Written by Ricahrd Mounce, DDS Tuesday, 31 December 2002 19:00
(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.
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
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