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.
Several different techniques are used for bleaching teeth at home. The whitening product may be placed in a mouthguard (or tray) that fits over the teeth, applied through adhesive hydrogen peroxide-containing strips that stick to the surface of the teeth, or âpaintedâ on the teeth in the form of a gel.