The way a tooth moves is an amazing process. When force is applied to the roots of the teeth through the brace the cells in the bone and tissues around the roots are stimulated.
Remember that a brace is made up of two main parts: the brackets that are bonded to the teeth and a wire that runs between all these brackets.
A pushing or pulling pressure is placed on the brackets via the tension in the wire that runs between the brackets. This pressure travels from the brackets into the teeth and down in to the roots of the teeth. This stimulates the body to change the structure of the bones around the teeth, allowing the teeth to move in the direction of that pull or push.
Naturally, there is a delay between when pressure is applied and when the teeth move. The time taken for teeth to move differs from person to person. At first, movement is very slow but then appears to speed up over the next few weeks. To a patient it can seem like movement has been very sudden and 'over night'.
Early in treatment, the orthodontist may use a flexible wire with less tension to gently start movement. Appointments could be scheduled anywhere from 4-12 weeks apart.
Later in treatment, as the mouth has become used to wearing the brace and the teeth are used to moving, a little more tension may be applied. Appointments may be scheduled 2-6 weeks apart.
There are many variables that may contribute to variations in treatment time. However, many patients that have similar problems will tend to have similar treatment times. On average treatment duration for comprehensive treatment can be up to two years in duration.
At the end of treatment you will need to wear a retainer. Remember that the bones around your teeth have been changed to allow your teeth to move. Those bones are soft. It will take time for those bones to go hard again and lock your teeth into their new position. So you must wear a retainer to hold your teeth in place while the bones are hardening again.