An application substance reservoir for a toothbrush is provided. The reservoir has a data carrier and may be filled with toothpaste or another application substance. An electric toothbrush is also provided. The data carrier of the application substance reservoir may contain, for example, information regarding the prevailing filling level of the application substance reservoir and the type of application substance. The electric toothbrush has a data receiver for reading the data stored in the data carrier, a data transmitter for writing to the data carrier, and a control unit which may display the filling level in the application substance reservoir or the particular application substance used.