Actually the one I was referring to was a filling that developed decay under it.
You could see it all around the edges.
After taking the silver water for a couple of weeks and waiting for my appointment to come up to have the work done, I looked at it closely and it all looked like new tooth material.
It didn't really have any holes in it to fill back in.
But I have this other one where a piece of tooth fell out leaving a hole.
It was due to decay (too much maple syrup in my teas).
I started taking the silver water again and now that tooth is fine except for the hole which doesn't seem to have changed.