A dental bleaching kit comes with a universal tray that fits over your teeth. You use a specially formulated teeth bleaching gel that helps remove stains through the process of oxidation. The tray helps ensure that this bleaching gel stays on your teeth and does not get onto your gums where it will cause considerable irritation and discomfort. The price of these teeth whitening trays ranges from $30-60 and they are very effective in the removal of moderate discoloration over a period of about two weeks-depending on consistency of use.