1 concentration gradient The difference in the concentration of a chemical across a membrane. 2  cytoplasm The living substance inside a cell (not including the nucleus). 3  diffusion The movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration.
Not all stains can be lightened by over-the-counter or professional bleaching, and your dentist will be able to give you guidance. If you have sensitive teeth, gum disease or teeth with worn enamel, your dentist may discourage tooth whitening.
Whitening strips and gels: These over-the-counter, peroxide based products are applied to your teeth using a thin strip or a brush. Typically the product needs to be applied once or twice per day for 10 â 14 days to complete the bleaching process.