What makes the perfect smile? The answer to this question depends on your own idea of perfection, and can be defined differently around the world. However, in this day and age, dentistry is playing a larger role in people's lives and as a consequence there is greater desire to achieve the 'perfect smile'.

A self portrait of Madame Vigee Le Brun showing a white tooth smile. Albeit the outrage caused in 1787, it became a signature gesture in her portraits.

EUROPE: Mouth closed or mouth open?

Colin Jones set out to challenge the idea of the smile being a timeless, universal manifestation of genuine positive emotion in his book The smile revolution in eighteenth century Paris.

Jones compared the 'snooty, aggressive, closed-mouth smile' of 1700 Paris with the 'open mouth, white-tooth smile' of the 1780s. The revolution, he believed, related to advancements in dentistry at the time as well as societal ideas about respectability and the appropriateness of emotional expression.

Kate Middleton. Kate's orthodontist, Dr Fillion, whose craftsmanship takes on the approach of a European definition of a perfect smile. He believes that a perfect smile should show imperfections and be less white than the American approach.

By the mid-eighteenth century, the smile was changing from an outlandish display of emotion to a romantic and core human attribute. Around the same time, dental hygiene was improving, causing the practice of 'tooth removal' to fade.

Perfect imperfections

Dr Fillion, aka The Artist, is a world renowned orthodontist, whose 'artwork' is thought to take on a European's definition of a perfect smile.

Unlike the Americans' 'piano keys', the European's perfect smile is asymmetrical, and seeks only to rectify individual teeth with minor changes. This is done by using braces to straighten the teeth without changing the natural shape of their teeth.

The process might also involve grinding and polishing of the enamel or adding porcelain veneers, but all done in a very delicate manner.

A portrait of Madam Lisa Giocondo drawn by Leornado Da Vinci, titled Mona Lisa. The painting was produced in the early sixteenth century when it was uncommon for people to show their teeth when smiling.

Europeans believe that perfectly symmetrical teeth and absolute alignments are not a dogma or doctrine for a perfect smile. Other well-known figures who don the European perfect smile include the Duchess of Cambridge Kate Middleton, whereby the beauty of her smile lies in the perfect imperfections of her teeth.

Expectation vs reality

In the younger generation, there has been a shift from a natural look to the more Hollywood-smile style recently and Dr Mervyn Druian of the London Centre for Cosmetic Dentistry says it is not unusual for people to insist on a whiter shade than is suitable.

Ricky Gervais was criticised for his teeth by an American journalist after appearing on the movie Ghost Town. Credit: © Thekla Clark / Contributor/Corbis Historical; Leonardo da Vinci; Samir Hussein / Contributor/WireImage; Noam Galai/Contributor/Getty Images North America

'I had one patient who complained because the whiteness wasn't as white as his shaving cream. It drives me crazy. But in the end, you've got to do it,' said Druian.

Just 3% of people in the UK have had teeth-whitening, lagging behind the 14% in the USA, although the number in the UK is increasing.

British comedian Ricky Gervais is the first to admit that his teeth are neither white nor straight and Americans mistakenly think he wears bad false teeth for comedic purposes. He stated that one American journalist was horrified that he could have such horrible real teeth.

'It's like the biggest difference between the Brits and the Americans, they are obsessed with perfect teeth,' said Gervais.