When I looked at the white space on reddit and tilted my head side to side, I was able to see it almost clear as day. Pretty neat.
EDIT: link >> http://en.wikipedia.org/wiki/Haidinger%27s_brush
I have mild recession of them gum and bone near my back teeth, which is strongly correlated with the heavy pressure I apply when brushing. I have used medium to hard bristles, which within months would mushroom out. If I learn a way to reverse gum and bone recession in this situation I will post another TIL.