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.
Teeth bleaching products should only be used under the guidance of your dentist. The best way to whiten teeth is by feeding your body lots of healthy foods for strong bones, teeth and gums and omitting coffee, tea and sugary foods in your diet.