An interdental treatment device comprises a generator 16 for generating a non-thermal gaseous plasma at a temperature suitable for use in oral treatment and an applicator 18 of the non-thermal plasma. The applicator 18 may comprise a hollow needle member for directing a jet of the non-thermal plasma interdentally. Alternatively the applicator 18 may comprise an interdental brush having a hollow head for receiving a non-thermal gaseous plasma, the head having at least one lateral opening for the discharge of the plasma. The generator 16 and applicator 18 may both form part of a hand-held device 10 having its own gas supply in the form of a capsule 12 containing pressurized gas and its own power supply in the form of a battery 20.