How much teeth should you show when you smile? How wide should your grin be, and what if it's crooked? Using a variety of computer-animated faces, researchers from the University of Minnesota have done their best to isolate the traits of a winning smile.
At first glance, this may seem like a laughing matter. But for people with paralysis or other medical conditions, being physically unable to smile can cause communication problems, anxiety, and depression. The new study, published today in PLOS One, could help doctors who perform facial reanimation surgery and rehabilitation—understanding the characteristics of a great smile will help to make sure a grin doesn't look like a grimace.
To start, the researchers had an artist create 27 different smiles on a computer-animated face. The smile's angle, width, toothiness, and degree of crookedness varied across each face. Then the authors asked 802 people at the Minnesota State Fair to rate each one based on its effectiveness (Very Bad to Very Good), genuineness (Fake vs Genuine), pleasantness (Creepy to Pleasant), and the emotion expressed (Anger, Contempt, Disgust, Fear, Happiness, Sadness, or Surprise).
Related: Best celebrity smiles:
By and large, they found that less is more when it comes to a successful smile. HOWEVER. It's worth noting that the width of the model's eyes never changed, even when his smile was bigger, so it's no wonder the test subjects hated the look of such a wide grin.
Ordinarily, a big smile makes your eyes crinkle at the corners, but the study authors left their model's eyes alone because facial reconstruction techniques are pretty limited when it comes to restoring movement around the eyes. Bottom line: If you have full control of your facial muscles, chances are your giant grin is still charming AF.
In the chart below, the best-rated smiles are shown in green, whereas the less pleasant ones are red. It turns out there are a variety of combinations that make for a nice smile. "[T]here is not a single path to a successful smile," the paper notes. Nevertheless, here are a few of the takeaways.
These 27 faces differ slightly in their width ("extent"), flatness ("angle"), and toothiness ("dental show"). Faces that received a higher rating have a green background, while the ones in red received low ratings. Each face was judged on its effectiveness, genuineness, and pleasantness—these three different ratings make up three color bars behind each image.
Helwig et al 2017
Related: Famous dimples
Bigger is not always better
Reconstructive surgeons tend to think that bigger is better. But that's not quite right. In this study, smiles with a low to medium width ("extent") tended to get better ratings. Big smiles were rated worst when combined with a high angle (or upturn) and a lot of teeth.
Not too sharp
Smiles with a medium angle or upturn tended to be more popular, while the more V-shaped smiles creeped people out.
Cut your teeth
Apparently, medical professionals are divided on how important it is to show your teeth when you're smiling. This study found that open-mouth smiles can easily be mistaken for a sign of fear or contempt—the two lowest rated smiles were both pretty toothy. Better to go with no teeth, or just show your chompers off a little.
A little asymmetry can be a good thing
The researchers also played around with the timing and asymmetry of each smile, and they found that a slight crookedness is actually better than none—it probably makes people feel like the smile is more genuine. But if the left and right sides of the mouth weren't synced within 125 milliseconds, people started to get weirded out.
Slightly crooked smiles can be pleasant, but extremely crooked smiles just seem creepy.
Helwig et al 2017
These sorts of studies can help in psychology and computer graphics, in addition to facial reanimation. The researchers hope that future studies will look at more variables—including eye crinkles—to paint an even more accurate picture of the perfect smile.