Teeth Whitening Strips are very popular and can be bought in any drugstore. They are made of plastic and stick right to the surface of your teeth. Like the trays, they are made to be worn for several hours. Because the strength of the carbamide peroxide is half the strength found in bleaching trays, many whitening strips can be worn overnight. They do take longer to achieve the desired results, but if you apply them faithfully, you should notice your smile getting somewhat brighter.