An endodontic instrument includes a cutting portion having upper and lower ends spaced apart along an axis, a cutting surface extending helically along the axis, and a non-contact surface extending helically along the axis. A cross section of the cutting portion in a plane perpendicular to the axis has a non-circular circumference. The cutting surface extends about a first portion of the non-circular circumference, and the non-contact surface forms a linear segment that extends about a second portion of the non-circular circumference. The cutting portion can further include a second cutting surface extending helically along the axis, and a second non-contact surface extending helically along the axis.