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.
Your dentist may suggest: 1  Putting a special bleach on your stained teeth and using heat (or heat and light) to start the bleaching action; or. 2  Wearing a custom-made mouthguard filled with a special bleach for part of each day; or.  Brushing with a special bleach mixed in toothpaste.