Abstract: An irradiation device for photodynamic disinfection of teeth and gums in a mouth, comprises a mouthpiece which can be inserted into the mouth. The mouth piece has a U-shape approximating the dental arch and is equipped with one or more radiation sources for radiation in a wavelength range between 500 nm and 1000 nm. The irradiation device further comprises a handle piece which projects from the mouthpiece in such a way that it protrudes from the mouth after insertion of the mouthpiece, and a controller for actuating the radiation sources. The handle piece comprises a heat sink and the one or more radiation sources are mounted on a heat-conducting substrate which connects the radiation sources to the heat sink in a heat-conducting manner. Further described is a system comprising such an irradiation device and a rinsing solution.