Removable retainers are made from a thin, clear, plastic-type material and are custom made to fit closely over your teeth once your orthodontic treatment has been successfully completed.
They are usually worn on a full time basis initially (except for meals, sports, swimming or when brushing your teeth) and then when asleep in bed each night in the long term.
Removable retainers do deteriorate through natural "wear and tear" and need to be replaced in time.