Teeth tend to change colour over time and they usually yellow with age. These changes can be reversed with a tooth whitening or bleaching procedure. Current modern techniques are very straightforward, and are usually done by you at home over a period of weeks with supervision and instructions provided by your dental team. Alternatively, you can have your teeth bleached at a dental surgery. Usually the chemical applied to the teeth is carbamide peroxide. This reacts with the acid on the teeth to change and become hydrogen peroxide, a powerful bleaching agent. The procedure itself is painless, but there are a few side effects that may affect some patients. The most common problem is sensitivity of the teeth and gums. If you visit a cosmetic dentist, prices can range from around £40 for a single tooth to over £500 for the whole mouth.