Not so amazing perhaps when you consider all of the bacteria you have in the mouth. One thing you want to avoid is using silver at or near the same time as any kind of saline solution, including the common salt water gargles you would ordinarily use.
The FDA has made quite the issue and scare tactic of warning about silver making people turn blue, but the truth is that it has never happened with true colloidal silver and a very tiny number of incidences have ever been reported. The two most famous were caused by someone using large particle ionic silver suspended in gelatin and labeled as a colloid and someone who made silver at home in salt water (a saline solution) and thus ended up producing silver nitrate, which they drank by the gallons.
True colloidal silver never, ever has such a problem - such as the silver made by . . . . . . well, you know who I am talking about - lol!