Objective: To analyze the clinical fracture of nickel-titanium instruments and its causes.
Methods: 68 Profile and NiTiflex files broken during the clinical root canal instrumentations in two years were collected. The analysis was carried out regarding the relation between the broken files and the distribution in the teeth, canal, degree of curvature of canals, and the relation between amount of the broken files and the period.
Results: The majority of the clinical fracture of nickel-titanium instruments were flexural fatigue which frequently occurred in molar, the midpoint of the curvature, canal with curves > 30 degrees and very complex canals. Amount of the broken nickel-titanium instruments in the first year was twice than that in second year.
Conclusion: The fracture of nickel-titanium instruments is closely related to the anatomy of the root canal, the operator's experience and the usage of instrument and so on.