I got this teeth whitening thing in the mail for free. Normally I don't do any teeth whitening stuff, except for the toothpaste that says it whitens. I was wondering if the at home whitening things are safe. I figure since I have it, might as well try it. It says it's 12% hydrogen peroxide. The full list of ingredients is propylene glycol usp, glycerin usp, hydrogen peroxide usp, carbomer, triethanolamine, flavoring. Any ideas or advice on this?