This fixed appliance is used in orthodontics to create more space in the jaws during growth, to accommodate teeth. It works by separating the two bones of the upper jaws which are connected at the roof of the mouth by a suture. The best time to use this appliance is when you are still growing before the upper jaw bones become connected permanently. The appliance must remain in your mouth for about 2-4 weeks during expansion, and for about 4 months afterwards to stabilize and reduce relapse.