Abstract: The invention relates to a medical or dental-medical treatment (3) which at its rearward end has a coupling element (7) for coupling on to a matching coupling element (8) of a flexible supply line (2a), and in its forward region has a holder device (5) for a tool, the handpiece (3) being of a rearward and a forward handpiece section (3a, 3b) which are connected with one another by means of a plug-in connection (17) and are fixed on one another by means of a latching device (72) which has a latching arm (75) extending approximately axis-parallel and which is transversely elastically bendable, which latching arm is arranged on the one plug-in connection part (77) and is latched in its free end region with a latching element (76) arranged on the other plug-in connection part (80).