Most patients would like to believe that once their teeth are orthodontically straightened that they will stay that way, often this is not the case. Post orthodontics, patients who do not wear their retainers are at risk of unintended drifting of their teeth. To keep teeth their straightest, retainers should be worn for life. Most modern retainers will not only keep teeth aligned but also will offer some protection from wear.
If the retainers are made with a vacumn former, then they often can be used for home bleaching as well. Just place the bleaching solution on the inner front surface before bed and take them out in the morning. The teeth will look whiter! In my practice we recommend an 16% Nite White solution, but many different formulations work well.