At the end of your orthodontic treatment you will be provided with a retainer which may be a removable brace, a fixed retainer or a combination of both.
A removable retainer needs to be worn for 2 days full time, then every night in bed for at least a year and after this at least 3 nights per week long term. This will prevent the teeth moving back to their original position.
A fixed retainer is a wire cemented to the back of the upper or lower teeth. Fixed retainers are left on indefinitely unless they break or cause damage to the teeth or gums.