For a host of reasons, I am a strong advocate of the use of .02 tapered rotary nickel titanium files in endodontic instrumentation. While some endodontic teachers discount their use, in my hands, these files have significant application and value. Without them, I would feel at a genuine disadvantage. I think that those who might try to discredit the use of .02 tapered RNT files simply either have not given the files the chance they deserve, or they might be using a less efficient brand of file.
.02 tapered RNT files provide a significant bridge between hand and rotary instrumentation. This is especially true in regard to enhancing and refining the glide path that should be created in canals with small hand files before RNT files of all types are placed into a given third. First, as a rule, it is important to hand-negotiate and explore canals with hand files prior to creation of a glide path, especially in the apical third. Once a canal is enlarged to approximately a 10 to 15 K file, a .02 tapered file, such as the K3 by SybronEndo (Orange, Calif.), can be used in increasing tip sizes - from 15 to 20 - to more fully enlarge the canal. This creates an ideal preenlarged canal that can be instrumented fully in a crown-down manner. Such a crown-down manner would involve using rotary files from a larger taper and tip size to smaller ones.
In addition, once the true working length is determined, assuming it is determined early in the instrumentation sequence, .02 tapered K3 files can be used from a .02, 15-tip size and increase in tip size from apex to the point to where the larger files will no longer easily advance apically to the true working length. Such a movement removes restrictive dentin, most often at the junction of the middle and apical third of the canal. Said differently, use of .02 tapered rotary files from true working length - after glide path creation - by a .02, 15-tip size to the largest file that will easily advance creates “deep-body shape.” This term refers to the continuation of taper in the portion of the canal directly above the apical third. Creation of such deep-body shape is essential for ideal irrigation in the apical third and placement of larger, tapered instruments beyond what is often the most curved portion of the canal.
In my empirical experience, the .02 tapered K3s easily can be inserted - after glide path creation - from approximately a 15- to 30-tip size to true working length prior to the crown-down instrumentation that subsequently takes place.
In actual practice, the sequence progresses in the following manner:
1) Creation of straight-line access
2) Canal negotiation (i.e., a determination that the canal is open and can be traversed with small hand files to its most apical extent)
3) Achievement of patency
4) Coronal and possibly middle-third orifice shaping
5) Glide path creation to approximately a 15 K file to reach the true working length
6) A .02 tapered K3 file can be placed gently to the true working length to refine and enhance the glide path. Generally, this file will slide easily to length. Usually, it is then possible - and feasible - to take a 20-tip size, .02 taper to the same length followed by a 25- and often a 30-tip size or larger. If any of these files will not advance easily, they never should be forced. Using this sequence can go a long way toward creating an excellent shape at the junction of the middle and apical thirds. Even more importantly, you have created a smooth and reproducible track for subsequent rotary files that follow.
7)After this use of the .02 tapered files, final canal instrumentation can be achieved crown-down with larger tapers and tip sizes to smaller sizes in order to reach the true working length. This step is followed by a gauging of the canal and selection of a final master apical diameter.
In summary, I think that .02 tapered RNT files can give a clinician an excellent blend of flexibility, negotiation, and function. They also help to expedite the process of opening the junction of the middle and apical third. This improves the flow of irrigants into the apical third while maintaining the canal in its original position, and creates a more reproducible path for shaping files.
As always, I welcome your questions and feedback.
Dr. Richard Mounce is in private endodontic practice in Portland, Ore. Dr. Mounce is the author of a comprehensive DVD on cleansing, shaping, and packing the root canal system for the general practitioner. The material also is available as audio CDs and a Web cast pay-per-view. He lectures worldwide and is a widely published author. For more information, contact Dr. Mounce via e-mail at comfort@MounceEndo.com. Visit his Web site at www.MounceEndo.com.