 Because mercury can be so dangerous, concern has been raised about amalgam fillings, the silvery cavity fillings in our teeth, because they do contain mercury and release a certain amount every day. Eating just a single can of tuna a week, though, is the equivalent to having how many mercury-containing fillings in our mouth, day in and day out. Less than 5, 5 to 10, 15, 20, 25, or more than 25. Now, keep in mind, you only have 32 teeth. One can a week is like living with 29 mercury-containing fillings. I don't know if you remember those old James Bond flicks, but basically, that means looking like this.