A tooth treatment device 10 comprises a body portion 11 which houses a battery 22, a gas cylinder 15, a power supply circuit 21 and a plasma generator 20 comprising a pair of electrodes 18, 19. The device also comprises a detachable applicator portion 12 and an elongate duct 14 extending from the generator 20 for conveying the generated plasma to an outlet and then onto a treatment area. An annular electrode 25 at the outlet of the duct 14 is connected to the power supply circuit 21 via an elongate electrical conductor 26. The outlet electrode 25 acts to conduct electrons in the generated plasma away from the emerging plasma plume, so as to decrease the electric current of the plasma plume and help avoid any sensation caused by the current flow. A circuit 17 may be provided for measuring the current flow from the electrode 25, the power supply circuit 21 being arranged for adjusting the power supplied to the pair of electrodes 18, 19 depending upon the measured current. The electrode 25 may also form a valve.
