Depends on the type of grinder. A saddle-type quern absolutely puts enough rock into the flour to degrade teeth, as seen on ancient egyptian remains.

When I was a child my parents did a brief experiment grinding our own flour with a cheap grindstone. I can clearly remember the sensation of the bits of stone in the bread.

It is possible to make flour without this problem? Almost certainly! But this n=1 anecdote demonstrates it’s a thing that can happen.