A device for working on an interproximal space in orthodontics, in conservative treatments, and prophylaxis of teeth, able to be connected to an oscillating handpiece, the device comprising a file having a tool-holding structure and an abrasive plate, wherein said tool-holding structure is shaped in an arc and provided at ends of said tool-holding structure with two tubular portions, wherein said abrasive plate is stably fixed at both ends of said abrasive plate to said tubular portions of said tool-holding structure, said tool-holding structure being symmetrical and overmolded on said abrasive plate, and a shank for the connection to said handpiece, said shank being removably fixed to said file alternatively at any selected one of said two tubular portions, wherein said shank comprises an elastic tang for the connection to said handpiece and a gripping head extending in one piece at an end of said tang for engagement with any one of the ends of said tool-holding structure of said file, wherein said gripping head and said tubular portions of the tool-holding structure comprise a plurality of matching stable coupling means, and wherein said stable coupling means comprise said tubular portions of the tool-holding structure and a matching tubular seat of the gripping head having a vertical axis perpendicular to the tang, said matching tubular seat comprising a longitudinal notch in a position opposite said tang and being suitable for guiding the insertion of any one of said tubular portions of the file along the direction defined by the axis of the tubular seat, said stable coupling means comprising at least one annular recess and an annular ridge, matching one another, arranged perpendicular to the vertical axis of the tubular seat and to a horizontal axis of the tubular portions for an axial snap engagement.