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.
No home teeth whitening product gets better reviews than Crest 3D Whitestrips -- and the best of the best, reviewers say, is the Professional Effects series. While the claim that it removes 14 years of stains may be a bit of hyperbole, the fact is that you will get noticeably whiter teeth if you use these gel strips.