Modelling 3D craniofacial growth trajectories for population comparison and classification illustrated using sex-differences

Abstract

Many disorders present with characteristic abnormalities of the craniofacial complex. Precise descriptions of how and when these abnormalities emerge and change during childhood and adolescence can inform our understanding of their underlying pathology and facilitate diagnosis from craniofacial shape. In this paper we develop a framework for analysing how anatomical differences between populations emerge and change over time, and for binary group classification that adapts to the age of each participant. As a proxy for a disease-control comparison we use a database of 3D photographs of normally developing boys and girls to examine emerging sex-differences. Essentially we define 3D craniofacial ‘growth curves’ for each sex. Differences in the forehead, upper lip, chin and nose emerge primarily from different growth rates between the groups, whereas differences in the buccal region involve different growth directions. Differences in the forehead, buccal region and chin are evident before puberty, challenging the view that sex differences result from pubertal hormone levels. Classification accuracy was best for older children. This paper represents a significant methodological advance for the study of facial differences between growing populations and comprehensively describes developing craniofacial sex differences.

Quantification of mandibular sexual dimorphism during adolescence

“…We also applied a flexible, non‐linear modelling technique that does not assume any particular form of the growth trajectory (Matthews et al. ). To the best of our knowledge, only Coquerelle et al.…”

“…() and Matthews et al. (). The goal is to estimate the expected shape or form of the mandible at each age as well as the expected rate and direction of change at each point on the mandible.…”

“…Using a large cross‐sectional database of pre‐orthodontic treatment CBCT images, we modelled the growth trajectories of human mandibles in males and females separately, using a recently developed non‐linear modelling framework (Matthews et al. ). We examined the rate and direction of change within each group and compared the growth trajectories to examine how sexual dimorphism in the mandible develops during adolescence.…”

SNPs Associated With Testosterone Levels Influence Human Facial Morphology

“…The impact of sex hormones on human craniofacial morphology is well documented and is most apparent in the post-pubertal dimorphism we see between male and female faces ( Kesterke et al, 2016 ; Matthews et al, 2018 ). The most prominent sex differences in human facial morphology tend to involve the mandible, zygomatic region (cheeks), lips, forehead, and nose ( Toma et al, 2008 ; Koudelová et al, 2015 ; Kesterke et al, 2016 ; Matthews et al, 2018 ).…”

“…Differences in facial morphology between males and females are well documented, with major shape differences apparent in the jaw, lips, eyes, nose and cheek regions ( Toma et al, 2008 ; Klotz et al, 2010 ; Claes et al, 2012b ; Koudelová et al, 2015 ). Although facial sexual dimorphism has now been described in children ( Kesterke et al, 2016 ; Matthews et al, 2016 , 2018 ), differences become much more pronounced after the onset of puberty. This accelerated dimorphism post-puberty is the result of changes in circulating hormone levels, which regulate the development and differentiation of male and female primary and secondary sex characteristics, such as voice, body shape and facial morphology ( Hines, 2011 ).…”