Barry Musikant

nickel-titanium utilization requires special precautions.  [Nickel-titanium instruments] should only be used to resistance and never be forced.  Limiting factors associated with NiTi include the inability to bypass or remove ledges, a steep learning curve, high expense, and the universal concern for file separation.

NiTi rotary files are no more susceptible to breakage than stainless steel so long as all principles of rotary instrumentation are strictly adhered to, clinicians understand and master the respective systems prior to clinical usage, and proper disposal schedules are developed for NiTi. Aberrant canal anatomy, instrument fatigue, and improper usage patterns can contribute to file separation. It is much more critical in a rotary technique to fully comprehend the canal anatomy of each canal.  For example, NiTi files should be avoided in canal systems where two canals come together, when a canal bifurcates or where there is an S curve.  During use, clinicians should continually observe for instrument fatigue, as overuse or abuse of files will predispose them to failure. How a file is used and the type of canal form it is used in are probably just as critical as how many times a respective file is used; for example, calcified canals will logically stress NiTi files more than patent straighter canals. Usage and constant monitoring is additionally important because these files need to operate at the proper RPM and in a consistent manner.

LICKMAN AND KOCH’S list of caveats shows how narrow the window for success is in nickel-titanium endodontics.  If canals were not curved, there would be no need for nickel-titanium.  Yet the greater the curve the more susceptible nickel-titanium instruments are to fracture.  Manufacturers recommend frequent replacement of rotary nickel-titanium instruments, but they do not shed light on the interactions between the canal and the rotating NiTi file that rapidly produce the defects in the instrument that lead to fracture.  It is an empirical rule to reduce the separation of instruments within the canals without truly understanding the causes of separation.  Innovative methods of controlling torque are being added to the technique because fractures still occur despite increased and highly expensive precautions.
    Another phenomenon is starting to appear: the rationalization of the entire problem of fractured files.  Articles have recently appeared that minimize the problem.  One paper states that if an instrument fractures in the tooth, the tooth will often heal anyway or a simple apical procedure will solve the problem.  An apicoectomy on a mandibular second molar in close proximity to the inferior alveolar nerve is not a simple apical procedure.  Nor is any apical surgery simple for the patient.  If endodontic failure occurs because the dentist who performed the procedure is not able to cleanse and seal a canal with a fractured instrument in it, the dentist may be responsible for that tooth and any restoration supported by that tooth even though the doctor informed the patient that the instrument had fractured in the tooth when it happened.

Progress?

RACTURING A SEGMENT of an endodontic instrument is no less a problem for  dentists today than it was 25 years ago.  Any suggestion to the contrary potentially  misleads dentists, reducing their ability to make wise decisions concerning the endodontic techniques they wish to use.  From a historical perspective, any attempt to mollify concerns about fractured instruments tends to make more acceptable the techniques that lead to fractures.  Making the formerly unacceptable acceptable is a definition of lowered standards.  Standards should not be lowered as a way of being less critical toward a new system.  Any new system should meet and exceed consistently held standards.  That is a definition of progress. 
    The advantages of manual and rotary nickel-titanium instruments must be balanced against their disadvantages.  The same principle applies to stainless steel instruments.  Deciding which type of instrument to use is not an either-or situation, but rather an effort to incorporate the advantages of NiTi with the advantages of stainless steel into a system that eliminates the weaknesses of both.  The result would be a new system that would benefit from the best of both worlds: it would cause no hand fatigue or canal distortion, and it would be predictable, controllable, simpler, far less prone to fracture, and significantly less expensive. 
    Advocates of rotary nickel-titanium techniques claim that there has been a paradigm shift in endodontics.  There has been a paradigm shift, but it is defined by the final result, not the methods by which that result is attained.