Is it more effective and safe to finish root canal preparations with hand files or rotary nickel titanium files?
There are proponents on both sides of the issue. My empirical bias is that it is inefficient, fatiguing and risks iatrogenic events unnecessarily to finish root canal preparations with hand files. It could be strongly argued that rotary nickel titanium files (RNT) are the de facto standard of care for root canal preparation. I use K3 (SybronEndo, Orange, CA, USA) for its tactile control, flexibility, durability, cutting ability, and resistance to fracture. K3 is available in three tapers .02, .04, and .06 in various tip sizes 15-60 and as such, it can create larger than traditional master apical diameters.
Virtually always, irrespective of the curvature, if the proper precautions are taken, the clinician can take any canal in which a glide path has been created (the canal is open to the size of a #15 hand file) and then enlarge the canal with RNT up to the desired diameter. This requires elaboration. In clinical practice, a severely curved canal which is open and patent to a #6 or 8 can be enlarged initially though the use of a M4 safety handpiece (SybronEndo, Orange, CA, USA) which uses reciprocation. In clinician practice, the #6 or 8 hand file is placed into the canal to the estimated working length, interpreted most ideally from digital images (DEXIS, DEXIS digital radiography, Alpharetta, GA, USA) prior to treatment. With the file in the canal and the rubber dam on, the M4 is attached to the file.
With a vertical amplitude of about 1-3mm, the file is used with the M4 until it spins freely. Using the M4 in this manner can save the clinician a significant amount of hand fatigue and time. In essence, safely and efficiently, the canal which might not at first easily accept a #6 or 8 file can be enlarged to a #10 to 15 with this reciprocating action and do so with minimal risk of fracture. The hand files attached to the M4 can replace the often hand fatiguing enlargement of narrow and curved canals manually with an engine driven system that is simple, easy to use and very safe.
The M4 is attached to any electric motor with an E-type attachment. In my operatory, this electric motor is either an ELECTROtorque TLC (Kavo, Lake Zurich, Il, USA) or a TCM III (SybronEndo, Orange, CA, USA) at 900 RPM. After the creation of a glide path in this manner, RNT preparation can be completed.
Hand files used to shape the final prepared apical diameter are inherently problematic because such files easily deviate the canal path (i.e. create elbows, ledges, perforations and canal transportations of all types) and are hard to center predictably without specialized rotational techniques. Hand files of any size (above a #20) are inherently stiff and do not have the super elasticity of RNT files, their natural tendency being to straighten in the canal and cause transportations of all types. For example, taking a #35 hand file around a moderate to severe curvature is clinically challenging as aside from transportations, the files risk creation of apical debris that can prove challenging to remove.
In addition, using hand files in the apical third is challenging in that the needed taper of the canal apically must be developed most often in 1/2 to 1mm increments back up into the apical third of the canal. In essence, if the clinician takes a #40 for example to the apex of the mesial buccal canal in the mesial root of a lower molar they must then take a #45 to 1/2 to 1mm short of this length to develop taper in the canal and each chosen canal increment back from the MC must use one larger size instrument to create a tapering funnel in the apical third. While this can be done and was the technique of choice before RNT instruments, it is time consuming aside from the other challenges mentioned above.
Some might also argue that the risk of RNT breakage is too great with respect to profitability and liability. While in some respects RNT files are more expensive, they make the process of treatment much shorter than they otherwise would be and if used correctly, RNT breakage should be a very rare event. Using hand files well will take a substantial amount of time in all clinical cases relative to their RNT counterparts. For the clinician that refuses to employ RNT files at all or perhaps in the apical third, one consideration might be for them to try and utilize RNT files in the coronal and middle thirds and then observe, after glide path creation, if a RNT file is easily accepted into the apical third. If it is, the final preparation can be carried out with RNT files.
In addition, irrespective of whether one is using hand files or RNT files one cannot overstate the value of a surgical operating microscope (Global Surgical, St. Louis, MO, USA) in visualizing the emerging canal preparation. The SOM can alert the clinician if debris is accumulating in canals, whether the correct taper is being created or if a fin is present which needs removal.
In summary, using RNT files for canal preparation, especially in the apical third can allow the clinician to have fewer hand files in their sponge and still maintain all the capability needed to prepare all manner of clinical anatomy. In other words, for all practical purposes, it is not necessary to have hand files for reasons other than apical gauging (determining the initial diameter of the minor constriction of the apical foramen) and for initial negotiation, creation, and maintenance of patency and creation of the glide path.
I welcome your feedback.
Dr. Mounce has no commercial interest of any kind in any products mentioned in the article.
