Formula for the perfect smile

And the secret? Hide yourgums, hold the bleach and don't show your bottom teeth,according to the latest research

Dentists and researchers have come up with the formula for the perfect smile, from the size and width of each tooth to the curve, colour and shape of the teeth, and the overall width of the smile.

Those pursuing perfection are advised to hide their gums, hold back on the bleach, cover the bottom teeth and set their lips at just the right angle.

"Everyone wants the perfect smile – and Jessica Simpson is the one we get asked to reproduce the most," says Dr Nicholas Davis of Loma Linda University School of Dentistry and a California dentist. His report on the design of a beautiful smile appears in an industry journal, Dental Clinics of North America.

"Creating the ideal smile involves taking all kinds of dimensions and factors into consideration, including the shape and size of the face, the lips and gums, as well as the teeth," he says.

According to the report, colour is important, and too many are now bleached too white. "One of the first things about a smile people notice is the colour," says Dr Davis. "People are bleaching their teeth and many times they do it beyond what is natural. The teeth should be the same colour as the whites of your eyes. If the teeth are too white, they become more dominant than the eyes."

There are strict mathematical ratios governing the ideal smile, says Dr Davis. Its width should be no less than half the width of the face at the same height and, for the best effect, both upper and lower lips need to be symmetrical each side of the mid-line of the face.

All of the visible teeth should be straight, with no visible signs of restoration work. The top teeth need to be dominant, with little seen of the bottom set. Those either side of them, the laterals, should be 61.8 per cent the size of the bigger teeth. The next teeth along should be 61.8 per cent of the laterals.

The width of the central teeth should be 80 per cent of the height, and the length should be around one 16th of the facial height.

Exactly how long the central teeth should be varies, but they are too long if they interfere or impinge on the lower lip. The back teeth should diminish in size from front to back.

Gums are important, and to avoid a horsey smile, very little should be seen. Their colour is critical, and should be a healthy pale pink.