Nickel-titanium rotary instruments are widely used in clinic because of their super flexibility. Compared to the stainless steel instruments, they can keep the originality shape of canal and favorable taper and achieve better therapy result with higher efficiency. But the unavoidable problem is that nickel titanium rotary instruments are easy to fracture without any visible signs. Fractured instruments are a definite hindrance to the goals of cleaning, shaping and filling root canals, and they may adversely affect the outcome of endodontic treatment. There are a lot of factors that influence fracture of nickel-titanium instruments. This article reviewed the development of studies about factors in recent years.
