I can't find the jewelry website where I read about this originally, but here is another:
"Many unfortunate silver jewelry owners stumble on the “ol toothpaste method” when looking to find cheap/easy ways to clean their silver jewelry. Sadly, what’s very unclear is that the same chemical used to keep your teeth clean can eat at your fine jewelry.
This is especially true when talking about silver, which is a very sensitive metal. The damage that toothpaste can cause may be so severe that only a professional jeweler will be able to fix it. Toothpaste will also scuff the surface on amber, opal, turquoise and other soft stones resulting in the fine polish to be permanently marred."
https://blog.ice.com/2014/09/24/toothpaste-2/
Edit: Pandora site talks about this as well:
http://www.pandora.net/en-us/universe/jewelleryguide/care