The Big Book of British Smiles

With apologies to readers the United Kingdom and Ireland, the title of this post refers to an infamous scene from the long-running American animated comedy series The Simpsons.  In in the examination room of “Painless Dentistry” (“formerly ‘Painful Dentistry'”), a particularly stern dentist chastises his young patient for failing to brush his teeth.  To coerce the young offender to adopt better oral hygiene practices, the dentist brings out his Big Book of British Smiles and commences to flip through its pages.  The young boy is horrified as snaggletoothed grin after snaggletoothed grin greet him.  His spirit finally breaks when he sees one too many British smiles (including one face that bears a striking resemblance to the Prince of Wales), and he begins to weep, presumably now thoroughly frightened into adopting good brushing and flossing habits.

Hilarious coercion and undeserved stereotypes aside, the point of The Big Book of British Smiles is obvious: take care of your teeth, or you’ll look ugly.  Which begs the question: why do we want our teeth to look nice?  In the United States alone, we spend over $1 billion each year on cosmetic dental procedures, from teeth whitening to orthodontics.  But why?  Is this just a cultural value, a product of our improved hygiene and modern dental practices?  Or, could this obsession with a straight set of pearly whites have a more ancient origin?

Biologists and psychologists have previously suggested our fixation with good teeth serves a very practical, necessary, and ancient purpose.  Beyond their primary biological roles in chewing and tearing food, we put our teeth on display a lot, and use them to infer the state of each other’s health, well-being, and habits.  We show our teeth off when we smile, laugh, and talk.  Tooth appearance and arrangement convey accurate information about an individual’s genetic instructions, general health, disease susceptibility, diet, hygiene, and life history.  The general trends are obvious: tooth loss and odd tooth shape or spacing can indicate poor diet, genetic disorders, or traumatic life events.  Teeth can discolor as tooth enamel thins with age or from diet, nutritional deficiencies, or genetic predisposition.  Given the prominence of our teeth and how often they are put on display, psychologists have wondered if we naturally use display our teeth to show robust health and diet, or to communicate other positive features about ourselves, particularly to potential mates.  If we do, then how do others (including potential mates) perceive these signals?  What specific features of tooth arrangement or color communicate different ideas about health and attractiveness?

New research published last month in the journal PLoS One has started to address some of these complex questions.  In a study conducted at the University of Leeds, psychologists Colin Hendrie and Gayle Brewer asked two types of questions:

  1. What impact do variations in tooth arrangement and color have on the general attractiveness of men and women?
  2. Do men and women judge these variations in tooth arrangement and color differently for their own sex?  The opposite sex?

To address these questions, Dr. Hendrie took separate photographs of a smiling young man and a smiling young woman.  He digitally altered the teeth in these photographs, replacing healthy toothsome grins with gapped or chipped tooth arrangements, yellowed teeth, or a combinations of these features.  He then showed these altered photographs, as well as the original images, to 75 women and 75 men, and asked his subjects to rate the “attractiveness” of both the man and the woman in the photographs on a simple numeric scale (with higher numbers indicating a more attractive model).  Drs. Hendrie and Brewer dissected the results by tooth feature to identify which alterations in dentition (color vs. arrangement) would most impact the score for both the male and female models.  They also considered the sex of the viewer when analyzing their results, to see if there was a difference in how male or female viewers judged the attractiveness the male and female models, in both the original and altered photographs. 

The original images (left) and examples of altered images (right) with discolored, gapped, or crooked tooth arrangements.

Regarding the results, let’s start with the obvious: giving otherwise lovely models gapped, crooked, or yellow teeth significantly decreased the model’s “attractiveness” rating, regardless of whether that models is a man or a woman.  The effect was most dramatic for yellow or gapped teeth.  Artificially whitening the tooth color in the photographs (from a natural ivory tone to a true white) also made little difference in the “attractiveness” rating of models, regardless of whether the teeth were straight, crooked, or contained gaps.

Hendrie and Brewer also reported a difference in how their viewers rated the male and female models.  For the male model, viewers generally rated the grin with wide gaps as less attractive than naturally-spaced teeth.  Male viewers in particular also didn’t enjoy seeing the male model with yellow teeth in one particular tooth arrangement.  In contrast, the “attractiveness” scores for the female model were much more sensitive to the state of tooth discoloration and arrangement.  For both male and female viewers, most deviations from natural tooth color or a straight tooth arrangement in the female model had a substantially negative impact on how the viewers rated her “attractiveness.”  Thus, while male and female viewers were willing to tolerate more tooth discoloration or gaps and crooked patterning when judging the attraction of the male model, they were not as generous with the female model.

Why would both male and female viewers drop their “attractiveness” scores for the female model so dramatically compared to her male counterpart?  Drs. Hendrie and Brewer hypothesize that, for women, tooth coloration and arrangement are more than just a proxy for overall health, life history, and genetic makeup.  For women, dentition is also a sign of age.  Teeth turn yellow or brown and move out of “ideal” alignment with age, and a straight and healthy-colored grin may be a quick and easy way for a young woman to say, “Yes, I’m healthy and young enough to have children.”  If this theory is true, then a healthy grin may have a “residual reproductive value” for women (to quote Hendrie and Brewer directly); and this signal could be picked up by both male and female viewers, though the consequences are most important for males (since they would be potential males).  In contrast, the relaxed judgment of the study’s viewers toward the male models may reflect the simple biological fact that most men are able to become parents well into middle age (and beyond, thanks to modern medicine), reducing the pressure to flash an age-appropriate grin as a sign of their reproductive potential.

Hot or not?

Hendrie and Brewer’s hypotheses are intriguing, but they certainly have not been tested thoroughly in this study.  By their own admission, Hendrie and Brewer used just one male and and one female model, and both that were relatively young (20-22 years old) and Caucasian.  Thus, even their experimental design has its draw-backs, limiting a broader interpretation of their results.  This study alone cannot address how and why viewers judged the models by their toothy grins.  The best we can conclude for now is that viewers most certainly do judge, and the judgment is more decisive and consequential for the female model.  They are intriguing, and surprising, results, and hopefully a sign that further experiments are in the works!

For now, keep this point in mind: brush and floss twice daily, and see your dentist twice a year.  You shouldn’t need a visit to “Painless Dentistry” to teach you that you’re conveying a lot of information with your smile.



About James Urton

I went to school to become a molecular biologist.  At some point in this long education, I discovered that I love communicating science to the general public: talks, writing, at a pub, on the street corner...  Whatever venue will let me hold your attention for a few moments.  Unfortunately, I can't do this for a living, since no one will pay me.  So, I have a job as a molecular biologist at the University of Washington, where I get to work with great scientists on some really awesome projects, and I'll blog about science here at Muller's Ratchet in my spare time. Why should the general public want to know anything about science? Here's my explanation (which also explains why I chose the name Muller's Ratchet for this site). Briefly as a graduate student (before I had to devote all of my time to graduating), I blogged at Adaptive Radiation.
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