An endodontic instrument for preparing an endodontic cavity space, the endodontic instrument comprising: a shank configured for attachment to a motor to drive the endodontic instrument about a first axis; and a body extending from the shank by a length, the body being solid and having a working surface between: i) a shank end where the working surface and the shank meet and ii) a tip end, the working surface including two or more edges, at least a portion of the working surface being tapered such that the tip end has a diameter that is less than a diameter of the shank end, the working surface comprising a plurality of transverse cross-sections, each transverse cross-section having a center of mass and two or more sides, the working surface having a center of mass path defined by the centers of mass of the plurality of transverse cross-sections of the body, at least one transverse cross-section of the plurality of transverse cross-sections consisting of two edges and two S-shaped sides extending between the two edges, wherein the endodontic instrument is configured to be radially compressible between: i) an unconstrained configuration in which at least a portion of the center of mass path between the tip end and the shank end is offset from the first axis and spirals around the first axis along a length of the first axis, and ii) a radially constrained configuration in which the portion of the center of mass path is more aligned with the first axis than in the unconstrained configuration, wherein a cutting profile of the endodontic instrument is radially smaller in the radially constrained configuration than in the unconstrained configuration, and wherein the cutting profile of the endodontic instrument radially expands during preparing the endodontic cavity space, and wherein the center of mass of the cross-sections where the body of the endodontic instrument conjoins with the shank is offset from the first axis in the unconstrained configuration and substantially aligns with the first axis in the radially constrained configuration. a shank configured for attachment to a motor to drive the endodontic instrument about a first axis; and a body extending from the shank by a length, the body being solid and having a working surface between: i) a shank end where the working surface and the shank meet and ii) a tip end, the working surface including two or more edges, at least a portion of the working surface being tapered such that the tip end has a diameter that is less than a diameter of the shank end, the working surface comprising a plurality of transverse cross-sections, each transverse cross-section having a center of mass and two or more sides, the working surface having a center of mass path defined by the centers of mass of the plurality of transverse cross-sections of the body, at least one transverse cross-section of the plurality of transverse cross-sections consisting of two edges and two S-shaped sides extending between the two edges, wherein the endodontic instrument is configured to be radially compressible between: i) an unconstrained configuration in which at least a portion of the center of mass path between the tip end and the shank end is offset from the first axis and spirals around the first axis along a length of the first axis, and ii) a radially constrained configuration in which the portion of the center of mass path is more aligned with the first axis than in the unconstrained configuration, wherein a cutting profile of the endodontic instrument is radially smaller in the radially constrained configuration than in the unconstrained configuration, and wherein the cutting profile of the endodontic instrument radially expands during preparing the endodontic cavity space, and wherein the center of mass of the cross-sections where the body of the endodontic instrument conjoins with the shank is offset from the first axis in the unconstrained configuration and substantially aligns with the first axis in the radially constrained configuration.