Yellow teeth can be a sign of heavy metals like cadmium. I wonder if the oil pulling brings heavy metals to the surface and then slowly clears them out. I believe that I detox heavy metals in waves. That they don't all come out at once. I have noticed my teeth going thru stages where they get real white, then yellow again, but I'm not too overly concerned as I believe my body is just bringing the bad to the surface and slowly ridding itself of it. I've been oilpulling for over a year now and this is only my humble opinion.