I have never heard of that happening - I use the Utopia Silver skin anc scalp bar to brush my teeth with. It gets rid of plaque and gum disease. I would look first at the product. I also wonder if perhaps the silver might be getting into plaque? A bit of 50/50 hydrogen peroxide might help with the discoloration. If not, zeolite minerals would be the way to go - but I would wait and see if it does not pretty much clear on it's own, perhaps with an assist from the H2O2.
Did you know that teeth can remineralize and cracks can be healed? I would suggest a good source of trace minerals along with the things that are good for bone and teeth (calcium, magnesium, boron, silica, etc). If you try to remineralize teeth you must NOT use regular toothpaste - or the aforementioned silver skin bar either - as they all contain an ingredient that coats the teeth and prevents re-mineralization.