Retainers can be removable or fixed. In some cases, the retainers may be worn for a short period of time. In other cases, they may be worn indefinitely. The orthodontist will determine which type of retainers would be suitable and the amount of time your retainers should be worn. Removable retainers are made of plastic with a wire at the front, and they can be removed for cleaning. 'Fixed retainers' consists of a small piece of wire that is fixed to the back of your front teeth and have the advantage to removable retainers in that they are 'invisible'.