We fit these once the fixed appliances have been removed, to keep the teeth in their corrected positions for at least a year afterwards. Patients normally have a combination of an upper removable appliance and a wire fixed onto the back of the lower teeth, although this can vary.
Removable retainers are normally worn all the time for the first few weeks, and then on a part time (eg night time) basis. They can sometimes be in the form of a clear plastic splint like the patient in the top left picture is wearing. These are virtually invisible and very easy to wear, but are not suitable for every case and do break much more often.