The external part of the teeth, the porcelain layer, is colorless. The color of the teeth is determined by the color of the teeth that are under the porcelain layer. The whitening agents penetrate through the porcelain layer in order to whiten the teeth under it. It is very important that the whitening agents do not deteriorate the porcelain layer, because that would leave the teeth unprotected and with a dull appearance, without transparency and finally lifeless.
The loss of color of the teeth can be classified by intensity gradations and the agent that caused the darkening of them. If the spots are superficial, like spots caused by nicotine for example they can be removed with a simple cleaning treatment. For more profound discoloring it is necessary to use specific whitening products.
The substances that are being used nowadays are carbamide peroxide and hydrogen peroxide in various concentrations and formulas. Both substances are being considered safe if the doses and the durations are correct and always under the supervision of a dentist. These products generate a chemical reaction which causes the teeth to whiten without affecting their structure. The whitening effect is permanent, although the teeth can get darker again after a certain time, because they are being subject again to the substances that darken the teeth. Generally speaking it may be necessary to repeat the treatment after a few years.