This is a very good question. Namely, the treatment is not finished by the removal of the fixed braces, since teeth would like to get back to their original places, where they felt all right for long years (i.e. into the position before the treatment). This is to be prevented by the so called retainers. Often these are not „night”, i.e. removable devices, but fixed rails, sticked on the inner surface of teeth. It is alwaysd the dentist who decides which one is to be applied.