Compared to stainless steel instruments, Ni-Ti rotary instruments are more flexible. They could not only allow for a higher quality of root canal shaping and cleaning, but also decrease the working time when applied in the curved canals. But instrument fracture is still a major concern. Instruments separation may add to the difficulty of the root canal therapy, even lead to the failure of the treatment. Cyclic fatigue is the main mechanism for instruments fracture in clinic. Lots of factors influence cyclic fatigue of instruments including internal
and external factors. This paper reviewed cyclic fatigue of Ni-Ti rotary instruments in the recent years, with an emphasis on factors influencing cyclic fatigue.
