Abstract: The present invention refers to a plasma jet device (30) for medical treatment of root canals (3) using an atmospheric pressure plasma. The device comprises a handle (40) and a probe (50) with a gas channel (54) and a first and second electrode (31, 32). The probe (50) has a first end connected to the handle (40) and a second end opposite to the first end being a probe tip. The first electrode (31) extends to the probe tip. The first electrode (31) is a hollow outer electrode and the second electrode (32) is an inner electrode extending at least along a section of the first electrode (31) inside the first electrode (31). The second electrode (32) except for a portion at its end is surrounded by a dielectric material (33). The probe (50) is adapted to be inserted into a root canal (3). The plasma jet device (30) is adapted to provide negative pulses at the second electrode (32) for producing the atmospheric pressure plasma at the tip of the second electrode (32).