A protective rubber dam is them placed in the gum to protect it from irritation when the bleaching gel is applied. The bleaching gel is then applied to the teeth and then rinsed off after at least 15 minutes after which another application of the bleaching gel will be applied and kept in the mouth for approximately the same period of time. While superficial stains and discoloration could be removed by prophylactic cleaning and brushing, there are stains that are a little more stubborn and could accumulate between the spaces of the tiny cracks in the tooth that would need bleaching to remove the stains. When the stains are not effectively removed and stays on the teeth for a period of time, this could penetrate deeper into the dentin which could require more involved methods. Since carbamide peroxide is only half the strength of hydrogen peroxide, the visible effect will take about two weeks of continued use, much longer than bleaching trays that contains hydrogen peroxide and in-office treatments but because it is, teeth whitening strips is gentle and comfortable to even those with very sensitive teeth and gums. When shopping for this product, do keep in mind that the crowns, the fillings and the veneers will not be affected by the whitening action of the paste. Complement the use of the whitening toothpaste with the services of professional teeth cleaner. This is something that you would like to do if you want to achieve the best results for your teeth. For this two main whitening agents are used, the hydrogen peroxide which is a strong bleaching agent for many bleaching purposes and the much milder carbamide peroxide. Although hydrogen peroxide is usually the bleaching agent used in in-office procedures it could also be used at home for those who do not have hypersensitivity in the gums or in the teeth. When using hydrogen peroxide for example, the concentration of the mix that is recommended at the back of the bottle should be adhered strictly if not less than what is recommended just to test it out. While studies have shown (Kugel et al) that the effect of peroxides at decreasing the tooth enamel is very insignificant, it nonetheless tends to make the teeth more sensitive for some time and when the proportion of the mix is on the strong side, the mix could result to painful gums and cause irritation to the surrounding tissues inside the mouth.