What’s in a Smile? An investigation of the effect of ethnic background on smiling features

Abstract

Objectives: The Fijian smile, also called the “Bula Smile,” is often described as the world’s friendliest. The description of Bula Smile, however, remains anecdotal. This project aimed to describe and compare the features of Fijians’ smiles with those of New Zealand Europeans.

Methods: An observational study was conducted on two ethnic groups, Fijians (FJ; N=23) and New Zealand Europeans (NZ; N=23), matched for age and gender. All participants were asked to watch a series of amusing videos, and their reactions were recorded using a 4K web camera. The videos were analysed using bespoke pattern recognition software to assess the frequency, duration, intensity, and genuineness of smiling episodes. The software had been previously validated against the Facial Action Coding Systems (FACS) Action Units 6 (AU6 - cheek raiser), 12 (AU12 - lip corner puller), and 25 (AU25 – lips apart) (see Chapter 2 for details). The participants also completed a 60-item personality (IPIP NEO) and the Smile Esthetics-Related Quality of Life measures (SERQoL). Malocclusions were assessed using the Dental Aesthetic Index (DAI). Data were analysed by generalised linear models.

Results: Fijians smiled longer than New Zealand Europeans (+19.9%; p=0.027), but the number of smiles per minute did not differ between groups (p=0.083). Mean intensity of AU6 (+1.0; 95%CIs=0.6-1.5; p<0.001), AU12 (+0.5; 95%CIs=0.1-0.9; p=0.008) and AU25 (+22.3%; 95%CIs=7.3-37.3%; p=0.005) were all significantly higher in FJ group than in NZ group. Compared to the NZ group, the FJ group scored lower on openness (-4.0; P=0.026) and higher on SERQoL (+3.0; P=0.003), the latter indicating less confidence with their smile. The DAI index did not differ between the two ethnic groups.

Conclusion: Smiling features of Fijians and New Zealanders showed objective differences, as represented by the mean activity of FACS AUs, which could not be explained by personality traits, self-confidence with their smile, and malocclusion severity. The most distinctive trait of the Fijians smile was the higher activation of the Duchenne’s marker (AU6), which indicates “smiling with the eyes”, and is regarded as a sign of smile genuineness.