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.
A newcomer to the world of tooth whitening is known as chairside bleaching. This may require more than one visit, with each visit lasting 30 to 60 minutes. During chairside bleaching, your dentist applies either a protective gel to your gums or a rubber shield to protect the soft tissues in the mouth.