Faculty Bibliography

Despite their importance for understanding the evolutionary foundations of modern human senescence, available data on aging processes in nonhuman primates from well-studied natural environments are rare, with notable exceptions. We examined patterns of skeletal aging in Virunga mountain gorillas from Volcanoes National Park, Rwanda. Virunga gorillas are distinctive in their herbivory, increased terrestriality, and accelerated life history compared to other great apes. Data were collected from naturally accumulated skeletons [N=50 M, 39 F, 5 Unk], including 53 known-age individuals (0-43 years). Virunga gorillas do not show the dental senescence reported in some other primates. While molar percent dentine exposure significantly increases with age, and occlusal topography metrics significantly decrease with age, 3D relative shearing crest length is maintained, even in heavily worn teeth. Periodontal disease, evidenced by alveolar bone loss, increases significantly with age in molars but not premolars. Degenerative bone changes are also common. Degenerative joint disease (eburnation, osteophytes, porosity) significantly increases with age for all joints (forelimb, hindlimb, vertebrae). However, the strength of correlations differs across body compartments and sexes. Long bone diaphyses show medullary expansion and cortical thinning with age, and periosteal expansion that preserves bone strength despite endosteal bone loss. Fore-tohindlimb strength decreases with age in Virunga gorilla females, possibly associated with behavioral changes, but they lack the rapid bone loss characteristic of post-menopausal human females. Skeletal aging processes in Virunga gorillas and other primates may be influenced by local ecology and behavior, and provide insights into the unique features of human aging

The aim of this study was to determine the effects of 38% silver diamine fluoride (SDF) on carious lesions of human deciduous teeth. Ten extracted deciduous incisors with caries were collected and treated with SDF. After the treatment, the teeth were sectioned through the center of the carious lesion. The extent of sliver precipitation was examined using quantitative backscattered electron scanning electron microscopy (qBSE-SEM), energy-dispersive X-ray spectroscopy (EDX), and micro-computed tomography (micro-CT). The qBSE-SEM images revealed that the silver particles could penetrate through the pellicle complex, along with the rod sheaths into the demineralized enamel rods and the dentinal tubules, and form silver-enriched barriers surrounding the carious lesions at depths up to 2,490.2 μm (mean 744.7 ± 448.7 μm) within the dentinal tubules of the carious lesions, but less likely in the sound enamel. The EDX spectrum analysis revealed that carbon, oxygen, phosphorus, chlorine, silver, and calcium were the main elements detected in the lesions treated with SDF. Additionally, sodium, magnesium, aluminum, silicon, zinc, sulfur, and fluorine were detected as the minor elements within the SDF precipitation "zone." The micro-CT analysis further showed that in the deep cavitated lesions, the silver precipitation could be observed in the pulp chamber. These findings provide new evidence defining the SDF mode of action for arresting caries and suggest that the application of a highly concentrated SDF solution on deciduous teeth should be used with caution for various carious lesions.

BACKGROUND:As silver diamine fluoride (SDF) gains popularity for caries arrest, the authors aimed to investigate the content of fluoride and silver in 38% SDF produced for the US market and its short-term stability. METHODS:Five samples of 38% SDF were evaluated when the bottle was first opened, and at 7 and 28 days. Fluoride concentrations were determined with a fluoride ion-selective electrode, and silver concentrations were determined with a simultaneous inductively coupled plasma mass spectrometer. pH was measured with a pH probe. Weight and volume of individual drops were measured. RESULTS:At day 0, 40% of individual measured values were above the expected fluoride concentration, and at day 28, 93% were above the expected fluoride concentration (P = .005). At day 0, 19% of individual measured values were below the lowest expected silver concentration, and at day 28, 93% were below (P < .001). Acidity (pH 10) was consistent over the 3 periods. Mean (standard deviation) weight of a drop was 40 (4.0) milligrams, and mean (standard deviation) volume was 32.55 (1.89) microliters, 30% more than the reported value of 25 μL. CONCLUSION/CONCLUSIONS:Over 28 days, the product pH is stable, whereas the fluoride content tends to increase and the silver content tends to decrease. Drops were larger than expected when dispensed from the bottle. PRACTICAL IMPLICATIONS/CONCLUSIONS:Drops are larger than expected, so each delivers higher than expected quantities of silver and fluoride. Clinicians should exercise caution when using this product on young children, replace the cap immediately, and use as soon as dispensed.

Quantitative analysis of multi-element concentrations in aqueous solutions, such as water, beverages and biofluids, has long been performed by sequential inductively coupled plasma-mass spectrometry. Recently, a fully simultaneous mass spectrum monitoring ICP-MS instrument that fits a compact Mattauch-Herzog geometry (MH-ICP-MS) with a permanent magnet and a large, spatially resolving semiconductor ion detector has been introduced. This technology allows coverage of the complete inorganic relevant mass range from ⁶Li to ²³⁸U in a single measurement, which helps to mitigate the restriction on the number of inorganic elements whose concentrations may be routinely measured from one sample, thus reducing operational assay times and aqueous sample volumes for evaluations across the breadth of the periodic table. We report here on a detailed method for utilizing MH-ICP-MS to detect all elements of the relevant inorganic spectrum in aqueous samples; 7 types of water, 4 types of beverage, and 4 biofluid biological samples. With this method 71 elements can be routinely detected simultaneously in seconds and in as little as 1-4 mL sample, when using a specific set of calibration and internal standards. Quantitative results reveal distinct element patterns between each sample and within types of samples, suggesting that different types of aqueous solutions can be recognized and distinguished by their elemental patterns. The method has implications for understanding elemental distribution and concentration for many fields, including nutrition, studies of the biosphere, ecological stoichiometry, and environmental health fields, among others, where broad elemental information is actually required.

Our objective is to assess variation in Havers-Halberg oscillation (HHO) periodicities among domestic dogs (Canis familiaris). The HHO is hypothesized to be a hypothalamic-generated biorhythm coordinating multiple life history variables including body mass and lifespan. Dogs have a broad mass range spanning two orders of magnitude, but this variation has been shown to result from selection on very few genetic loci, and dogs have low variation in other life history traits. Therefore, we predict that HHO variation will not be correlated to body mass among domestic dogs, as it is in anthropoid primates. To test the prediction, we examined dog HHO periodicity via manifestations in tooth enamel and dentine, quantifying HHO rhythm histologically. HHO rhythm is reflected in teeth as the number of days between secretion of successive striae of Retzius (enamel) and Andresen lines (dentine), a value referred to as Retzius periodicity (RP). We counted ca. 24-h growth lines between successive Retzius and Andresen lines to determine RP in histological thin-sections from canine teeth of 19 dogs, representing different breeds and sizes. To test our hypothesis, we regressed RP periodicity against body mass data. Dogs have low RP variation for their body mass range, with a modal periodicity of 5 days and a range of 4-6 days. RP was not significantly correlated with body mass. We conclude that mass variation in dogs does not seem driven by HHO physiology, consistent with findings that IGF1 variants produce dog mass variation. However, low RP (and by extension HHO) variation is consistent with low variation in dog lifespan and gestation, suggesting that dog life history may still be governed by HHO mechanisms even if body mass does not reflect this.

It has been argued that the periodicity (in days) between dental enamel growth lines known as striae of Retzius reflects an autonomic biorhythm regulating metabolism and life history. Therefore, quantifying variation in Retzius periodicity (RP) has been recently used as a tool to provide life history and metabolic information among humans, primates, and other mammals. For example, body size is a major driving factor in life history evolution, and correlates strongly with RP in anthropoid primates but not lemurs. Varying datasets disagree as to whether this particular relationship among anthropoid species extends within species, particularly within modern humans. Moreover, little is known regarding the impact that geography has had on life history evolution among modern human populations. Altitude is one unexamined factor that may have influenced this evolution, as high-altitude human populations exhibit multiple adaptations to their relatively hypoxic environment, and low oxygen availability has obvious consequences for overall metabolic output. Therefore, this study uses RP variation to compare a coastal (low altitude) and Andean (high altitude) sample of Pre-Columbian South Americans. We have two major objectives: 1) determine if RP is correlated with body mass within this previously unsampled group, and more importantly; 2) determine if RP differs between coastal and Andean populations, a possible consequence of life history adaptations to altitude. To answer our questions, we gathered teeth from 10 individuals, 5 each from low and high altitude archaeological sites of Peru, all part of the anthropology collection at the American Museum of Natural History. Teeth were cleaned, embedded in acrylic resin, thin-sectioned, and polished according to standard dental histology protocols. They were imaged in circularly polarized light using a Zeiss Axioskop II microscope. Photomicrographs of dental enamel were used to count the number of 24-hour growth lines (cross-striations) between striae of Retzius, indicating the number of days taken to form each successive stria (RP). An average of cross-striation breadths was also divided into an average of striae of Retzius breadths in the same region of each tooth to verify the counted value. For each individual, orbital height and foramen magnum length were used as proxy variables to assess body size. Individuals were sexed based on standard cranial characteristics. Regressions of RP against body size proxies demonstrate a statistically significant negative correlation in the total combined sample. There is no significant difference in RP variation between the sexes, nor in body size between low and high altitude populations. However, the higher altitude population has significantly longer RP values. In conclusion, our analysis suggests that as predicted, an intraspecific relationship exists for RP and body size among our sample, and that altitude elicits as yet unidentified life history/metabolic differences expressed in RP, warranting further study. The high vs. low altitude pattern appears to be independent of the relationship we find between body size and RP in studies of other human populations

Modern humans have smaller faces relative to Middle and Late Pleistocene members of the genus Homo. While facial reduction and differences in shape have been shown to increase biting efficiency in Homo sapiens relative to these hominins, facial size reduction has also been said to decrease our ability to resist masticatory loads. This study compares crania of Homo heidelbergensis and H. sapiens with respect to mechanical advantages of masticatory muscles, force production efficiency, strains experienced by the cranium and modes of deformation during simulated biting. Analyses utilize X-ray computed tomography (CT) scan-based 3D models of a recent modern human and two H. heidelbergensis. While having muscles of similar cross-sectional area to H. heidelbergensis, our results confirm that the modern human masticatory system is more efficient at converting muscle forces into bite forces. Thus, it can produce higher bite forces than Broken Hill for equal muscle input forces. This difference is the result of alterations in relative in and out-lever arm lengths associated with well-known differences in midfacial prognathism. Apparently at odds with this increased efficiency is the finding that the modern human cranium deforms more, resulting in greater strain magnitudes than Broken Hill when biting at the equivalent tooth. Hence, the facial reduction that characterizes modern humans may not have evolved as a result of selection for force production efficiency. These findings provide further evidence for a degree of uncoupling between form and function in the masticatory system of modern humans. This may reflect the impact of food preparation technologies. These data also support previous suggestions that differences in bite force production efficiency can be considered a spandrel, primarily driven by the midfacial reduction in H. sapiens that occurred for other reasons. Midfacial reduction plausibly resulted in a number of other significant changes in morphology, such as the development of a chin, which has itself been the subject of debate as to whether or not it represents a mechanical adaptation or a spandrel.