The head (4) has a support unit (8) for movably supporting a plate-shaped bristle carrier (7), which carries external and inner bristles e.g. bunch of bristles. Each external bristle exhibits a height larger than the inner bristles, such that a central recess is formed in a working surface (34) defined by free ends of the external and inner bristles. The central recess exhibits a groove-shaped base that is curved in a direction. A cascaded level-spring is provided between the central recess and the external bristles.
