New research reveals that the original Pretty Woman, actress Julia Roberts, has the best smile of all time.Eighteen years after her starring role as down-on-her-luck prostitute Vivian Ward almost half (47%) of the great British public voted for Julia as having the most beautiful and genuine smile around.

The poll was conducted by smile.co.uk, the internet bank.Surprisingly, second in the poll was ‘Mr Nasty' Simon Cowell (25%) with his ultra white smile and third was ‘Ugly Betty' actress America Ferrera, with one in five (21%) of the 3,000 polled voting for her smile full of braces.Leonardo Da Vinci's portrait of the Mona Lisa gained 5% of the vote to take fourth place in the poll of the best smile, while fifth place went to another star of the big screen George Clooney with 2%.

Conversely, super WAG, Victoria Beckham, topped the alternative ‘top five worst fake smiles', with US president George Bush coming second, Britney Spears third, Tony Blair fourth and Diana Ross fifth.

Psychologist, Donna Dawson said: ‘There are many different kinds of smiles, but the 'true', genuine, spontaneous smile is one where the mouth spreads in a relaxed way across the face and the eyes sparkle or soften, depending on the context and meaning of the smile.'

According to scientists, although fake smiles often look very similar to genuine smiles, they are actually slightly different, because they are brought about by different muscles, which are controlled by different parts of the brain.