Is it safe to have base metal crowns and gold in your mouth? i've heard of currents that are bad for health.

Galvanic current: Galvanic current occurs in the presence of two or more dissimilar metals in an electrolyte or saltwater environment. In certain instances it can occur in your mouth with two dissimilar metal crowns. I have never heard that this would be detrimental you your health. You can avoid this by having restorations made of similar materials.

Crown materials: Gold restorations have been around for many years and are considered completely safe. They are being used less and less for esthetic reasons as well as for their high cost. Semiprecious metals are less noble and may be of more concern depending upon their actual constituents. The use of base metals is generally frowned upon. I am not aware of a health risk due to production of electric currents.