The safest route is to choose a small bottle in the mid strength range and test it. From there you can determine the strength of concentration and go higher or lower. Remember that if your gums or your tooth are being irritated or hypersensitive you can choose the lower grades but then the desired results will take longer to manifest. 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. 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. Additional application of fresh bleaching gel could be opted depending on the development of the treatment and how the teeth have whitened. Extrinsic staining and intrinsic staining are the two basic types at which the teeth develop stains and discoloration. Extrinsic stains are developed in the surface of the teeth that resulted from the accumulation of food debris and color. 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. Buy the desensitizing toothpaste. This is one good investment if you want to take teeth whitening seriously. This can be used before and after using the teeth whitening toothpaste. The use of this product will limit the sensitizing effects. What are listed above are some things that should be kept in mind when looking for a teeth whitening toothpaste. The paste can be used as well in the bleaching and at the same time best used when maintaining that shiny white teeth. But be reminded that this product will not work to change the natural color of the teeth that has been overly exposed to the fluoride during its development. In theory, what makes the teeth whitening toothpaste works are its major ingredients.