It's a Big Issue About a Little Tissue

A famous endodontist once said that , "It's a big issue about a little tissue." Removing this "little tissue" well through proper cleansing and shaping techniques has bedeviled generations of practitioners. There are probably as many endodontic instrumentation techniques as there are general dentists who do root canal therapy. The advent of rotary nickel-titanium files (RNT) in the past decade has helped revolutionize modern endodontic practice. A side effect of this advance has been a proliferation of different, often conflicting, methods of instrumentation and materials by different manufacturers. 

In order to present a real world and wet-gloved view of this issue, I would like to offer what has become my most common method of cleansing and shaping root canal systems for an average case. This technique is essentially independent of the file type used, although I recommend the K3 RNT marketed by SybronEndo because of the files' fracture resistance, variable tip sizes, and robust handling characteristics.

(1) Preoperatively, assess for length of tooth, strategic value of the tooth, estimated numbers of canals and roots, root curvature, calcification, periodontal status, restorability, access difficulties, etc, and take multiple angles (three) of preoperative radiographs.

(2) Access is always straight-line. Files never should deflect off access walls as they make their way into canals, especially RNT files.

(3) Canals are divided into thirds: coronal, middle, and apical. The coronal third is instrumented first, the middle third second, and the apical third last so as to give the greatest tactile sense to instruments working in the apical third, and also provide for the optimal exchange of irrigants.

(4) Initially, in a vital or necrotic tooth and in the presence of EDTA and sodium hypochlorite, I use a Quantec Flare Series 0.12 taper, size 25 tip, 21-mm (SybronEndo) orifice opener into the coronal third to gain a toehold. The additional smaller Quantec orifice openers can be used in the same fashion (still in the coronal third) slightly deeper to give better apical-third shape. Sodium hypochlorite is used to flush away debris and EDTA is re-applied.

Fig. 1. A recent case (No. 9) treated by the author in the manner described. Notice the difference in shape and patency between Nos. 9 and 10 (done elsewhere).

 

Figures 2 and 3. Two clinical cases treated in the manner described.

(5) For the middle third, I first scout with a No. 6 and a No. 8 K file to make sure that the canal is patent and determine if there are hidden canal curvatures. Once patency and canal curvature are determined, the 0.06 35 tip size K3 is used approximately to the junction of the middle and the apical third. If the 0.06 35 tip size K3 will not advance to this level, the 0.06 30 or 25 tip sizes can be used instead. Recapitulation and irrigation are frequent.

(6) The apical third requires a gentle touch. Extensive time per canal (as long as it takes) is required to explore the apical third with hand files starting with 6, 8, and 10 K files to reach an estimated working length. The files are entered passively in the canals and never forced to a preconceived or estimated length. Once a 10 or a 15 K file gets to the estimated working length, a radiograph should be exposed to determine the true working length (TWL), and this should be confirmed by tactile sense, a bleeding point, and electronic apex location. Maintaining canal patency and leaving the foramen at its initial position and at its initial size is critical.

(7) Once TWL is established, a glide path to the apex for subsequent RNT files should be established with hand files. This glide path should open the given canal to approximately a size 20 K file to TWL. At this stage TWL has been determined, the coronal and middle thirds prepared, and the canal instrumented to approximately a 20 K file at TWL.

(8) Regardless of the particular system used, RNT files are introduced in a crown down fashion (larger to smaller RNT files used coronal to apical) until TWL is reached. For example, the 0.06 K3 files could be used from a 35 tip size (or larger) down to a 20 or 15 tip size, and the sequence repeated. In smaller canals, the 0.04 K3 files could be used in a similar fashion.

(9) Prior to deciding to what size to shape the apex, it is essential to determine the diameter of the foramen or gauge the apex. Gauging is best described by example: If a 25 K file will slide to the TWL and gives a resistance to apical displacement through the foramen, then the No. 30 tip size K3 of an appropriate taper (if it will advance passively) will be used to TWL to create shape above the foramen to give an acceptable cone fit. Gauging the apex allows shape to be created above the foramen while maintaining its size and location.

(10) The final shape imparted to the canal by a given K3 file can be matched by both a paper point and gutta-percha point of the same taper (Autofit gutta-percha and paper points, SybronEndo). In other words, a 0.06 tapered K3 file used to TWL can be matched to a 0.06 Autofit gutta-percha and paper point. This facilitates predictable cone fit and/or subsequent obturation for noncarrier-based warm gutta-percha techniques. I would strongly recommend a cone-fit x-ray with the gutta-percha point in place prior to obturation to confirm working length and the final canal preparation shape. 

Several tips on the above sequence: (1) If an instrument doesn't want to go to place, don't force it. Use an instrument that is smaller or larger either to create more shape above the point of difficulty or bypass it, but never force the instrument to try to save time. Forcing the instrument increases the chance of instrument separation. (2) Frequent irrigation and recapitulation are essential. Use either EDTA or sodium hypochlorite at all times during instrumentation. EDTA is especially helpful in the early stages of a vital case. Creating and pumping a ball of pulverized pulp tissue into the narrowing cross-sectional diameters of the root canal system (by not recapitulating, irrigating enough, or using EDTA) can be very difficult to bypass or subsequently dissolve. How often should you irrigate and/or recapitulate? In some calcified, curved, and difficult roots, after every RNT file use. 

CONCLUSION 

With the advent of RNT files, cleansing, shaping, and obturating root canal systems and dealing with a "little tissue" has never been more predictable. The guidelines above, while not applicable for every tooth, can for the vast majority of cases encountered help diminish instrument fracture and provide a framework for faster, more enjoyable, and more profitable endodontics (Figures 1, 2, and 3).


Dr. Mounce is in private endodontic practice in Portland, Ore. He lectures worldwide and has written numerous articles for journals including Dentistry Today and the Journal of Endodontics. Dr. Mounce will be presenting multiple 1-day courses (lecture, hands-on and demonstration included) on cleansing, shaping, and obturation of the root canal system in Southern California in September 2003. For more information, Dr. Mounce can be reached at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

 

 



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