Growth and development of the third permanent molar in Paranthropus robustus from Swartkrans, South Africa

Third permanent molars (M3s) are the last tooth to form but have not been used to estimate age at dental maturation in early fossil hominins because direct histological evidence for the timing of their growth has been lacking. We investigated an isolated maxillary M3 (SK 835) from the 1.5 to 1.8-million-year-old (Mya) site of Swartkrans, South Africa, attributed to Paranthropus robustus. Tissue proportions of this specimen were assessed using 3D X-ray micro-tomography. Thin ground sections were used to image daily growth increments in enamel and dentine. Transmitted light microscopy and synchrotron X-ray fluorescence imaging revealed fluctuations in Ca concentration that coincide with daily growth increments. We used regional daily secretion rates and Sr marker-lines to reconstruct tooth growth along the enamel/dentine and then cementum/dentine boundaries. Cumulative growth curves for increasing enamel thickness and tooth height and age-of-attainment estimates for fractional stages of tooth formation differed from those in modern humans. These now provide additional means for assessing late maturation in early hominins. M3 formation took ≥ 7 years in SK 835 and completion of the roots would have occurred between 11 and 14 years of age. Estimated age at dental maturation in this fossil hominin compares well with what is known for living great apes

Molecular to Macroscale Energy Absorption Mechanisms in Biological Body Armour Illuminated by Scanning X-ray Diffraction with In Situ Compression.

Determining multiscale, concurrent strain, and deformation mechanisms in hierarchical biological materials is a crucial engineering goal, to understand structural optimization strategies in Nature. However, experimentally characterizing complex strain and displacement fields within a 3D hierarchical composite, in a multiscale full-field manner, is challenging. Here, we determined the in situ strains at the macro-, meso-, and molecular-levels in stomatopod cuticle simultaneously, by exploiting the anisotropy of the 3D fiber diffraction coupled with sample rotation. The results demonstrate the method, using the mineralized 3D α-chitin fiber networks as strain sensors, can capture submicrometer deformation of a single lamella (mesoscale), can extract strain information on multiple constituents concurrently, and shows that α-chitin fiber networks deform elastically while the surrounding matrix deforms plastically before systematic failure under compression. Further, the results demonstrate a molecular-level prestrain gradient in chitin fibers, resulting from different mineralization degrees in the exo- and endo cuticle

<i>In vivo</i> X-ray elemental imaging of single cell model organisms manipulated by laser-based optical tweezers

We report on a radically new elemental imaging approach for the analysis of biological model organisms and single cells in their natural, in vivo state. The methodology combines optical tweezers (OT) technology for non-contact, laser-based sample manipulation with synchrotron radiation confocal X-ray fluorescence (XRF) microimaging for the first time. The main objective of this work is to establish a new method for in vivo elemental imaging in a two-dimensional (2D) projection mode in free-standing biological microorganisms or single cells, present in their aqueous environment. Using the model organism Scrippsiella trochoidea, a first proof of principle experiment at beamline ID13 of the European Synchrotron Radiation Facility (ESRF) demonstrates the feasibility of the OT XRF methodology, which is applied to study mixture toxicity of Cu-Ni and Cu-Zn as a result of elevated exposure. We expect that the new OT XRF methodology will significantly contribute to the new trend of investigating microorganisms at the cellular level with added in vivo capability

Synchrotron X-ray fluorescence imaging of strontium incorporated into the enamel and dentine of wild-shot orangutan canine teeth

Objectives Dental hard tissues contain trace elements of both dietary and environmental origin. One objective was to demonstrate that a longitudinal record of synchronous Sr incorporation into enamel and dentine can be retrieved from museum specimens of once-free-living endangered species. Further objectives were to quantify sudden fluctuations in Sr concentration and estimate the extent of Sr overprinting back into dentine and enamel formed prior to the time of Sr ingestion. Materials and methods Daily incremental markings were used to determine rates and times of tooth formation and synchrotron X-ray fluorescence of the same polished ground sections to image Sr distribution in a male and a female orangutan canine. The X-ray beam was monochromatised to 17.0 keV and focused to 500 × 500 nm2. Scans were performed at either 25.0 or 5.0 μm resolution. Results Baseline Sr levels ranged between 215-750 ppm. Multiple short, intense Sr labels reaching 750- 1,625 ppm occurred randomly throughout 15-22 years of tooth formation. In dentine, Sr concentration increased gradually away from the EDJ, while in enamel, it reduced towards the enamel surface. Using daily incremental markings, Sr overprinting into earlier formed dentine and enamel was estimated to be ∼12-45 days. There was no evidence of Sr overprinting by maturational ameloblasts. Conclusions A good record of growth and trace element incorporation into tooth tissues can be retrieved from museum specimens. Short, intense Sr labels were equally well time-resolved in enamel and dentine and could be distinguished from more diffuse background levels. Enamel maturation appears to have no quantifiable effect

Synchrotron X-ray fluorescence mapping of Ca, Sr and Zn at the neonatal line in human deciduous teeth reflects changing perinatal physiology

Objectives Our first objective was to review the evidence describing the appearance and microstructure of the neonatal line in human deciduous teeth and to link this with known changes in neonatal physiology occurring at and around birth. A second objective was to explore ways to improve identification of the neonatal line by mapping the pre- and postnatal distribution of Ca, Sr and Zn in deciduous cuspal enamel and superimposing these maps onto transmitted light micrographs that included a clear true section of the neonatal line. Materials and methods We used synchrotron X-ray fluorescence to map elemental distributions in pre- and postnatal enamel and dentine. Two deciduous canines and 5 deciduous molars were scanned with an X-ray beam monochromatised to 17.0 keV at either 10.0, 2.5 or 1.0 μm resolution and 10 ms integration time. Results Calcium maps distinguished enamel and dentine but did not clearly demarcate tissues formed pre- or postnatally. Strontium maps reflected presumed pre- and postnatal maternal serum levels and what are likely to be diet-dependent regions of Sr enrichment or depletion. Prenatal Zn maps, particularly for dentine, mirror elevated levels in the fetus and in colostrum during the first few days of life. Conclusions The neonatal line, enamel dentine junction and surface enamel were all Zn-rich. Within the neonatal line Zn may be associated with increased crystallinity but also with caries resistance, both of which have been reported previously. Elemental mapping may improve the identification of ambiguous NNLs and so be useful in forensic and archaeological studies

Synchrotron X-ray fluorescence imaging of strontium incorporated into the enamel and dentine of wild-shot orangutan canine teeth

Objectives: Dental hard tissues contain trace elements of both dietary and environmental origin. One objective was to demonstrate that a longitudinal record of synchronous Sr incorporation into enamel and dentine can be retrieved from museum specimens of once-free-living endangered species. Further objectives were to quantify sudden fluctuations in Sr concentration and estimate the extent of Sr overprinting back into dentine and enamel formed prior to the time of Sr ingestion.Materials and Methods: Daily incremental markings were used to determine rates and times of tooth formation and synchrotron X-ray fluorescence of the same polished ground sections to image Sr distribution in a male and a female orangutan canine. The X-ray beam was monochromatised to 17.0 keV and focused to 500x500 nm$^2$. Scans were performed at either 25.0 or 5.0 µm resolution.Results: Baseline Sr levels ranged between 215-750 ppm. Multiple short, intense Sr labels reaching 750-1,625 ppm occurred randomly throughout 15-22 years of tooth formation. In dentine, Sr concentration increased gradually away from the EDJ, while in enamel, it reduced towards the enamel surface. Using daily incremental markings, Sr overprinting into earlier formed dentine and enamel was estimated to be ~12-45 days. There was no evidence of Sr overprinting by maturational ameloblasts.Conclusions: A good record of growth and trace element incorporation into tooth tissues can be retrieved from museum specimens. Short, intense Sr labels were equally well time-resolved in enamel and dentine and could be distinguished from more diffuse background levels. Enamel maturation appears to have no quantifiable effect