Abstract: The dental instrument with handpiece comprises an intermediate section (4) containing a micromotor. A handpiece (1) with a head (2) carrying a tool (3) is plugged in the front end of the intermediate section (4) so as to form a unit block therewith. At the back end thereof, the intermediate section (4) carries an adaptor comprising a part (10) integral with said section (4), and a part (9) which may rotate freely in the part (10) about the instrument axis. Said part (9) receives the adapter (8) integral therewith, of a flexible sheath (7) which connects the instrument to a supply station and brings thereto, besides the power and driving flux for the micromotor, air and water for a jet (15) of fine water droplets in the direction of the work location, as well as a lighting through an optical fiber thereof, through conduits (6,11,12,13,21) contained in the sheath (7) and going through the adaptor (9,10) separately.