If something happens to your retainers - like your dog eats it - order new ones right away, and wear your last set of aligners in the meanwhile to prevent relapse. 

If you are already wearing or are on the last step of your aligner treatment, then we strongly suggest you order another back-up set. It's always good to have another set of retainers handy. 

Life happens - and one thing you want to happen is to make sure your new straight smile stays that way!