Braces do not change teeth. They use the teeth to transmit instructions to the bone of the jaw for the bone to move the tooth. It is the bone of the jaw that changes shape.
The reason this happens, is that the tooth is not held directly by bone. It is attached to the bone by a very short ligament which surrounds the root of each tooth. These ligaments hold many cells, some of which move bone out of the way when pressure is placed on them. Also, there are cells which build new bone when they are placed in areas of tension. The braces transmit the tension and pressure to ligament, which activates the body’s cells.
All of this is a normal and natural ongoing physiologic process. Processes that are normal and natural for your body do not hurt. When braces are adjusted, they produce a little too much pressure. That is why the teeth are sore. As the pressure drops into the physiologic range, the teeth stop being sore. That is when they are moving.
We strive to keep the pressure on the teeth constant and with-in the physiologic range. This allows teeth to move as fast as the body will allow. It is the physiology of your body which sets the speed at which teeth can be moved. On average the bone will allow 1/2 mm to 1 mm of movement per month.