When I had braces, I was wondering how my teeth move position when they're held in the jaw bone. I only thought about this because I was studying BIOL1001 at Sydney University. I asked my orthodontist and he told me to ask my tutor. I am sure he knows of course but didn't have time to explain such things to me!
Braces work by applying constant pressure on teeth, in the direction where we want it to be. The force stimulates the bone to resorb in areas of pressure. Where it is pulling away, more bone is created. This takes time to occur of course.
So even though the teeth are in solid bone, because of the biological environment, teeth are able to move in bone. This phenomenon only applies to real teeth however. Implants, cannot move within bone at all
Teeth are constantly moving throughout life. That is why after braces, if you want your teeth to stay perfect, you must wear your retainers.
Another thing to do with tooth movement is that if you have a tooth removed, over time, the opposing tooth will end up moving into the open space. As we age and use our teeth, they will get worn down and become shorter. The movement of teeth will accommodate the wear so that your bite stays balanced. .