Endosseous screw (1) for fixing a plate (102) to a bone site (300), comprising an at least partially threaded shaft (2), insertion means for inserting the screw into a bone site and a distal portion (33) provided for engaging said plate to fasten it to said bone site and comprising a head (3) having facets (30) defining an external peripheral profile provided for engagement with a tubular manipulating wrench, to allow the screw (1) to be extracted from the bone site (300) into which it has been inserted, wherein the facets (30) are curvilinear and the external peripheral profile defined by same facets (30) has a convex barrel-like shape, in order to allow a stable coupling between the tubular manipulating wrench and said profile, which is maintained during the untightening phase of screw from plate, even when said tubular manipulating wrench is oriented in an inclined direction with respect to a longitudinal axis (x) of the endosseous screw (1).
