Thick enamel, thin bone: a common link in human juvenile hard tissue growth?

The Havers-Halberg oscillation hypothesis (HHO) proposes that an underlying biorhythm may have a role in hard tissue growth, in relation to body size and life history, when compared between some mammalian species. Recent studies explored this hypothesis within adult humans, revealing attained stature and final permanent molar enamel thickness related to the biorhythm. This study searches for evidence of a link between cortical bone width and enamel thickness, in a sample of human juvenile skeletons (n=45) aged between three to 13 years of age. Histological thin sections were removed from the anterior mid-shaft region of the humerus, and from the permanent first maxillary molar of each skeleton. Cortical width and 2D average enamel thickness were measured from thin sections using Cell Sens image analysis software. Analyses revealed a significant and negative correlation (p=0.008) between enamel thickness and cortical width when the sample was subdivided into age groups. Thus, children with thicker molar enamel generally had thinner cortical bone, though this correlation was much stronger in the older children. These preliminary findings demonstrate a potential age-related link between enamel and bone growth in human children. Ongoing PhD research will examine these measures of enamel and bone thickness against evidence of a biorhythm retained in tooth enamel, and the underlying cellular mechanisms responsible for the morphology of hard tissue in these children.