A plastic-injection tool capable of producing a brushing or combing device molded by plastic injection comprising a plurality of bristles on a support, disposed according to geometrically regular patterns, each bristle having a base attached to the support, a flexible main portion extending on a longitudinal axis (XX') substantially orthogonal to the surface of the support at its anchorage point, and a free end, with the majority of bristles further comprising: - a main portion defined geometrically by travel of a straight generator (g, g') around the longitudinal axis (XX'), the distance between the generator and this axis (XX') being at any point less than 0.5mm and the angle (α) between the generator and the longitudinal axis (XX') being less than 2° at any position around said axis (XX'); - a free end defined by a transverse surface intersecting the longitudinal axis (XX') of the main portion; and - a total length lying between 1.5 and 15mm, with said tool comprising at least one block assembly in which cavities capable of molding a plurality of bristles are hollowed out, - the block assembly comprising several steel plates which are assembled permanently during use of the mold and able to be dismantled periodically, - the block assembly comprising at least one row of cavities each intended to form the main portion of a bristle, machined on either side of the surface separating two adjacent plates (212a, 212b), - a closing-up element (224a to 224c) in the form of a plate or a bar, is disposed at the end of at least one row of cavities, in order to form the free end surface of the bristles, characterized in that - a space of calibrated thickness, of between substantially 0.005 and 0.050mm, is made between the plates forming the main portion of the bristle and the plate or the bar (224a, 224b) forming the free end surface of the bristle, so as to allow the air present in the cavity to escape at the time of the injection whilst avoiding leakage of plastic, - an ejection mechanism (223a, 223b) is provided for extracting the device from the cavity after solidification of the plastic by exerting pressure on the support parallel to the main axis of at least some of the plurality of bristles. - a main portion defined geometrically by travel of a straight generator (g, g') around the longitudinal axis (XX'), the distance between the generator and this axis (XX') being at any point less than 0.5mm and the angle (α) between the generator and the longitudinal axis (XX') being less than 2° at any position around said axis (XX'); - a free end defined by a transverse surface intersecting the longitudinal axis (XX') of the main portion; and - a total length lying between 1.5 and 15mm, - the block assembly comprising several steel plates which are assembled permanently during use of the mold and able to be dismantled periodically, - the block assembly comprising at least one row of cavities each intended to form the main portion of a bristle, machined on either side of the surface separating two adjacent plates (212a, 212b), - a closing-up element (224a to 224c) in the form of a plate or a bar, is disposed at the end of at least one row of cavities, in order to form the free end surface of the bristles, - a space of calibrated thickness, of between substantially 0.005 and 0.050mm, is made between the plates forming the main portion of the bristle and the plate or the bar (224a, 224b) forming the free end surface of the bristle, so as to allow the air present in the cavity to escape at the time of the injection whilst avoiding leakage of plastic, - an ejection mechanism (223a, 223b) is provided for extracting the device from the cavity after solidification of the plastic by exerting pressure on the support parallel to the main axis of at least some of the plurality of bristles.