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.
Discolorations are generally responsive to bleaching procedures, and dentists can advise on how to whiten yellow teeth depending on your case. Your dentist can provide bleaching kits to take home and use over a period of time, as well as in-office bleaching procedures.