While hydrogen peroxide acts faster, carbamide peroxide when left in the mouth for a time divides into urea and hydrogen peroxide that acts on the stains by the oxidation process. It gets into the spaces of the rods in the enamel of the tooth, lifts the stains and drains the stain out. Several repetitions of this and the teeth become as white as its original color. If it does, it is actually very negligible and so does not have adverse effect on the tooth. Sure there could be, in some cases, mild irritation and tooth sensitivity during the initial stages but these usually are gone after a few days of treatment. What basically it does though is change the color of the teeth superficially. When using teeth whitening plastic strips therefore, the person has to lower the expectation. Realistically, plastic strips are designed as a do-it-yourself-at-home remedy. Unlike teeth whitening trays that are designed by a dentist or a licensed practitioner to fit personalized requirements, the strips are for general use and therefore are designed to address every possible requirement without causing discomfort. What are the differences, if there are any? For those looking for answers, then the following resources will serve as a helpful guide in weighing the differences between the two. And the differences between the two categories are assessed using the following measures: Composition and the strength of the bleaching agent used. It takes time to get the desired results. And also do remember that if you are not helping yourself (think: smoking) then there is a big chance that the results will be delayed and may be minimal. Do take note that the bleaching action can be faster if you will also do your part in the teeth whitening process. Some of the risks that are likely to occur are sensitivity to touch, temperature and pressure. For persons with sensitive teeth though, toothpastes containing potassium nitrate are recommended. Even without specialty toothpastes, the sensitivity is usually over in two days. However, persons with recessed gums, faulty tooth restoration and cracked teeth are more likely to encounter shooting pains.