A Neanderthal from the Central Western Zagros, Iran. Structural reassessment of the Wezmeh 1 maxillary premolar.

Wezmeh Cave, in the Kermanshah region of Central Western Zagros, Iran, produced a Late Pleistocene faunal assemblage rich in carnivorans along with a human right maxillary premolar, Wezmeh 1, an unerupted tooth from an 8 ± 2 year-old individual. Uranium-series analyses of the fauna by alpha spectrometry provided age estimates between 70 and 11 ka. Crown dimensions place the tooth specimen at the upper limits of Late Pleistocene human ranges of variation. Wezmeh 1 metameric position (most likely a P3) remains uncertain and only its surficial morphology has been described so far. Accordingly, we used microfocus X-ray tomography (12.5 µm isotropic voxel size) to reassess the metameric position and taxonomic attribution of this specimen. We investigated its endostructural features and quantified crown tissue proportions. Topographic maps of enamel thickness (ET) distribution were also generated, and semilandmark-based geometric morphometric analyses of the enamel-dentine junction (EDJ) were performed. We compared Wezmeh 1 with unworn/slightly-moderately worn P3 and P4 of European Neanderthals, Middle Paleolithic modern humans from Qafzeh, an Upper Paleolithic premolar, and Holocene humans. The results confirm that Wezmeh 1 represents a P3. Based on its internal conformation and especially EDJ shape, Wezmeh 1 aligns closely with Neanderthals and is distinct from the fossil and extant modern human pattern of our comparative samples. Wezmeh 1 is thus the first direct evidence of Neanderthal presence on the western margin of the Iranian Plateau.

The biorhythm of human skeletal growth.

Evidence of a periodic biorhythm is retained in tooth enamel in the form of Retzius lines. The periodicity of Retzius lines (RP) correlates with body mass and the scheduling of life history events when compared between some mammalian species. The correlation has led to the development of the inter-specific Havers-Halberg oscillation (HHO) hypothesis, which holds great potential for studying aspects of a fossil species biology from teeth. Yet, our understanding of if, or how, the HHO relates to human skeletal growth is limited. The goal here is to explore associations between the biorhythm and two hard tissues that form at different times during human ontogeny, within the context of the HHO. First, we investigate the relationship of RP to permanent molar enamel thickness and the underlying daily rate that ameloblasts secrete enamel during childhood. Following this, we develop preliminary research conducted on small samples of adult human bone by testing associations between RP, adult femoral length (as a proxy for attained adult stature) and cortical osteocyte lacunae density (as a proxy for the rate of osteocyte proliferation). Results reveal RP is positively correlated with enamel thickness, negatively correlated with femoral length, but weakly associated with the rate of enamel secretion and osteocyte proliferation. These new data imply that a slower biorhythm predicts thicker enamel for children but shorter stature for adults. Our results develop the intra-specific HHO hypothesis suggesting that there is a common underlying systemic biorhythm that has a role in the final products of human enamel and bone growth.

Brief communication: Comparative patterns of enamel thickness topography and oblique molar wear in two Early Neolithic and medieval population samples.

Enamel thickness has been linked to functional aspects of masticatory biomechanics and has been demonstrated to be an evolutionary plastic trait, selectively responsive to dietary changes, wear and tooth fracture. European Late Paleolithic and Mesolithic hunter-gatherers mainly show a flat wear pattern, while oblique molar wear has been reported as characteristic of Neolithic agriculturalists. We investigate the relationships between enamel thickness distribution and molar wear pattern in two Neolithic and medieval populations. Under the assumption that dietary and/or non-dietary constraints result in directional selective pressure leading to variations in enamel thickness, we test the hypothesis that these two populations will exhibit significant differences in wear and enamel thickness patterns. Occlusal wear patterns were scored in upper permanent second molars (UM2) of 64 Neolithic and 311 medieval subadult and adult individuals. Enamel thickness was evaluated by microtomography in subsamples of 17 Neolithic and 25 medieval individuals. Eight variables describing enamel thickness were assessed. The results show that oblique molar wear is dominant in the Neolithic sample (87%), while oblique wear affects only a minority (42%) of the medieval sample. Moreover, in the Neolithic molars, where buccolingually directed oblique wear is dominant and greatest enamel lost occurs in the distolingual quadrant, thickest enamel is found where occlusal stresses are the most important-on the distolingual cusp. These results reveal a correlation between molar wear pattern and enamel thickness that has been associated to dietary changes. In particular, relatively thicker molar enamel may have evolved as a plastic response to resist wear.

How well do parents identify their child's baby teeth? Engagement and accuracy of parent-reported information on a tooth checklist survey.

OBJECTIVES: Naturally exfoliated primary teeth are being increasingly collected in child development studies. Most of these odontological collections and tooth biobanks use parent-reported information from questionnaires or tooth checklists to collect data on offspring teeth. To the best of the authors' knowledge, no studies have assessed parental engagement in tooth checklists, nor parental accuracy in identifying their child's baby tooth. This study aimed to evaluate these dimensions by analysing data from the about this tooth checklist returned with donated primary teeth in a natural experimental study called STRONG (the Stories Teeth Record of Newborn Growth). METHODS: Parental self-reported information were analysed on checklists returned with 825 primary teeth belonging to 199 children. The percentage of blank answers was calculated for each question. The accuracy of parents-reported tooth identification was evaluated by comparing parental ratings to researchers' ratings. Reliability of researchers' tooth identification was first evaluated by calculating intra-observer and inter-observer agreements, as well as Cohen's Kappa values. The percentage of accuracy of parents' tooth identification (relative to researcher's) was then calculated, and logistic regressions were used to evaluate if time elapsed between when exfoliation occurred and the checklist was completed associated with parental accuracy in tooth identification. RESULTS: Parents returned 98.4% of the checklists and completed 74.9% to 97.7% of the questions. Excellent reliability was demonstrated for researchers' intra- and inter-rater tooth identification (agreement percentages >90%; Cohen's Kappa values >.83). Moderate accuracy of parents-reported tooth identifications was found, with parents correctly identifying 49.5% of the donated tooth. Better parental accuracies were highlighted for partial identifications (87.1% of correct jaw, 75.6% of correct tooth type, and 65.8% of correct lateralization). Logistic regressions showed the odds of correct parental identifications decreased on average by 1.8% every 30 days of distance between tooth exfoliation and checklist completion. CONCLUSIONS: While parental engagement is high, parents-reported tooth identifications have moderate accuracy, which decreases over time. High accuracy is however found for partial identifications. Parent-reported information on the accompanying questionnaire of naturally exfoliated primary teeth collection or tooth biobanks, even when filled in a long time after exfoliation took place, should be encouraged. However, expert identifications of teeth should remain best practice.

Evaluation of age, sex, and ancestry-related variation in cortical bone and dentine volumes in modern humans, and a preliminary assessment of cortical bone-dentine covariation in later Homo.

Cortical bone and dentine share similarities in their embryological origin, development, and genetic background. Few analyses have combined the study of cortical bone and dentine to quantify their covariation relative to endogenous and exogenous factors. However, knowing how these tissues relate in individuals is of great importance to decipher the factors acting on their evolution, and ultimately to understand the mechanisms responsible for the different patterns of tissue proportions shown in hominins. The aims of this study are to examine age-, sex-, and ancestry-related variation in cortical bone and dentine volumes, and to preliminary assess the possible covariation between these tissues in modern humans and in five composite Neandertals. The modern analytical sample includes 12 immature individuals from France and 49 adults from France and South Africa. Three-dimensional tissue proportions were assessed from microtomographic records of radii and permanent maxillary canines. Results suggest ontogenic differences and a strong sexual dimorphism in cortical bone and dentine developments. The developmental pattern of dentine also seems to vary according to individual's ancestry. We measure a stronger covariation signal between cortical bone and dentine volumes than with any other dental tissue. A more complex covariation pattern is shown when splitting the modern sample by age, sex, and ancestry, as no signal is found in some subsamples while others show a covariation between cortical bone and either crown or radicular dentine. Finally, no difference in cortical bone volume is noticed between the modern young adults and the five young adult composite Neandertals from Marine Isotopic Stages (MIS) 5 and 3. Greater dentine Cortical bone and dentine (co)variation volumes are measured in the MIS 5 chimeric Neandertals whereas a strong interpopulation variation in dentine thickness is noticed in the MIS 3 chimeric Neandertals. Further research on the cortical bonedentine covariation will increase understanding of the impact of endogenous and exogenous factors on the development of the mineralized tissues.

The Tooth Fairy collection (la collection Petite souris), a sample of documented human deciduous teeth at the University of Bordeaux, France.

The aim of this article is to describe the composition of the Tooth Fairy collection (collection Petite souris as it is known in French), a documented sample of deciduous teeth from individuals with known kinship curated at the University of Bordeaux (France). Since 2014, we have collected naturally exfoliated deciduous teeth from French children of known kinship and life histories. The life-history records include date and place of birth, sex, birth weight, and length, weight measurements during the first 6 months of life, whether the child was born premature or full-term, delivery conditions, and dietary information including weaning age. Data collection and exploitation was approved by the French authority Commission Nationale de l'Informatique et des Libertés. The collection, which is still expanding, is currently composed of 995 deciduous teeth belonging to 99 individuals from 42 families. The sample includes 61 female individuals and 38 male individuals, born between 1953 and 2013, the majority from France. Siblings are the most represented kinship type within the collection. The Tooth Fairy collection of deciduous teeth from individuals with known life history and kinship offers a unique window into the variation in human growth. Available for macro-, meso-, and microstructural analysis, the collection offers new insights into the multiple factors influencing dental growth, human variation, and diet, especially around birth and during early postnatal life. This collection is particularly relevant for studies in forensic, dental, and biological anthropology.

Enamel daily secretion rates of deciduous molars from a global sample of children.

OBJECTIVE: To investigate and describe the variation in enamel daily secretion rates (DSRs) of naturally exfoliated deciduous molars (n = 345) from five modern-day populations (Aotearoa New Zealand, Britain, Canada, France, and Sweden). DESIGN: Each tooth was thin sectioned and examined using a high-powered Olympus BX51 microscope and DP25 digital microscope camera. Mean DSRs were recorded for the inner, mid, and outer regions of cuspal and lateral enamel, excluding enamel nearest the enamel-dentin junction and at the outermost crown surface. RESULTS: Mean DSRs did not vary significantly between populations, or by sex. Cuspal enamel grew slightly faster than lateral enamel (mean difference 0.16 µm per day; p < 0.001). The trajectory of DSRs remained relatively constant from inner to outer cuspal enamel and increased slightly in lateral enamel (p = 0.003). CONCLUSIONS: The DSRs of deciduous molars from modern-day children are remarkably consistent when compared among populations. While growth rates are faster in cuspal than lateral enamel, the trajectory of enamel formation changes only slightly from inner to outer regions. The trajectory of DSRs for deciduous molars differs to that of permanent molar enamel, which typically display a steep increase in matrix deposition from inner to outer enamel.

Internal Tooth Structure and Burial Practices: Insights into the Neolithic Necropolis of Gurgy (France, 5100-4000 cal. BC).

Variations in the dental crown form are widely studied to interpret evolutionary changes in primates as well as to assess affinities among human archeological populations. Compared to external metrics of dental crown size and shape, variables including the internal structures such as enamel thickness, tissue proportions, and the three-dimensional shape of enamel-dentin junction (EDJ), have been described as powerful measurements to study taxonomy, phylogenetic relationships, dietary, and/or developmental patterns. In addition to providing good estimate of phenotypic distances within/across archeological samples, these internal tooth variables may help to understand phylogenetic, functional, and developmental underlying causes of variation. In this study, a high resolution microtomographic-based record of upper permanent second molars from 20 Neolithic individuals of the necropolis of Gurgy (France) was applied to evaluate the intrasite phenotypic variation in crown tissue proportions, thickness and distribution of enamel, and EDJ shape. The study aims to compare interindividual dental variations with burial practices and chronocultural parameters, and suggest underlying causes of these dental variations. From the non-invasive characterization of internal tooth structure, differences have been found between individuals buried in pits with alcove and those buried in pits with container and pits with wattling. Additionally, individuals from early and recent phases of the necropolis have been distinguished from those of the principal phase from their crown tissue proportions and EDJ shape. The results suggest that the internal tooth structure may be a reliable proxy to track groups sharing similar chronocultural and burial practices. In particular, from the EDJ shape analysis, individuals buried in an alcove shared a reduction of the distolingual dentin horn tip (corresponding to the hypocone). Environmental, developmental and/or functional underlying causes might be suggested for the origin of phenotypic differences shared by these individuals buried in alcoves.