In clinical practice, cyclic fatigue will increase in curved canals (the smaller the curvature radius or double curvature the higher the risk) and torsional fatigue in small and obliterated canals (tip lock; Figs. 1–3). The type of NiTi files (design, taper, size) and the instrumentation technique (crown-down or step-back, brushing or pecking motions) may overcome these anatomic challenges and prevent file separation. Another major clinical technique for reducing the risk of NiTi file separation is to perform coronal enlargement and manual pre-flaring to create a glide path before using NiTi rotary instruments (Fig. 4).[9–11] It has been shown in the literature that establishing a glide path by coronal pre-flaring and manual canal scouting is a fundamental clinical step for safer use of NiTi rotary files. Berutti et al.[12] have shown that creating a manual glide path with a #20.02 manual stainless steel (SS) file decreases the frequency of NiTi rotary file separation by six times. However, creating a glide path and coronal pre-flare with small SS files (#06–08) in curved, constricted or obliterated canals will result in several clinical complications, such as file deformation, buckling, separation and the need to use several instruments (Fig. 5). This is because SS small-diameter files are highly flexible, often leading to torsional fatigue and flute deformation. In addition, straightening of the original canal can occur with the use of even these small files in severely or double-curved canals.

 

Recently, FKG Dentaire introduced its Scout-RaCe and RaCe ISO 10 files, NiTi rotary file systems for mechanical pre-flaring and creating a glide path to replace SS hand filing at this phase of canal preparation. It has been demonstrated that the use of these NiTi instruments prior to the main NiTi rotary files better retains the original canal anatomy, with less modification of canal curvature and fewer canal deviations compared with manual pre-flaring performed with SS K-files.[8,12] In addition, challenging canals that would take a considerable amount of time to initiate with SS files can be completed quickly with this new technology.

In this case report, we will present the indications and protocols for the use of Scout-RaCe and RaCe ISO 10 files (Fig. 6).

Scout-RaCe files

This system consists of three NiTi files with a RaCe flute design (alternating cutting edges), which is considered to be a non threading design owing to its alternating pitch from parallel to spiralled zones.[14–17] The surface of these files is electropolished in order to remove all irregularities produced during grinding. The tips are non-cutting and rounded. They are produced in lengths of 21and25 mm with a 0.02 taper. They have a triangular cross-section and come in sizes #10 (purple), 15 (white) and 20 (yellow). These files have two silicon stoppers, one called SMD (safe memory disc), which lies close to the handle and is yellow, indicating the taper of the files (0.02), and a smaller stopper that indicates the length of the files (red=21 mm and blue=25 mm). These files are used in severe single or double-curved canals and they will primarily scout the canals with minimal coronal flare (Fig. 7).

Clinical protocol for Scout-RaCe files (severe single and double curvatures):

1. If possible, use a #06 or 08 K-file file to reach the estimated working length (WL). Confirm the length with an electronic apex locator (EAL).
2. Irrigate with NaOCl.
3. With gentle strokes at 600 rpm, widen the canals with the #10, 15 and 20 Scout-RaCe instruments to full length. Since these files are very flexible, avoid excessive pressure to prevent buckling. Irrigate the canals with NaOCl between files and clean the files if used for more than four strokes. Use a #15 K-file to obtain a smooth glide path and confirm the WL with an EAL.
4. Continue with the main NiTi sequence (BioRaCe, Sequence files, etc.; Figs. 8 & 9).

RaCe ISO 10

This system consists of three NiTi files with the same RaCe flute design as described above. They are produced in lengths of 21 and 25 mm. The difference between Scout-RaCe and RaCe ISO 10 is that these files progressively increase in taper but maintain the same apical diameter of 0.10 mm. These three files come in size #10 and tapers of 0.02, 0.04 and 0.06 (Fig. 6). The SMD silicon stopper is yellow for the 0.02 taper files, black for the 0.04 taper and blue for the 0.06 taper. The colour of the small silicon stopper indicates length as with the Scout-RaCe files. These files are meant to be used in constricted and obliterated canals, as well as in abrupt coronal curvatures. These files, like the Scout-RaCe files, will also scout the canals but because of the progressive increase in taper will primarily perform coronal flaring (Fig. 10). The #10.04 and 10.06 RaCe ISO 10 files are more rigid than the #15 and 20 Scout-RaCe files, and that is why they are for use with vertical pressure for constricted or obliterated and curved canals (will not buckle as easily as Scout-RaCe files) and are not ideal for double and severe curvatures.

Clinical protocol for RaCe ISO 10 files (constricted or obliterated canals):

1. Use a #06 or 08 K-file to reach the estimated WL. Confirm the length with an EAL. Remove the file and verify that the curvature is not severe by inspecting the file’s surface.
2. Irrigate with NaOCl.
3. With gentle strokes at 900 to 1,000 rpm, widen the canal to WL with the #10.02 and 10.04 instruments. If necessary, continue with the #10.06 file at 600 rpm.
4. Irrigate the canals with NaOCl between files and clean the files if used for more than four strokes. Use the #15 K-file to obtain a smooth glide path and confirm the WL with an EAL.
5. Continue with the main NiTi sequence (BioRaCe, Sequence files, etc.; Fig. 9).

Conclusion

Scout-RaCe and RaCe ISO 10 NiTi rotary files offer the following advantages over SS files for attaining initial flaring and glide path:

_improved speed and efficiency;
_less initial canal transportation in both experienced and non-experienced hands;
_predictable patency;
_limits the need for the initial use of multiple SS files in constricted and severely curved canals;
_makes severely and double-curved canals predictable for the traditional NiTi instruments that follow.

Editorial note: A complete list of references is available from the publisher.