Faculty Bibliography

Linear enamel hypoplasia (LEH) appears as pronounced horizontal grooves on the outer surface of teeth. LEH defects are understood to represent episodes of nonspecific stress in early life, but little is known about their etiology in nonhuman primates. Researchers have suggested that more severe stressors result in deeper LEH defects, while others argue that depth is related to enamel geometry, i.e., larger or smaller striae angles, reflecting differences in growth rates. Here we ask whether inter- and intraspecific variation in enamel growth corresponds with documented differences in defect depth among great apes. Enamel extension rate (EER), or the rate at which teeth grow in height, was assessed using histological methods in canines of four taxa (Gorilla beringei, Gorilla gorilla, Pan troglodytes, Pongo sp., N=16). While sample sizes are too small for statistical comparisons, mountain gorillas have faster EER, and show no overlap with other taxa in the middle 3/5ths of crown height, where LEH defects most commonly occur. This matches our previously reported pattern of defect depth, with mountain gorillas having shallower defects than other taxa in the same crown region. In general, males have faster extension rates than females, but there is some overlap, particularly outside the midcrown. We found that EER is negatively correlated with defect depth (r2=0.66, p<0.001). These results suggest that enamel growth variation influences LEH defect morphology, with faster-growing crowns having shallower defects. However, stress severity may also play an important role in defect formation and help to explain the appearance of particularly deep defects

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.

Various natural patterns-such as terrestrial sand dune ripples, lamellae in vertebrate bones, growth increments in fish scales and corals, aortas and lamellar corpuscles in humans and animals-comprise layers of different thicknesses and lengths. Microstructures in manmade materials-such as alloys, perlite steels, polymers, ceramics, and ripples induced by laser on the surface of graphen-also exhibit layered structures. These layered patterns form a record of internal and external factors regulating pattern formation in their various systems, making it potentially possible to recognize and identify in their incremental sequences trends, periodicities, and events in the formation history of these systems. The morphology of layered systems plays a vital role in developing new materials and in biomimetic research. The structures and sizes of these two-dimensional (2D) patterns are characteristically anisotropic: That is, the number of layers and their absolute thicknesses vary significantly in different directions. The present work develops a method to quantify the morphological characteristics of 2D layered patterns that accounts for anisotropy in the object of study. To reach this goal, we use Boolean functions and an N-partite graph to formalize layer structure and thickness across a 2D plane and to construct charts of (1) "layer thickness vs. layer number" and (2) "layer area vs. layer number." We present a parameter disorder of layer structure (DStr) to describe the deviation of a study object's anisotropic structure from an isotropic analog and illustrate that charts and DStr could be used as local and global morphological characteristics describing various layered systems such as images of, for example, geological, atmospheric, medical, materials, forensic, plants, and animals. Suggested future experiments could lead to new insights into layered pattern formation.

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.

This study evaluated the influence of polishing protocols on the surface roughness of flowable and regular bulk fill composites. Five bulk fill composites were tested: SureFil SDR Flow (SDR), Tetric EvoFlow Bulk fill (TEF), Filtek Bulk Fill Flowable (FIF), Tetric EvoCeram Bulk Fill (TEC), and Filtek Bulk Fill Posterior (FIP). Two polishing protocols were tested: Sof-Lex and Astropol. Astropol created a smoother surface for FIP (P < .05); however, the polishing protocol did not influence surface roughness on TEC (P > .05). SDR, TEF, and FIF exhibited rougher surfaces when polished. Sof-Lex created rougher surfaces for bulk fill composites. It was concluded that surface roughness was related to material composition rather than the polishing system.

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.

Recent studies have demonstrated matrix-mineral alterations in bone tissue surrounding osteocytes in estrogen-deficient animals. While cortical bone porosity has been shown to be a contributor to the mechanical properties of bone tissue, little analysis has been done to investigate the effects of estrogen deficiency on bone's microporosities, including the vascular and osteocyte lacunar porosities. In this study we examined alterations in cortical bone microporosity, mineralization, and cancellous bone architecture due to estrogen deficiency in the ovariectomized rat model of postmenopausal osteoporosis. Twenty-week-old female Sprague-Dawley rats were subjected to either ovariectomy or sham surgery. Six weeks post-surgery tibiae were analyzed using high-resolution micro-CT, backscattered electron imaging, nanoindentation, and dynamic histomorphometry. Estrogen deficiency caused an increase in cortical bone vascular porosity, with enlarged vascular pores and little change in tissue mineral density in the proximal tibial metaphysis. Measurements of cancellous architecture corresponded to previous studies reporting a decrease in bone volume fraction, an increase in trabecular separation, and a decrease in trabecular number in the proximal tibia due to estrogen deficiency. Nanoindentation results showed no differences in matrix stiffness in osteocyte-rich areas of the proximal tibia of estrogen-deficient rats, and bone labeling and backscattered electron imaging showed no significant changes in mineralization around the vascular pores. The findings demonstrate local surface alterations of vascular pores due to estrogen deficiency. An increase in cortical vascular porosity may diminish bone strength as well as alter bone mechanotransduction via interstitial fluid flow, both of which could contribute to bone fragility during postmenopausal osteoporosis.