Look into the Galopagos Islands. That is where I got the info about bird beaks. There are limits to how their beaks will change, but they do change quite a bit. A birds beak is more like our bones than our teeth from this standpoint. Our bones will become thicker or thinner, more or less dense, from use, just like the bird beaks. I am not aware of human teeth going through that kind of change. That is natural selection. Your definition of natural selection in that sense would be "lucky guy". Not real scientific there.