Manufactured from nickel-titanium alloy with Controlled Memory (CM) heat treatment, HyFlex CM files are extremely flexible and more resistant to cyclical fatigue. Therefore the files can follow the anatomy of the canal very closely, reducing the risk of ledging, transportation or perforation. Furthermore, the files can be pre-bent, similar to stainless steel files. Particularly in root canals with abrupt curvature, this can help avoid creating steps. This form adaptation can be reversed quickly by heat treatment returning the instruments back to their original shape. Visual control after thermal treatment provides the opportunity to verify safe continuation of file use.