Craniofacial growth, maturation, and change: teens to midadulthood

Despite the attainment of several adult cranial dimensions relatively early in childhood, skeletal maturity and, by consequence, adult form are typically defined by the eruption of the third molars around 17 years of age. This in turn serves as the division between subadults and adults, which is then applied to population studies of biological variation. Specifically, comparative data sets of adult measurements are not directly applied to individuals who do not have complete skeletal growth, as it is believed that the confounding effects of allometry may skew the results. The present study uses geometric morphometrics techniques to investigate the appropriateness of this division with respect to three-dimensional anatomical landmarks. Twenty-six landmarks were collected from a single population of 24 crania partitioned into 4 age groups spanning late adolescence to midadulthood. Generalized Procrustes and multivariate statistical analyses were performed on the landmark data. Results showed no significant morphological differences between the teen and young adult age groups, whereas significant shape and size differences were found in older adults relative to their younger cohorts. Moreover, no growth-related shape variation (ie, allometry) was detected within the sample. These findings suggest that adult form is attained several years earlier than commonly thought and corroborate other research that suggest that subtle changes in cranial morphology continue throughout adulthood.