Elastic ligatures can be single – each elastic goes around one bracket – or a chain made up of single elastics linked together. Chain elastics connect several brackets and are stretched when they're put on, so their job is to pull the brackets, and with them the teeth, towards each other. They are used to close gaps between any teeth in the same arch. On average, they close gaps at a rate of about 1 mm a month. If the gaps are larger, the elastic chain is replaced at every check-up for several months. As the teeth move towards each other, the end of the archwire may start to poke out behind the last bracket and injure the lining of your mouth. If this happens, you'll need to come and see us so that we can sort out the discomfort.
This answer is for general information. Your own case needs an examination by an orthodontist.