Instrument fracture: mechanisms, removal of fragments, and clinical outcomes

Instrument fracture can be an unpleasant mishap during non-surgical root canal treatment. While most stainless-steel instruments appear to fail by excessive amounts of torque, the combined action of torsional stress and cyclic loading (i.e. fatigue, as a result of rotational bending, or repeated torsion) is responsible for the breakage of NiTi rotary files in use. Factors affecting the incidence and mode of failures include the instrumentation technique, use of torque-controlled motor, the dimension and surface condition of the instrument, rotation rate, radius (and, to a certain extent, angle) of canal curvature, and the presence of a straight-line access and a ‘glide path’ to the apical portion of the canal. If breakage should occur clinically, the patient should be informed of the incident and consideration should be given as to whether or not to remove the fragment. Managed properly, the presence of a broken fragment per se may not adversely affect the outcome of root canal treatment. This review examines the various aspects (including mechanisms, contributing factors, prognosis and management) of instrument fracture. Emphasis is placed on the separation of nickel–titanium rotary files and ways to prevent this in the clinical situation.