertion minimizing engagement, 1-2mm of dentin ideally engaged with each insertion) and that irrigation ideally follow each insertion followed by recapitulation.
6. All of these sequences are used with the assumption that the clinician will repeat them as many times as needed in order to allow the desired file to reach the apical level of the canal as required by the clinical case. Most often in clinical practice, it will take 2-3 repetitions of the given file sequence after the Shapers are used to allow the files to reach the TWL. The TWL is most often verified again at this stage in the instrumentation. This verification occurs, aside from radiographic methods, with an EAL and possibly a bleeding point determination. The bleeding point is the point that can be marked reproducibly by a spot of moisture or hemorrhage on a paper point at the level of the minor constricture.
7. After the clinician can get a minimum of a .06-tapered 25 file to the minor constriction, the canal can be gauged. Gauging a canal means to determine the diameter of the minor constriction of the apical foramen. Gauging is best described by example. If a 25 K file binds at the minor constriction and resists displacement through the constricture, that is the diameter of the apical foramen and gives the clinician strong clues to the ideal size to which the canal should be enlarged.
8. While not commonplace, it is becoming more popular to enlarge canals to an MAD, which reflects the initial size of the minor constricture. With K3, it is possible to instrument the apical third to a 45 in an .02 taper and a 60 in an .04 and .06 taper. The creation of such larger MADs is consistent with cleaner canals in the endodontic literature. The sequence to create such a larger MAD may differ, dependent on the acuteness of the apical curvature. Generally, if the clinician has taken the canal to a .06 25, it is possible to use a sequence of .02 30, 35, 40, 45 followed by a .04 40 and 45, and so on both to the TWL and desired MAD making sure to recapitulate and irrigate after file. There are no universally agreed upon ideal MADs but the largest MAD possible given the curvature of the canal should be attempted taking into account all of the given considerations for tactile use of the K3. For many canals, the MAD will be a 50.
9. After the creation of an ideal master apical diameter, the clinician would then achieve cone fit and obturate the canal. While beyond the scope of this article it is noteworthy that the author bonds all obturation with RealSeal delivered via the Elements Obturation Unit and the SystemB technique (SybronEndo, Orange, CA). Preparation in the manner described with K3 can go far toward the creation of excellent shapes and facilitates cone fit and three-dimensional obturation of canal spaces (Figs. 6-7).
K3 compares favorably in the endodontic literature. Reading the literature about any product is often challenging because manufacturer’s recommendations may not have been followed, the statistical analysis of the findings may be unknowingly biased, sample size may not be adequate, amongst many potential problems. With these limitations in mind, a sampling of the literature on K3 shows that:
1. “K3s were significantly more resistant to cyclic fatigue than ProFiles” (Denstply Tulsa Dental, Tulsa, OK).1
2. “…nickel-titanium file systems including less tapered, more flexible instruments, like K3 and RaCe should be used in the apical preparation of canals with a complicated curvature.”2
3. “In the apical third, K3 rotary instruments were more efficient in removing gutta-percha filling material than the other techniques…”.3
4. addressing fracture resistance, when compared with Pro Taper “The percentage of broken files was…6.0% for the ProTaper group, and 2.1% for the K3 Endo group.”.4
5.”A significant difference was found between RaCe and K3 in terms of deformation and fracture of size 25, 0.04 taper instruments; K3 instruments had more favorable results.”5
6. “K3 rotary system was faster than Liberator to remove both gutta-percha and Resilon (p <0.05). Resilon/Epiphany was effectively removed with K3 or Liberator rotary files.”6
7. “…compared to ProFile, compression of the remaining smear layer is minimized when using the K3 rotary nickel-titanium system.”7
It is noteworthy that the only studies that are negative about K3 have the same author in common. A search of the “pubmed” website for “K3 Rotary Nickel Titanium” can give a comprehensive listing of the available studies for K3, and of course, other brands.
A comprehensive description of the K3 RNT system has been presented. The file system, in the empirical opinion of the author has the greatest blend of flexibility, fracture resistance, cutting ability and tactile control of the files available on the market. The author welcomes your questions and feedback.
1.Cyclic fatigue of three types of rotary nickel-titanium files in a dynamic model. J Endod. 2006 Jan;32(1):55-7. Yao JH, Schwartz SA, Beeson TJ.
2.The shaping effects of three nickel-titanium rotary instruments in simulated S-shape canals. J Endod. 2005 May;31(5):373-5. Yoshimine Y, Ono M, Akamine A.
3.Effectiveness of different techniques for removing gutta-percha during retreatment. Int Endod J. 2005 Jan;38(1):2-7. Masiero AV, Barletta FB.
4.K3 Endo, ProTaper, and ProFile sy
stems: breakage and distortion in severely curved roots of molars. J Endod. 2004 Apr;30(4):234-7. Ankrum MT, Hartwell GR, Truitt JE.
5.Deformation and fracture of RaCe and K3 endodontic instruments according to the number of uses. Int Endod J. 2006 Aug;39(8):616-25. Troian CH, So MV, Figueiredo JA, Oliveira EP.
6.Comparison between gutta-percha and Resilon removal using two different techniques in endodontic retreatment. J Endod. 2006 Apr;32(4):362-4. de Oliveira DP, Barbizam JV, Trope M, Teixeira FB.
7.Smear layer production of K3 and ProFile Ni-Ti rotary instruments in curved root canals: a comparative SEM study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006 Apr;101(4):536-41. Kum KY, Kazemi RB, Cha BY, Zhu Q.
Dr. Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Washington, USA. Amongst other appointments, he is the endodontic consultant for the Belau National Hospital Dental Clinic in the Republic of Palau. Korror, Palau (Micronesia). He can be contacted at Lineker@aol.com.
Dr Mounce has no commercial interest in the K3 system or any other dental product.