23 File Systems
RaCe and S-Apex
Summary and Conclusions
The Alpha system, developed in 2005, consists of NiTi instruments with tapers of 2%, 4%, 6%, and 10%. The ISO sizes range from 20 to 50. The Alpha files are commercially available in two different cross-sectional conformations.
The files for coronal widening are kite-shaped in cross section with 10% taper. Their large chip space makes them a good choice as the first instrument to work with. This “pre-enlargement” provides improved tactile control and makes possible an improved insertion path with the prebent size 10 K file. This makes the introduction of other files into the canal less complicated by reducing the chances of coronal sticking of the files and permits a larger quantity of irrigating fluid to be used to improve the cleaning and antibacterial effect, thus reducing postoperative complications to a minimum.
For the apical finish, instruments with a pentagonal cross-section should be used. This design aims to prevent instrument fracture; the tested torque values are the highest in comparison to all other instruments. The negative cutting angle achieves passive dentin removal and prevents excessive cutting into the root canal wall.
All instruments are coated with a layer of titanium nitride. This process guarantees the maintenance of sharpness even following repeated sterilization (Schäfer, 2002). The speed of rotation of the orifice-widening files should not exceed 800 rpm; all other instruments are used at a speed of 250 rpm. The instrumentation is carried out using the crown-down technique with increasing taper of the instruments. Following coronal widening of the canal orifice, the initial depth is prepared with a file with 6% taper. The 4% file can be used up to 2 mm above the apex, and the 2% file is then used to the full working length.
Size selection is carried out with the apical “scouting” file: Using the size 8 file, the canal is instrumented using the yellow sequence, increasing the file size by one number at a time until the final apical opening corresponds to a size 25 file tip.
The FlexMaster system (VDW, Munich, 2000) is characterized by a large assortment of root canal instruments of various sizes (15–70) and tapers (2%, 4%, 6%). The instruments are fabricated from a 55-nitinol alloy. The convex instruments exhibit an increased resistance to torsion and therefore reduced danger of fracture within the canal.
FlexMaster instruments are used at a constant rotation speed of 150–300 rpm. The instrumentation of the root canal is carried out using the crown-down technique. As with all other nickel titanium (NiTi) systems, the FlexMaster files should only be used in a torque-controlled handpiece to avoid the danger of the file getting stuck in the canal and possibly fracturing because of torsion.
Depending on the size of the root canal, instrument manufacturers recommend a variety of file sequences for instrumentation as a guide for narrow, middle, and broad canals, which are represented by color coding in the instrument set. For example, the start of the sequence for a broad root canal involves the use of an Introfile following exposure of the root canal orifice for instrumentation of the coronal segment of the canal with a.06/30 instrument.
Following the principles of the crown-down technique, files of sizes.06/25,.06/20, and.04/30 are recommended. The apical preparation is subsequently carried out to the desired size using .02 taper files.
The cleaning efficiency of FlexMaster files is universally viewed as positive (Hülsmann, 2003). However, in comparison to purely hand instrumentation, canals instrumented with the FlexMaster files exhibit a larger smear layer as well as residual debris (Schäfer, 2002).
With regard to the shaping of the root canal and to the original root canal axis, the FlexMaster system is clearly superior to conventional, manual instrumentation (Schäfer, 2002). Even narrow and severally dilacerated canals can be almost perfectly instrumented and prepared for root canal filling (Hübscher, 2003).
The rotary NiTi K3 file system (K3 RNT; Sybron-Endo, Orange, CA, USA) differs from other available systems because of its asymmetric design, which gives it extraordinary flexibility, cutting efficiency, tactile control, and fracture resistance. The K3 file system should be used clinically based on the following prerequisites:
• K3 files must be passively and gently inserted;
• each time the file is inserted only 1–2 mm of dentin should be removed;
• irrigation and recapitulation should follow each K3 file insertion.
After traversing the full length of the canal and manual widening with a K file of at least size 15, the K3 file system is used with the crown-down technique.
The variety of file types in the K3 file system is large: for coronal enlargement, files with a taper of.08,.10, and.12 and a tip diameter of size 25 are available. For canal shaping, files of taper .02 and sizes 15–45 as well as tapers of.04 and.06 in sizes 15–60 are available. Corresponding gutta-percha points of taper.04 and .06 in sizes 15–45 complete the K3 set-up.
The manufacturer recommends three file sequences:
• The Procedure Pack:.10/25 and.08/25 should be used for enlarging the access cavity, and sizes 40–25 (taper.04/.06) for the crown-down preparation.
• With the G-Pack, the tip diameter remains constant at size 25, and the taper varies from.12 to.02.
• With the VTVT Pack there is a change in taper (variable taper) and tip diameter (variable tip), which is generally regarded today as an adequate and fracture-reducing clinical model.
K3 has to date been reported in 33 publications. K3 files are much more resistant to cyclic fatigue than ProFile (Yao et al., 2006) in the 40/.04 and 40/.06 sizes, and also more resistant to fracture (Ankrum et al., 2004 [although not statistically significant], Troian et al., 2006). On the basis of its effectiveness in removal of gutta-percha, the K3 file system has been recommended for endodontic retreatment (Masiero et al., 2005; de Oliveira et al., 2006):
K3 files also help to precisely prepare the apical anatomy in complex root curvatures and minimize compression of the smear layer (Yoshimine et al., 2005; Kum et al., 2006).
LightSpeed instruments are made of NiTi indicated for root canal instrumentation. They were developed by Wiley and Senia and entered the commercial dental market in 1993. A classic Light-Speed set consists of 22 instruments of ISO sizes 20–100. Between sizes 20 and 70, half-sizes are also provided (22.5, 27.5–65). The root canal is instrumented at a speed of 2000 rpm.
In contrast to the conventional endodontic instruments, which have a 16-mm long working section, LightSpeed files have a long, thin shaft and a short working end with a blunt tip.
The length of the working section depends on the ISO size. For example, the size 20 file has a 0.25-mm long cutting section whereas the size 100 file has a cutting section that is 1.75 mm long.
During root canal preparation, the noncutting tip points away from the canal wall and the file is thus retained in a more central position. Because of the high flexibility of the instrument shaft, the danger of “straightening” the canal is significantly reduced (Glosson et al., 1995; Shadid et al., 1998; Hülsmann et al., 2003).
The major advantage of the LightSpeed system is gentle coronal instrumentation and minimal removal of hard tissue. Both of these are critical factors for posttreatment ability of the tooth to resist fracture (Lang et al., 2006). A disadvantage is the very large number of instruments required.
Since mid-2006 the LightSpeed eXtra (LSX) system has been available on the commercial market; it will eventually replace the LS system. LSX consists of only 12 instruments of sizes 20–80. The new instruments are not manufactured using the grinding process because this mechanical process can lead to imperfections of the surface (Eggert et al., 1999), which can later lead to instrument fracture.
LSX files are punched out of raw stock. The head of the instrument has a short and flat working area with two radial lands and a blunt tip. The long, thin instrument shaft of the LightSpeed files is unchanged in the LSX system. The recommendation is to utilize these instruments at 2500–3000 rpm and a higher level of torque. These modifications of the LightSpeed system have been designed to simplify the technique and reduce the risk of instrument fracture. The advantages of LS with regard to canal straightening and loss of working length remain unchanged (Iqbal et al., 2007).