An endodontic instrument (200) includes a cutting portion having upper and lower ends (202, 204) spaced apart along an axis, a cutting surface (206) extending helically along the axis, and a non-contact surface (210) 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 (206) extends about a first portion of the non-circular circumference, and the non-contact surface (210) 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 (306b) extending helically along the axis, and a second non-contact surface (310b) extending helically along the axis.
