Let’s Get Technical: How Do Braces Move Teeth?
It's assumed that the brackets move the teeth, however pressure is actually created by the archwire. After the wire is placed along the uneven path of the misaligned teeth, it tries to straighten out to resume its original shape-bringing the teeth with it. The wires are very flexible to start out with and are traded out during the course of treatment for stronger and stronger ones.
If that wasn't technical enough, try this: when pressure is applied to a tooth, the periodontal membrane, which is the supporting ligament surrounding the root of the tooth, stretches on one side and compresses on the other allowing the tooth to loosen. This stimulates the bone in the path of movement to break down so the tooth can move in that direction. Then the bone behind the tooth rebuilds after the tooth moves out of that place to support it in its new position. This process is called bone remodeling.
People also assume that the faster the teeth move the better. That's not always correct. While it only takes 72 hours for the bone to break down in the path of the tooth movement, it takes 90 days for it to rebuild around its new position and 10 months to stabilize it! If you move teeth too quickly, you risk losing them and if you don't wear your retainer enough after your braces come off, your teeth won't stay in their beautiful new position and will relapse.