My son has no metal in his mouth, but I do and I have been oil pulling for just over a year now. I think a lot of us here still have almalgams with mercury, but we OP anyway. Not having any Science to back this up, I think that OP is helping the situation by pulling toxins out, including metal.
A number of us have had different herx symptoms, Amalgams or not. Your client could possibly have herx symptoms, regardless of amalgams. I had two nasty boils after starting OP. You would know better than I, but isn't that a good thing, a sign of de-toxing?
Perhaps Molly will share what she knows about this.