title: Biorhythms, deciduous enamel thickness, and primary bone growth: a test of the Havers-Halberg Oscillation hypothesis.
abstract: Across mammalian species, the periodicity with which enamel layers form (Retzius periodicity) in permanent teeth corresponds with average body mass and the pace of life history. According to the Havers-Halberg Oscillation hypothesis (HHO), Retzius periodicity (RP) is a manifestation of a biorhythm that is also expressed in lamellar bone. Potentially, these links provide a basis for investigating aspects of a species' biology from fossilized teeth. Here, we tested intra-specific predictions of this hypothesis on skeletal samples of human juveniles. We measured daily enamel growth increments to calculate RP in deciduous molars (n = 25). Correlations were sought between RP, molar average and relative enamel thickness (AET, RET), and the average amount of primary bone growth (n = 7) in humeri of age-matched juveniles. Results show a previously undescribed relationship between RP and enamel thickness. Reduced major axis regression reveals RP is significantly and positively correlated with AET and RET, and scales isometrically. The direction of the correlation was opposite to HHO predictions as currently understood for human adults. Juveniles with higher RPs and thicker enamel had increased primary bone formation, which suggests a coordinating biorhythm. However, the direction of the correspondence was, again, opposite to predictions. Next, we compared RP from deciduous molars with new data for permanent molars, and with previously published values. The lowermost RP of 4 and 5 days in deciduous enamel extends below the lowermost RP of 6 days in permanent enamel. A lowered range of RP values in deciduous enamel implies that the underlying biorhythm might change with age. Our results develop the intra-specific HHO hypothesis.
authors.affiliation: Human Osteology Lab, Skeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury, UK.
authors.forename: Patrick
authors.initials: P
authors.lastname: Mahoney
authors.affiliation: Department of Medicine, Imperial College London, London, UK.
authors.forename: Justyna J
authors.initials: JJ
authors.lastname: Miszkiewicz
authors.affiliation: Human Osteology Lab, Skeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury, UK.
authors.forename: Rosie
authors.initials: R
authors.lastname: Pitfield
authors.affiliation: Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Schlecht
authors.affiliation: Human Osteology Lab, Skeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury, UK.
authors.forename: Chris
authors.initials: C
authors.lastname: Deter
authors.affiliation: Department of Anthropology, The Ohio State University, Columbus, OH, USA.
authors.forename: Debbie
authors.initials: D
authors.lastname: Guatelli-Steinberg
mesh_terms: D001846:Bone Development; D003743:Dental Enamel / Q000502:physiology*; D006801:Humans; D008963:Molar / Q000502:physiology; D010507:Periodicity; D014094:Tooth, Deciduous / Q000502:physiology*
keywords: Retzius lines; enamel thickness; microstructure; primary osteons