A perfect smile depends not only upon the whiteness of a person’s teeth but a number of other factors also, say scientists. Dr Nicholas Davis of Loma Linda University School of Dentistry in Southern California says that right size and width of each tooth, right curve, colour and shape of the teeth, and the overall width of the mouth are the factors which together contribute to a lovable smile.

He feels that the whiteness of the teeth should match the whites of the eyes, else the smile will stand out too much and detract from the rest of the face. "One of the first things about a smile people notice is the colour," the Daily Mail quoted Dr Davis, as saying.

"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," he added.

Describing his formula for a perfect smile in the journal Dental Clinics of North America, Dr. Davis said that the ideal width of a smile should not be less than half the width of the face, and both upper and lower lips should be symmetrical each side of the mid-line of the face.

He says that the top row of teeth should be dominant, while very little should be seen of the bottom row. Dr. Davis also says that all the teeth on display should be straight, and there should not appear any signs of restoration work.