You may have noticed that your retainer is not as white as it used to be. The material that retainers are made of will naturally turn yellow overtime, if they are not properly cleaned and cared for. Peroxide and baking soda will be less abrasive than regular toothpaste, when trying to remove stain. Using these products will decrease any wear on the appliance acrylic. If proper steps are taken to care for the retainer immediately after receiving it, you can avoid developing the stain on your appliance in the first place.
Fill up your retainer case with a denture soak or cleanser. Leave the retainer soaking for up to four hours. Remove the retainer and rinse it with water.
Brush your retainer thoroughly using a half-and-half mixture of peroxide and baking soda. Scrub areas vigorously, where the stain appears to be the heaviest.
Place the retainer into the retainer case at night when you go to bed. Follow the directions on the box of denture whitening solution. Soak the retainer overnight in the solution. Alternate this with the denture soak cleaner. Rinse the retainer thoroughly with water, before placing it back into your mouth. Repeat the process, until the stains are removed.
Using an ultrasonic toothbrush will make the removal of the stain easier.
Do not try to whiten the retainer with regular bleach.