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 makes a custom fitted plastic tray and sends you home with bleaching gel. Typically, results are seen within two weeks. Some products are used twice a day for two weeks, while others should be worn overnight for one to two weeks. Custom fit trays can also run between $300 and $2,000.