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.
In-Office Tooth Whitening. Teeth whitening done by your dentist can get teeth brighter faster. The bleaching solution is usually much stronger than at-home kits. Also, heat, light, or a combination of the two may be used to speed and intensify the whitening process. The most dramatic results -- teeth generally get three to eight shades brighter -- usually take several 30- to 60-minute in-office visits.