The SPA Factor or Not? Distinguishing Sex on the Basis of Stereotyped Tooth Characteristics

The study examines whether faculty, dental students, or laypeople can determine the sex of a patient solely by looking at the shape of their teeth.

Fifty faculty, 100 students, and 50 patients evaluated 40 photographed smiles for 8,000 observations. The subject group was comprised of 20 males and 20 females. Contingency table analysis was used to determine whether all study participants labeled the smiles similarly and to look for differences within each group. Care was taken to model the effect of individual variation. A nested logistic regression was employed to ascertain differences between faculty, students, and laypeople and to account for the correlation within subjects' responses.

It was expected that 50% of the smiles would be labeled as male and 50% as female. Statistical differences were found for the total group, as all participants were more likely to rate a smile as female (χ2 = 38.19, P < .0001). Using the odds ratio, study participants were 1.32 times more likely to view a smile as female.

Stereotyped "feminine" and "masculine" tooth anatomy characteristics could not predictably be related to the sample smiles either by faculty, students, or public.