Less is more when it comes to flashing a perfect smile
You're never fully dressed without a smile - but be careful not to overdo it.
New research has found that an exaggerated smile could actually be something of a social handicap, and that it can make you appear less 'genuine' or 'pleasant'.
Scientists have discovered that the most effective smiles hit a 'sweet spot' that is not too wide, and which avoids excessive tooth exposure.
The results could be of special interest to Virgin boss Richard Branson, ex-Taoiseach Enda Kenny or Kate Middleton (right), who are all famous for their fulsome toothy grins.
Researchers tested the reactions of some 802 volunteers to a series of computer-generated 3D faces.
Each featured varying kinds of smile.
The expressions were altered by varying the mouth angle, teeth visibility, and the breadth of smiles, as well as their symmetry.
Participants were asked to rate smiles based on their effectiveness, genuineness, pleasantness and also on the perceived emotional intent.
The most "successful" smiles were the ones which achieved an "optimal balance" of teeth, mouth angle and of smile extent.
They also got a more positive response if they developed symmetrically, with the left and right sides matching within 125 milliseconds.
Writing in the journal 'Public Library of Science ONE', Dr Nathaniel Helwig and colleagues from the University of Minnesota concluded that a 'successful smile' is defined as being one that is rated as effective, genuine, and which is 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," Dr Helwig said of the research.
"These findings have broad applications in a variety of areas, such as facial reanimation surgery, rehabilitation, computer graphics and psychology," he added.