tooth whitening Tooth whitening can be carried out at home. Over time teeth can become stained and discolored. This is due to a number of causes, the most common being aging, drinking tea, coffee some fizzy drinks and of course smoking! The act of whitening is achieved though a bleaching process that lightens the discolorations on the tooth enamel. The system uses a mild solution retained in a custom-fitted appliance which is worn over your teeth.  The appliance or bleaching tray is filled with a bleaching gel and this fits over the teeth. As the active ingredient in the gel, carbamide or hydrogen peroxide, is broken down oxygen enters the enamel and dentin and bleaches the teeth. And so the color is made lighter. Current research indicates that whitening teeth with 10% - 16% carbamide or hydrogen peroxide under the supervision of a dentist is completely safe for your teeth and gums. Although almost everyone can get some benefit from tooth whitening it's important to not that there are some instances where treatment may not be as effective. Your dentist will give you a thorough examination to determine if you are a good candidate for tooth whitening. Ideally your teeth need to be  in good condition with few or no fillings. Normally you'll start to see results within 7 days with the maximum whitening effect occurring over the next 14-21 days. Possible Side Effects. Some people experience increased tooth sensitivity to cold during treatment. Others report discomfort, in the gums or in some cases a sore throat. These symptoms normally disappear within 1-3 days after stopping or completion of treatment. Previous white fillings in front teeth may need to be redone. Crowns ( or caps) and denture teeth do not bleach.  How long do the results last Some patients may need periodic re-whitening.