SHAPING ROOT CANALS (continued)

I highly recommend the Digital Torque Control (DTC) motor available through Dentsply Tulsa Dental. It has excellent torque control and pre-programmed settings for the NiTi rotary instruments on the market, including the ProTaper files.

All ProTaper instruments were designed to work at maximum torque (520 g.cm) and at 275-300 rpm. Further, there is published science confirming a high torque value for ProTaper. Elio Berutti published an article in the April 2004 issue of the JOE, pages 228-230. In this article, Berutti compared preflaring versus no preflaring and within these two categories, compared rotation to failure using high versus low torque values. In this Berutti paper, a very serious increase in instrument failure (approx. 3-5 times) was noted when ProTaper files were driven at dangerous low torque values. As such, I run ALL ProTaper instruments at the maximum torque on my electric torque control motor in order to work "optimally" and "safely".

Taper lock is the phenomenon where a file binds against dentin over the length of its cutting blades. ProTaper files are the only progressively tapered instruments on the market and their design prevents them from binding against dentin over length. Instruments that bind in the canal engage and tend to screw into the canal. This is exactly why we use ProTaper shaping files in a brushing action to laterally cut dentin in the coronal two-thirds of the canal. This specific method of use creates space so the instruments' larger tapers don't bind, grab or screw. In summary, it is the unique design of a file and the method of use that prevents taper lock, grabbing and the screw effect.

As I state in my lectures, I always use the sequence S1/S2 initially to pre-enlarge the coronal two-thirds of a canal, regardless if the canal is straightforward or difficult and regardless if I could go to length initially and confirm a smooth, reproducible glide path. I like to use the ProTaper Shaping files like brushes to remove gross amounts of tissue and/or restrictive dentin in the coronal two-thirds. My rotary apical one-third sequence, after establishing working length/patency and confirming the glide path, is S1/S2/F1, then gauge. Some clinicians like to go to length first with hand then rotary files even though, in more difficult cases, it is oftentimes more challenging. However, this technique can work.

Some colleagues start by taking the S1 followed by the S2 to length. If you try to go to length immediately with any rotary, there is a significant increase in binding and broken instruments. I sequence the root canal preparation into coronal two-thirds, then apical one-third. Since I am initially restricting the shaping files to the coronal two-thirds of the canal, then recognize the larger, more active cutting blades of the S1 and S2 files won’t fully prepare this region of the canal during this phase of shaping. If you did go to full working length immediately, then the S1 has been designed to perform about 80% of its work in the coronal one-third, 10% of its work in the middle one-third, and 10% of its work in the apical one-third. Following the use of the S1 file, the S2 will not further enlarge in the coronal one-third; rather it will perform about 80% of its work in the middle one-third and about 20% of its work in the apical one-third. The work of the S2 file in the apical one-third facilitates the safe use of the F1. In summary, the S1 and S2 files dominantly prepare the coronal two-thirds.

The three Shaping files are the only instruments in the series that may be used like a brush. Brushing action is used to enlarge canals more than the size of any given Shaping file or to selectively relocate a canal away from an external root concavity. Since a Shaping file is loose in the canal during the outward brushing stroke, you can definitely use the Shaping files in a brushing motion for longer than three (3) seconds.

All ProTaper files, when used sequentially, will efficiently cut dentin and easily move into a canal which has first been secured with hand files. If any given instrument will not move deeper into a canal, it means:

1. The canal is too small to accept the file -- As such, recapitulate with the 10 and 15, or even a 20, hand file to create sufficient space for the rotary files to follow.
2. The canal contains debris.
3. The file contains intrablade debris which deactivates the file.
4. The terminal extent of the file is too stiff to follow the anatomy of the canal.

The pecking motion has been advocated as a safety prevention for various NiTi rotary file lines that have a fixed taper so any given file won't grab and get inadvertently pulled into the canal. Because of the multiple tapered design on each shaping file and a more efficient cutting blade design, ProTaper files are never used with a pecking motion and require no inward pressure to safely and effectively cut dentin.