FACIAL SHAPE IN THE FRANKFURT HORIZONTAL AND NATURAL HEAD POSITION: A METHODOLOGICAL STUDY

Abstract

Introduction. In this article, we have compared frontal facial shapes (based on photo portraits) which were captured in two head positions: Natural position (NP) and Frankfurt horizontal (FH). Materials and methods. In both cases facial shape was analyzed on sex differences and association with direct measurements of body parameters: height, BMI, fat, muscle and bone mass, digit ratio (R2D:4D). The analysis was performed using geometric morphometry methods. The study participants were representatives of the non-European population, Buryats, 86 men and 69 women aged 20 years (20± 2 g). Results. The results showed that (a) head position had a significant impact on the 2D projection of the frontal facial shape, particularly in men; (b) compared to the Natural position, the Frankfurt horizontal position exhibited more pronounced sex differences in facial shape; (c) we observed associations between facial shape and height, BMI, fat, and muscle mass in both men and women in both positions, but these associations were more pronounced in the Frankfurt horizontal. We did not find an association between male facial shape and R2D:4D in the NP position, but we observed it in FH. In women, we did not observe a similar relationship in both positions. Discussion. Our research revealed an important methodological problem: the head position can significantly affect qualitative conclusions about frontal facial shape, especially in non-European populations. In our study, we found a statistical relationship with most body parameters in both cases, FH and NP. However, the relationship was stronger in the FH position. When working with independent parameters that have a generally not very pronounced effect on the facial shape, head position differences can lead to a decrease or even a lack of an association when using a natural position (as in the case of R2D:4D). Conclusion. The obtained results are important for the development of an optimal photography methodology, taking into account the currently accumulated controversial results. Current findings allow us to resolve a number of contradictions related to the zero results observed in modern literature data.