Why smiling too widely can be a social handicap

Julia Roberts is known for her wide smile, but according to scientists she could appear more successful by toning it down. Photo / AP

By Sarah Knapton

Smiling too widely can be social handicap, scientists have said, after discovering the secret formula for a winning grin.

The most effective smiles hit a 'sweet spot' that is not too wide and avoids excessive tooth exposure, say scientists.

Researchers tested the reactions of 802 volunteers to a series of computer-generated 3D faces with varying kinds of smile.

Each expression was altered by varying mouth angle, teeth visibility, and the breadth of smiles as well as their symmetry.

Participants were asked to rate smiles based on effectiveness, genuineness, pleasantness and perceived emotional intent

The most "successful" smiles achieved an "optimal balance" of teeth, mouth angle and smile extent.

In fact it's best to keep the angle of lips at 13-17 degrees and width of smile to between 33 and 62 per cent of distance between pupils.

Symmetrically developing smiles also gained a more positive response.

Dr Nathaniel Helwig, of the University of Minnesota, in the US, said: "We define a 'successful smile' as one that is rated effective, genuine, and pleasant in the colloquial sense of these words.

"We define a 'successful smile' as one that is rated effective, genuine, and pleasant in the colloquial sense of these words.

"We found that a successful smile can be expressed via a variety of different spatiotemporal trajectories, involving an intricate balance of mouth angle, smile extent, and dental show combined with dynamic symmetry.

"These findings have broad applications in a variety of areas, such as facial reanimation surgery, rehabilitation, computer graphics, and psychology."

The research was published in the Public Library of Science ONE.

This article originally appeared on the Daily Telegraph.