If you already have a retainer, a nightguard, or a set of aligners, there's no need to purchase the entire whitening kit from CustMbite. Instead, you can simply grab yourself a bottle of CustMbite Gentle Whitening Foam for just $19.99 and use your existing oral appliance to apply it at night. For example, you might have already purchased a CustMbite Night Guard to deal with teeth grinding. Since this nightguard is already personalized to your unique oral cavity, all you need to do is fill it with Gentle Whitening Foam and you're all set. With that being said, CustMbite's Teeth Whitening Kit is only $39.99, and it comes with a fresh set of trays, Gentle Whitening Foam, and Whitening Gel for plenty of customization options. So for just a little more, you get plenty of additional value. Better yet, it also comes with a money-back guarantee for added shopping confidence.