The goal of root canal therapy is the three-dimensional cleansing, shaping and obturation of the root canal space from the canal orifice to the minor constriction of the apical foramen.
Endodontic therapy can succeed because, to the greatest extent possible, the pulp is removed from the root, duplicating the net effect of pulp extraction. Extraction heals the patient because the entire diseased pulp is removed. The degree to which we can duplicate the effect of extraction in endodontic treatment (after the placement of a post-endodontic coronal seal) determines healing and clinical success. Mechanisms to clean the root canal space have varied considerably over the past decades in concept, philosophy and equipment means.
The cleansing aspect of endodontic therapy is a blend of mechanical shaping of the root canal system with antimicrobial irrigation to reduce bacterial counts and pulp tissue within the root canal system. This antimicrobial effect is achieved with a combination of irrigation (chlorhexidine and sodium hypochlorite most commonly) as well as inter appointment intra canal medicaments, usually calcium hydroxide. The extent to which canals can be shaped ideally and done so without iatrogenic outcomes improves clinical success. Viewed in this light, it has great value to depend on a rotary nickel titanium (RNT) instrumentation system that cuts effectively, does not lead to transportation of the canal, does not fracture and has an excellent tactile sense.
One method, which has stood out amongst its competitors in the marketplace in the past decade, is the K3 RNT file system (SybronEndo, Orange, CA, USA). It is the empirical opinion of the author that this file, in combination with correct use and copious irrigation, has the greatest flexibility, fracture resistance, cutting efficiency and tactile control of any RNT file on the market at present.
The K3 system is a complete system, i.e. there is not any one single canal anatomy that would require or argue for application of another system (an attribute which is not
possessed by many of the other systems available). The files are applicable in any canal anatomy if used in the correct sequence and with the right touch, tapers and tip sizes. The system is sufficiently flexible to handle any curvature – the same cannot also be said of all other available RNT systems.
Within the available packaging configurations of K3, one configuration stands out for its application, the G pack. This configuration comes in a 25mm 21mm variety. Each pack contains one file each at .12, .10, .08, .06, .04, and .02 tapers, each with a #25 tip size. The G pack is one of several packaging configurations of K3 files. It represents one manner in which K3 files are used by a significant number of K3 users. It is not inherently better than the other packaging configurations, but the G pack represents one common method of usage. Personal preference determines which K3 configuration is employed.
The configuration has a number of advantages. For the experienced clinician these can shape a root canal to create a ‘basic’ preparation, one upon which the clinician can create larger apical diameters if needed or desired. The G pack stands in contrast to the Procedure Pack and the VTVT K3 pack (SybronEndo.com).
The K3 G pack has clinical value because it can be used across the broadest range of clinical cases. The G pack alone, without other K3 files, is not meant to handle every tooth that might be encountered, but it can be used to provide the clinician ideal cleaning and shaping possibilities for the vast majority of cases that will be encountered, especially if it is used appropriately in the manner described within this article. The K3 G pack has value amongst many reasons, one of which is its diminishing taper meaning that each subsequently inserted K3 file is a smaller taper that is inserted further apically. This sequence allows the clinician to place the next K3 into the canal with greater tactile control than the last and into a canal with greater irrigation in place. Each subsequent file will work against less resistance because it will be touching less surface area of the canal wall i.e. minimal engagement relative to a file, which is being used to cut along its entire length.
Instrumentation of root canals is a dynamic process. In other words, the clinician is advised against trying to instrument all canals to a given and arbitrary apical diameter every time. Such rigid thinking and clinical practice is the precursor to separated files, ledging, perforation and transportation and other such iatrogenic events. The K3 G pack provides one method that, if used with the right touch and in the correct sequence, can instrument root canal spaces safely and efficiently.
The use of the K3 G pack should be performed with the following clinical, manual and ‘tactile’ considerations:
1. The files should be turning on insertion into the canal.
2. The canal must have lubrication in it during all stages of instrumentation to reduce torque and friction on the file.
3. Insertion should be gentle, passive and never forced.
4. Engagement of the file on the canal walls should be minimal, ideally 1-2 mm per insertion. The greater the engagement of the file on the canal walls, the greater the chances for torque related failure for any rotary nickel titanium system.
5. A hand-created glide path must precede use of the RNT file, ideally a #15 hand created glide path so as to minimise RNT fracture.
6. Ideally, the canal will be instrumented Crown Down (CD) meaning that the coronal third of the canal will be instrumented first, the middle third second and the apical third last. In other words, the clinician will not attempt to instrument the middle or apical third until the more coronal thirds of the canal have been fully addressed.
7. Irrigation is frequent, copious and the irrigant is left long enough in the canal to maximise its biologic effectiveness. For the author, that will require the use of approximately 90-150 cc of 2% chlorhexidine and sodium hypochlorite (5.25%) delivered via a close ended side venting needle from pre-measured and disposable plastic irrigating syringes in an average molar. As an aside, these two irrigants above are never mixed as doing so can cause a brown precipitate which can be difficult to remove from the canals. As an intermediate flush between the two irrigants above, as well as to clear the smear layer for bonded obturation, the author will use SmearClear (SybronEndo, Orange, CA, USA).
8. As a K3 file is inserted into the canal, it should not be pumped up and down. Once the file reaches its maximal insertion, the clinician should use the next file in the sequence, not keep taking the previous file to the same location.
9. Instrumentation sequence, irrespective of the particular K3 in use, will be similar: the clinician will assure that the canal is patent and that a glide path has been created. Then and only then will RNT files be used. The clinician will subsequently recapitulate, irrigate and then repeat the sequence as needed. In other words, the canal will be always be explored first by hand to assure patency, a glide path will be created, then K3 files will be entered as detailed elsewhere with regard to sequence and touch. The canal is then irrigated, recapitulated (K files are entered into the root to assure that the canal is still patent) and the sequence repeated as many times as needed to instrument the canal. In some canals, assurance of patency and glide path creation is a formality, in others, locating, negotiating and creating a glide path can take significant time and effort. What is important is that the clinician remembers to follow these sequences so as to properly shape the canal and prevent iatrogenic outcomes.
10. In general, RNT files ideally are used from larger tapers to smaller and from larger tip sizes to smaller, such a sequence is inherently CD. CD instrumentation has many benefits including increased irrigation volumes earlier in the sequence, improved debris removal, improved tactile sense, fewer iatrogenic events of all types and less debris pushed apically.
Specifically, the K3 G pack is used in the following manner clinically:
1. Straight line access is obtained. Ideally, such access is obtained using enhanced visualisation and magnification, such as that provided by the surgical operating microscope or at a minimum loupes with an additional light source. Ideal access implies that all the canals can be visualised in one mirror view and that special attention has been given to location of all canals which may not commonly be found such as the MB2 canal in upper molars, the second canal in lower anterior teeth and second distal canals in lower molars which might branch off below the pulpal floor. The cervical dentinal triangle must be removed where present so as to prevent unnecessary torque forces from being applied to the files.
2. After location of the canal, the canal is explored in thirds (beginning in the coronal third) with small patency files, usually from 6-10, as needed, in small, very curved and calcified canals.
3. To utilise the K3 G pack to its greatest efficiency, begin CD instrumentation by taking the .12 Taper K3 Shaper to resistance, never attempt to take it or any orifice opener beyond the point of greatest curvature in the root. Irrigate and recapitulate. This Shaper must be inserted passively so that it is not forced and if the canal resists its advancement, it is withdrawn and the next instrument in the CD sequence inserted. The canal is then irrigated and recapitulated.
4. Next, the .10 Taper K3 Shaper is taken to resistance. The canal is then irrigated and recapitulated. It should advance slightly more apically than the first Shaper. After use of these two Shaper files, in the vase majority of clinical cases, the majority of the pulp has been removed from the canal and as such usually working length can be determined at this time as described below.
5. If the clinician desires to establish working length, it is possible usually to do so now with an apex locator such as the Elements Diagnostic Unit (SybronEndo, Orange, CA, USA) or alternatively, a radiograph may be taken, or both.
6. Next, take the .08 taper K3 Shaper to resistance, again, no further than the point of greatest canal curvature. The canal is then irrigated and recapitulated.
7. Take the .06 Taper #25 K3 File to resistance. The canal is then irrigated and recapitulated. Many relatively straight and mildly curved canals will be instrumented very close to the true working length at this point and if the clinician wishes to finish the preparation at an apical diameter of 25, these four files can often achieve the desired result. The clinician would then fit a cone and obturate the canal, ideally with a warm obturation method.
It is noteworthy that many clinicians around the world are beginning to realise the value in creating larger master apical diameters for root canal instrumentation. The endodontic literature is very clear that larger master apical diameters create cleaner canals relative to smaller master apical diameters. Simply put, instrumenting canals to a 50 or 60 at the TWL will allow greater volumes of irrigation to move apically with significant antibacterial effect. In addition, the mechanical removal of dentin in the apical third also removes pulpal tissue that otherwise would remain with a final smaller prepared master apical diameter. The K3 system is complete in that it is possible to instrument canals to a size 45 in the .02 taper, and 60 in the .04 and .06 taper although the creation of larger apical diameters with K3 would require purchasing more files than simply a G pack.
8. In more difficult, curved and narrow canals, the clinician can use a .04 Taper #25 K3 File and a .02 Taper #25 K3 File until working length is achieved. It is important that the clinician understands that they will likely have to make multiple insertions and entries of the files in the canal to reach the desired canal length. The sequence of hand file exploration, patency and glide path creation, rotary file use as described, irrigation and recapitulation, will have to carried out multiple times in most canals to reach the desired length.
9. The manufacturer recommends 350 RPM for rotational speed. While this speed might be ideal for a clinician new to K3 use, it is possible to safely and efficiently employ higher speeds. After gaining experience, it is possible to use speeds up to 900 RPM for K3 RNT use, but such a rotational speed is a matter of practice and proficiency, not due to a limitation in the K3 system. Increased speeds should be worked up to with experience and are not advisable for the novice clinician.