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Scientists have identified the specific features of a person’s face, lips, and teeth that are more likely to make one’s smile be perceived as attractive, an advance that could lead to better dental and cosmetic treatment planning.
Smiling is a universal human expression of happiness, but its facial characteristics vary across ethnic groups.
Researchers have identified several smile characteristics, including the smile line, smile arc, upper lip curvature, and symmetry.
But these previous studies on the facial features of smiling have mostly focused on Caucasian populations, researchers say.
Now, scientists have taken a systematic look at the problem, recording and analysing the dynamic smiles of nearly 500 young Vietnamese adults with an average age of 21.
Researchers recorded dynamic smiles of the participants, capturing the full motion of their lips, teeth, and surrounding soft tissues as they smiled.
This approach was important, according to scientists, as a smile is not a fixed structure, but a movement.
The way tissues travel during a smile can change which teeth are visible, how the lips curve, and how much of the gingiva and buccal corridor is exposed, they say,
Each participant was recorded twice – once with their lips at rest and another while producing a natural, unforced smile.
The images were also standardised for brightness, contrast, size and head position.
Scientists sought to determine which facial and oral parameters shape how a smile looks, and how attractive it is perceived to be.
They examined eight characteristics of smiles and nine additional facial or oral measurements, including upper lip curvature, smile arc, smile symmetry, and tooth display.
One parameter researchers specifically looked at was the anterior smile line, an imaginary curved line that follows the bottom edges of your upper front teeth when one smiles.
They also looked at each participant’s buccal corridor space, the triangular region between the corners of the mouth and the outer surfaces of the upper back teeth.
The smile index, calculated as the ratio of smile width to smile height, was also measured for each participant.
Researchers also matched these measures with others like upper lip length, lip mobility, and mouth size.
Participants were then classified according to how attractive their smiles were judged to be.
Three of the facial features – the anterior smile line, the smile arc, and upper lip curvature – showed broad associations with several smile assessments.
A person’s smile symmetry, a feature that many patients and clinicians intuitively value, is significantly linked to upper lip length during smiling, researchers found.
Scientists could identify the specific soft tissue and dental factors contributing to the attractiveness of a person’s smile.
These kinds of predictive relationships are valuable to orthodontists and surgeons.
The findings support the clinical intuition that altering a person’s tooth position can meaningfully change the overall character of a smile as these elements intertwined.
“This study provides a comprehensive dataset on smile morphology, facial and oral factors,” researchers wrote.
The research, according to scientists offer the most detailed portraits of smile morphology in a Southeast Asian population to date and can inform future “individualised aesthetic treatment planning”.