Revision for the Journal of Oral Rehabilitation
Manuscript ID: JOR-23-0501
Manuscript title: “What’s in a Smile? The features of Indigenous Fijians’ and NZ Europeans’ smiles”

The study aimed to describe and compare the features of Fijians’ smiles with those of New Zealand Europeans. An observational study was conducted on two ethnic groups, Fijians (FJ; N=23) and New Zealand Europeans (NZ; N=23), age- and gender-matched. All participants were asked to watch amusing videos, and their reactions were video recorded. The videos were analysed by software to assess the frequency, duration, 25 intensity, and genuineness of smiling episodes. Based on the Facial Action Coding System, Action Unit 6 (AU6 - cheek raiser), Action Unit 12 (AU12 - lip corner puller), and Action Unit 25 (AU25 – lips apart) were assessed. Fijians smiled longer than New Zealand Europeans (+19.9%; p=0.027). 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 significantly higher in FJ group than the NZ group.

The study is innovative, really well designed, structured and written. The statistics is appropriate and the reported results are expression of the data found. English grammar and style are appropriate
for the publishing.

The main limitation of the study is that it does not analyze the structural characteristics of the smile at all. Indeed, we could expect that the two ethnic groups may differ in the size of the teeth, chroma, width of the arch, skeletal characteristics of the lower third of the face, morphology of the lips, etc. These and many other factors could be key factors in determining a more or less "friendly" smile. The Authors instead limit the present study to analyzing the dynamic aspects of the smile, in terms of extent, frequency and duration of exposure.

Minor flows:

• On the basis of the previous comment, I would suggest that the authors change the title, as the manuscript analyzes the intensity and frequency of the smile, rather than its intrinsic and structural characteristics.

• Insert better and more detailed description of what Action Unit (AU) 6 (cheek raiser), AU12 (lip corner puller) and AU25 (lips apart) are. It is not clear and easy to understand for the reader.

• Please check the reference section. I.e. Mindess, H. et al and Ekman et al please report pages’ numbers, etc.