Obviously the more curved a canal is, the higher the probability of the file separating due to cyclic fatigue. Repeated bending of instruments in curved canals causes the metal to fatigue, leading the instrument to eventually fracture. The other cause of instrument separation is ‘cyclic fatigue’. Larger sized files tend to be more resistant to these torsional fractures as they don’t bind as easily in those “tight spots”. Excessive force on the file during instrumentation causes the tip of the file to lock in a “tight spot”. Torsional fracture is when the tip of the instrument locks in a canal while the shaft continues to rotate, inevitably leading to fracture (5,6,7). When NiTi files fracture, it is due to cyclic fatigue or torsional strain. When NiTi rotary is used correctly, it is significantly faster and more efficient in the instrumentation of the root canal (1,2,3,4,10). Flexibility is the hallmark of NiTi rotary, and it is this feature that allows it to overcome one of the greatest challenges of root canal instrumentation, namely following the sharp and unexpected curves in most canals.
NiTi files also have high elastic flexibility in bending and torsion as compared with stainless steel files. One of the unique characteristics of NiTi is its ‘shape memory’, allowing it to be deformed during usage and then return to its original shape if it is not stressed beyond its elastic envelope (13). If however the NiTi file is stressed beyond its elastic limit, it will break (8). This transformation usually happens when the metal is stressed, such as during the instrumentation of the root canal. NiTi is a ‘superelastic’ metallic alloy that, when flexed, undergoes an austenitic-martensitic transformation from its original structure making it extremely flexible (5,17,20,21). To fully understand the positive and negative aspects of this great technology let us first take a closer look at nickel titanium itself. The big disadvantage of this system is sudden file separation within the canal. With every great innovation however, comes a down side and NiTi rotary is no exception. This flexibility allows for navigation of the most complex and curved root canals. The extreme flexibility exhibited by these ‘heat treated’ nickel titanium instruments is the key (1,2,3,4,10). Where navigation of a curved canal with stainless steel instruments might be extremely difficult and time consuming, nickel titanium rotary, when used correctly, can allow for a seamless canal preparation. Stainless steel files became stiffer as the sizes increased. The beauty of nickel titanium is its flexibility and efficiency. That all changed with the advent of nickel titanium rotary instruments, and a torque controlled motor. This proved to be tedious and quite tiring for the practitioner. There was a time when one would spend multiple visits hand filing a canal with stainless steel instruments. While the file can be easily straightened with your fingers, it is not necessary as once they are inside the canal, the EdgeFile X1 will follow and conform to the natural canal anatomy and curvatures.There have been few innovations in endodontics as revolutionary as nickel titanium (NiTi) rotary. With this proprietary processing, EdgeFile X1 files may be slightly curved.
Take each reciprocating file to length only one time and for no more than one second.Irrigate and lubricate frequently the canal throughout the procedure.Clean the flutes frequently and at least after removing the files from the canal.
Do not force the files down canals, use minimal apical pressure.Straight-line access is imperative for proper reciprocating file use and endodontic treatment.Do not use EdgeFile X1 in a traditional rotary hand piece.Use only in an electric motor and hand piece designed for the WaveOne instruments.
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