Mechanisms of instrument fracture and removal

Root canal treatment is fundamentally dependent on root canal preparation. This phase of the treatment consists of cleaning and shaping the canal, and is a challenge particularly when shaping curved canals. 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.