Most of us would like to have a gleaming white smile, filled with teeth that would make a Hollywood actor proud. Studies show that 18-52% of people are dissatisfied with the colour of their teeth.

In countries such as the US, tooth whitening is one of the most commonly requested dental procedures, while the British are often the butt of jokes about yellowing gnashers. Rows of perfect teeth beam out from magazines and cinema screens around the world.

It is hardly surprising then, that we tend to assume that white teeth are not only attractive, but healthy. The hue of our teeth depends on their intrinsic colour, influenced in part by our genes and our age, combined with stains from smoking, eating, drinking and taking certain medications. As you get older your teeth often become yellower as the enamel begins to wear away, exposing the dentine beneath.

Green fur

Stains then overlay the yellowing teeth, with foods such as tomato-based sauces and coffee leaving behind coloured compounds called chromogens, while bacteria or fungi can cause green, greyish, furry looking stains.

Many of the experiments on tooth colour have been conducted in laboratory test tubes, rather than in the mouths of living people. Often cows’ teeth are used because they give researchers with a larger surface area to study, but sometimes extracted human teeth are tested too.