In the beginning we had K-Files, Reamers and Hedstroms. Soon after we had K-FLEX files, and then came the introduction of the Safety Hedstrom - something new and unique to the KERR Corporation. The Safety Hedstrom came about because doctors were having trouble negotiating very curved canals with standard instruments. The standard instruments would tend to not stay centered and ledging was often a result.
Safety Hedstroms are made from stainless steel, have a .02 taper, are available in ISO tip sizes #15-#55, and have the same cutting flute configuration as standard hedstroms. They are unique in their blunt, non-ledging tip design and their "Safe Edge" alteration of the cutting flutes along the longitudinal side of the file, which allows their safe use in curved canals without prebending. The plastic handle is flattened on the same side as the safe edge to identify exactly where the lessor cutting side should be turned in a curved canal. These files are used in a serial step-back method with the intention of creating a tapered preparation. Therefore each of the file sizes from #15-#55 is selected and used. The appropriate length of the file set must be chosen, but that is simple as length determination has usually been accomplished prior to commencement of shaping procedures. The intervals of the step-back indirectly determine the rate of taper imparted to the canal shape, with step-back intervals varying between 1mm for severely curved, thin roots down to 1/8mm intervals in straight roots with large terminal canal diameters. Radicular enlargement burs such as Gates-Glidden or Peezo burs are usually not needed to efficiently create shape in the coronal 1/2 of the canal.
Shaping Hedstrom NT .04 Taper files are selected and used in the same manner as the Safety Hedstrom files are used. .04 taper files have the same characteristics as the Safety Hedstrom except for the taper of the instrument. The taper is .04 instead of .02 and this doubling of the taper enhances the shape imparted to a root canal by this series of instruments, and effectively eliminates the need for coronal enlargement burs during preparation procedures. These instruments are available in tip sizes #15-#60. The .04 tapers are also used in a serial step-back method and by eliminating the coronal enlargement burs and files, a set of shaping instruments is reduced in number from 16 to 10.
The .04 Tapers are also made out of ultra-flexible Nickel-Titanium to give them the flexibility needed to negotiate severely curved canals. The tip sizing is standard ISO sizing which eliminates the need to learn another system of sizes. These instruments can be used by hand and with the M4 Safety Handpiece. The handpiece allows the instrument to float in and out of the canal and make the same dentinal cut as 4 to 6 physically taxing hand motions. The files are lightly bounced in the canal until they reach length or stop moving apically, and then are removed and replaced with the next file. When the file has reached its ideal depth in the canal, further in-and-out movement of the file in the handpiece will shape the canal less efficiently than simply floating the next larger file to it's place in the canal. If the file has stopped short of its ideal position in the canal, removal will often reveal flute spaces clogged with debris. Cleaning the flute spaces will often allow the same file to carve deeper into the canal. Refrain from aggressive apical movements in the apical third of canals, rather than forcing a file to place, it is always safer to move on to the next file and count on placing each instrument to its ideal position during the next recapitulation of the file series.
The second part to the Shaping Hedstrom NT System is the files of greater taper series of instruments. These instruments have tapers of .06, .08, .10, and .12mm. and are similar to the rest of the line in respect to their flute, Safe Edge, handle, and tip designs. The instruments are made of Nickel-Titanium for flexibility but are very different in their use and function.
There are only four tapers to choose from, .06, .08, .10, and .12. Unlike all other root canal instruments, a single taper size instrument is chosen and that instrument, alone, creates the entire preparation. No Gates-Glidden burs, and no serial step-back with 16 instruments. Because the instruments do not require serial preparation, each canal can receive an exactly predefined shape, enhancing the obturation result to follow. Each canal can have exact and adequate enlargement with a fuller shape 3-4mm's shy of the canal terminus.
These files have variable-pitch flute angles so that they are strongest at their tips and sharpest at their relatively large shank ends. Most have a maximal flute diameter of 1mm, causing their flute lengths to shorten as their tapers increase. The .06 taper has 14mm's, the .08 taper has 10mm's, the .10 has 7mms and the .12 has 5mms of cutting flutes respectively. Limiting the amount of coronal canal enlargement allows the clinician to impart as much apical resistance for as they need without risking weakening or perforating of the root. The parallel-sided shank of the file has a slightly reduced diameter to prevent it's binding in the canal.
Because of the radical taper of these instruments, they are best used in the M4 Safety Handpiece. The instrument selection process for these instruments is different than for serially-used instruments. Because a single file creates the shape through the length of the canal, the file chosen literally represents the final shape the clinician desires in a given root and root canal.
Just as a severely curved canal in a small root would usually suggest 3/4 to 1/2mm increments of step-back with a serial technique, the same root would ideally be shaped with a .06 taper file. Small roots (mandibular incisors, bicuspids with 2-3 roots, mesial roots of mandibular molars, and buccal roots of maxillary molars) with less curvature could safely receive a .08 taper or a .10 taper if there is little root curvature. Large roots (maxillary incisors, bicuspids with 1 root, distal roots of mandibular molars, and palatal roots of maxillary molars) would ideally receive a .10 or .12 taper shape depending on the terminal diameter and canal curvature.
The radically tapered files are used differently than any other. The appropriately tapered file is chosen for a given root and root canal. After the canal has been negotiated to its terminus and length has been determined, the shaping file is placed in the canal and the handpiece is activated. The file will eventually stop its apical movement and it should be removed. If it is clogged with dentinal debris, the file should be cleaned and reintroduced. In a canal of reasonable size, a single file will often move to terminal depth, completing the shape. If the file is not clogged with debris, a couple of workarounds can be used here. Our strategy is to change to a file with a narrower taper. Usually the less tapered file will move further into the canal, possibly to length. If the less tapered file goes to length, the more tapered file originally tried will usually then go to length. If the less tapered file goes to length, the more tapered file originally tried will usually then go to length. If a less tapered file meets resistance short of length, a series of four K-FLEX, K-Files or Safety Hedstroms larger than the current terminal file can be used in a serial method to very quickly create a canal of reasonable size.
In a curved, narrow MB canal, the procedural flow would go like this: #15 file to length, .06 taper taken to midroot length before stopping. After the use of a patency file and irrigation, use a #20 file 1mm short, #25 file 2mm short, #30 file 3mm short and a #35 fully 4mm back. The .06 taper file will then usually go to within 3-4mm of the terminus. With nearly all of the shaping in the canal completed, it is usually easy to accomplish the apical preparation with the hand files fitting in 1/2 mm increments of step-back. The .06 taper file will then go near full length.
These files should not be taken beyond terminal length in the canal as the apical constricture may be disturbed. These instruments, in spite of their tough NT alloy, are essentially single use instruments. If they receive light use, they can easily shape all of the canals in a multi rooted tooth. If they are used aggressively in a narrow canal, especially a curved one, the file should be discarded after shaping a single canal.
Autofit Gutta Percha and Autofit Absorbent Points have been designed with the same unique taper that the Shaping Hedstrom NT Instruments have. Because these points have this unique taper, fewer paper points are required for drying procedures and fewer gutta percha points are required for filling. Paper points are all 30mm's long and they are all rolled to a feather tip. They are available .06, .08, .10, and .12 taper file shapes. The points are selected to match the size of Shaping File used. If a .08 taper file is used, a .08 paper point and gutta percha point will be chosen.
The paper points are simply taken to, or beyod length in a canal shaped with a taper file of similar size. Because of the uniquely close fit to the canal shape, significantly fewer of these paper points are neede to dry canals. Their feather tips and their 30mm lengths allow ideal paper point length confirmation prior to obturation. The same size taper gutta percha point is placed into the canal until it binds. The point is grasped by cotton pliers at the reference point, measured and clipped to length. That's cone fit!
The gutta percha points will be 32mm long and .9mm wide at the large end. All will have a #25 tipand will match the taper of the shaping hedstrom instruments. These autofit points will be packaged with 50 points per box and will come in a box with 50 points of all one taper, or an assorted box with 10 points of each taper.