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.
A RealAge answered. How long you will need to use teeth whitening trays depends on the stains you are trying to bleach and how white you want your teeth to become. On average, you wear trays for a few hours each day for one to two weeks.But some people with severe stains may need to wear the trays for longer than that.ow long you will need to use teeth whitening trays depends on the stains you are trying to bleach and how white you want your teeth to become.