A device for connecting at least one single-phase power supply line which, in particular, feeds the overhead line of a railroad track, to a three-phase power supply network. The pulse generation circuit generates rectangular waves at a frequency higher than those in the speech band, having a duty ratio such that the average voltage is equivalent to the bias voltage. Documents and sources of information can also be stored. The materials have improved properties that allow for advantageous restoration of molar and premolar teeth with the bulk filling technique.