Enamel Structure in Primates: A Review of Scanning Electron Microscope Studies

Comparative studies of dental enamel microstructure have involved three main areas of enquiry, with structural features having been investigated in relation to developmental mechanisms, function and/or phylogeny. The phylogenetic, or taxonomic aspect has been emphasized in the majority of studies involving the Order Primates, where efforts have focused upon attempts to recognise structural differences among various hierarchical groups. Studies of primate enamel microstructure by SEM are reviewed here, with emphasis on what has been learned concerning the most suitable preparative techniques that can be employed, and with particular emphasis to the relevance of enamel microstructure in taxonomic analyses of living and fossil primates. No one technique of enamel preparation can be held to be the most suitable for all types of material (e.g., fresh developing, wet mature, dry mature, and fossil enamel) but experience to date allows us to make some recommendations. Two aspects of enamel structure have been shown to possess considerable potential in taxonomic analyses: the enamel prism packing patterns, and the enamel formation rates as documented from prism cross-striation repeat intervals. Although the distribution of enamel prism packing patterns among primates suggests considerable homoplasy of this character, this feature does have considerable taxonomic interest at certain hierarchical levels in Primates. The study of rates of enamel secretion coupled with analyses of enamel thickness has considerable potential in resolving taxonomic and phylogenetic questions

Basis of the Structure and Development of Mammalian Enamel as Seen by Scanning Electron Microscopy

Mature enamel is the most mineralized of mammalian tissues, contains the least water and therefore does not present problems of shrinkage on preparation for SEM. However, the developing enamel is highly hydrated and presents severe problems in preparation. The structure of enamel is determined by the activity of its individual formative cells and their group behaviour. The peculiar, unequal secretion of matrix at the distal pole of the ameloblast leads to the presence of characteristically shaped pits in the surface of the formative tissue. Crystals grow in a special relationship to this surface. Sharp changes in orientation of the surface are reflected in abrupt changes in orientation of neighbouring crystals beneath it, leading to the formation of structural discontinuities at prism boundaries or junctions. Several different patterns of prism cross section have arisen in mammalian enamel. Inequalities in the rate of production of the tissue lead to the formation of features known as varicosities or cross striations. Exaggerations of this presumed daily incremental rhythm lead to the formation of the more major incremental lines which can also be visualized by scanning electron microscopy. Differences in the course of the ameloblasts throughout their life history, in the nature of a translatory motion over the surface which they are secreting, lead to the development of prism decussation, which shows characteristic patterns in different mammalian groups of probable functional significance. One largely ignored area in the study of comparative histology concerns the enamel-dentine junction. Particularly in the marsupial mammals, dentine tubules cross the junction and are continuous with enamel tubules. Methacrylate casting of these features has given new insights into these structures

Observations of High Definition Symmetric Quasi‐Periodic Scintillations in the Mid‐Latitude Ionosphere With LOFAR

We present broadband ionospheric scintillation observations of highly defined symmetric quasi‐periodic scintillations (QPS: Maruyama, 1991, https://doi.org/10.1029/91rs00357) caused by plasma structures in the mid‐latitude ionosphere using the LOw Frequency ARray (LOFAR: van Haarlem et al., 2013, https://doi.org/10.1051/0004‐6361/201220873). Two case studies are shown, one from 15 December 2016, and one from 30 January 2018, in which well‐defined main signal fades are observed to be bounded by secondary diffraction fringing. The ionospheric plasma structures effectively behave as a Fresnel obstacle, in which steep plasma gradients at the periphery result in a series of decreasing intensity interference fringes, while the center of the structures largely block the incoming radio signal altogether. In particular, the broadband observing capabilities of LOFAR permit us to see considerable frequency dependent behavior in the QPSs which, to our knowledge, is a new result. We extract some of the clearest examples of scintillation arcs reported in an ionospheric context, from delay‐Doppler spectral analysis of these two events. These arcs permit the extraction of propagation velocities for the plasma structures causing the QPSs ranging from 50 to 00 m s−1, depending on the assumed altitude. The spacing between the individual plasma structures ranges between 5 and 20 km. The periodicities of the main signal fades in each event and, in the case of the 2018 data, co‐temporal ionosonde data, suggest the propagation of the plasma structures causing the QPSs are in the E‐region. Each of the two events is accurately reproduced using a thin screen phase model. Individual signal fades and enhancements were modeled using small variations in total electron content (TEC) amplitudes of order 1 mTECu, demonstrating the sensitivity of LOFAR to very small fluctuations in ionospheric plasma density. To our knowledge these results are among the most detailed observations and modeling of QPSs in the literature

Observations of High Definition Symmetric Quasi‐Periodic Scintillations in the Mid‐Latitude Ionosphere With LOFAR

We present broadband ionospheric scintillation observations of highly defined symmetric quasi‐periodic scintillations (QPS: Maruyama, 1991, https://doi.org/10.1029/91rs00357) caused by plasma structures in the mid‐latitude ionosphere using the LOw Frequency ARray (LOFAR: van Haarlem et al., 2013, https://doi.org/10.1051/0004‐6361/201220873). Two case studies are shown, one from 15 December 2016, and one from 30 January 2018, in which well‐defined main signal fades are observed to be bounded by secondary diffraction fringing. The ionospheric plasma structures effectively behave as a Fresnel obstacle, in which steep plasma gradients at the periphery result in a series of decreasing intensity interference fringes, while the center of the structures largely block the incoming radio signal altogether. In particular, the broadband observing capabilities of LOFAR permit us to see considerable frequency dependent behavior in the QPSs which, to our knowledge, is a new result. We extract some of the clearest examples of scintillation arcs reported in an ionospheric context, from delay‐Doppler spectral analysis of these two events. These arcs permit the extraction of propagation velocities for the plasma structures causing the QPSs ranging from 50 to 00 m s−1, depending on the assumed altitude. The spacing between the individual plasma structures ranges between 5 and 20 km. The periodicities of the main signal fades in each event and, in the case of the 2018 data, co‐temporal ionosonde data, suggest the propagation of the plasma structures causing the QPSs are in the E‐region. Each of the two events is accurately reproduced using a thin screen phase model. Individual signal fades and enhancements were modeled using small variations in total electron content (TEC) amplitudes of order 1 mTECu, demonstrating the sensitivity of LOFAR to very small fluctuations in ionospheric plasma density. To our knowledge these results are among the most detailed observations and modeling of QPSs in the literature

Inner ear tissue preservation by rapid freezing: improving fixation by high-pressure freezing and hybrid methods

In the preservation of tissues in as ‘close to life’ state as possible, rapid freeze fixation has many benefits over conventional chemical fixation. One technique by which rapid freeze-fixation can be achieved, high pressure freezing (HPF), has been shown to enable ice crystal artefact-free freezing and tissue preservation to greater depths (more than 40μm) than other quick-freezing methods. Despite increasingly becoming routine in electron microscopy, the use of HPF for the fixation of inner ear tissue has been limited. Assessment of the quality of preservation showed routine HPF techniques were suitable for preparation of inner ear tissues in a variety of species. Good preservation throughout the depth of sensory epithelia was achievable. Comparison to chemically fixed tissue indicated that fresh frozen preparations exhibited overall superior structural preservation of cells. However, HPF fixation caused characteristic artefacts in stereocilia that suggested poor quality freezing of the actin bundles. The hybrid technique of pre-fixation and high pressure freezing was shown to produce cellular preservation throughout the tissue, similar to that seen in HPF alone. Pre-fixation HPF produced consistent high quality preservation of stereociliary actin bundles. Optimising the preparation of samples with minimal artefact formation allows analysis of the links between ultrastructure and function in inner ear tissues

Structure and composition of the incisor enamel of extant and fossil mammals with tooth pigmentation

The inclusion of iron compounds in teeth, which impart a red to orange colour to them, is a phenomenon shown by several groups of vertebrates in different periods of their evolution. Incisors from fossil and extant shrews and from extant rodents were sectioned and studied with the techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) to compare their structure and the distribution of Fe. The enamel in white- and red-toothed soricids has three layers; two of them are divided into two zones in the red-toothed species. However, the most external layer varies among taxa; it is well defined in Sorex but difficult to identify in the Early Pleistocene genera Beremendia or Dolinasorex. In the arvicoline rodent Terricola, only two layers can be defined, the outer of which is divided into two zones depending on the presence or absence of Fe. The Fe proportions in the larger soricids reach up to 45%, but in rodents only up to 10% (weight % with respect to Fe + Ca + P). The STEM study shows that in a fossil soricid the Fe phases form clusters of nanometric particles of very poor crystalline oxides or hydroxides surrounding the apatite crystals that form the enamel

The plate-to-rod transition in trabecular bone loss is elusive.

Changes in trabecular micro-architecture are key to our understanding of osteoporosis. Previous work focusing on structure model index (SMI) measurements have concluded that disease progression entails a shift from plates to rods in trabecular bone, but SMI is heavily biased by bone volume fraction. As an alternative to SMI, we proposed the ellipsoid factor (EF) as a continuous measure of local trabecular shape between plate-like and rod-like extremes. We investigated the relationship between EF distributions, SMI and bone volume fraction of the trabecular geometry in a murine model of disuse osteoporosis as well as from human vertebrae of differing bone volume fraction. We observed a moderate shift in EF median (at later disease stages in mouse tibia) and EF mode (in the vertebral samples with low bone volume fraction) towards a more rod-like geometry, but not in EF maximum and minimum. These results support the notion that the plate to rod transition does not coincide with the onset of bone loss and is considerably more moderate, when it does occur, than SMI suggests. A variety of local shapes not straightforward to categorize as rod or plate exist in all our trabecular bone samples

Process evaluation of a randomised pilot trial of home-based rehabilitation compared to usual care in patients with heart failure with preserved ejection fraction and their caregiver’s

Background: Whilst heart failure (HF) with preserved ejection fraction (HFpEF) affects almost 50 percent of the HF population, evidence-based treatment options remain limited. However, there is growing evidence of the potential value of exercise-based cardiac rehabilitation. This study reports the process evaluation of the Rehabilitation Enablement in Chronic Heart Failure (REACH-HF) intervention for HFpEF patients and their caregivers conducted as part of the REACH-HFpEF pilot trial. Methods: Process evaluation sub-study parallel to a single centre (Tayside, Scotland) randomised controlled pilot trial with qualitative assessment of both intervention fidelity delivery and HFpEF patients’ and caregivers’ experiences. The REACH-HF intervention consisted of self-help manual for patients and caregivers, facilitated over 12 weeks by trained healthcare professionals. Interviews were conducted following completion of intervention in a purposeful sample of 15 HFpEF patients and 7 caregivers. Results: Qualitative information from the facilitator interactions and interviews identified three key themes for patients and caregivers: (1) understanding their condition, (2) emotional consequences of HF, and (3) patients’ and caregivers’ responses to the REACH-HF intervention. The differing professional backgrounds demonstrate the possibility of delivering REACH-HF by either existing HF or cardiac rehabilitation services of a combination of the two. Conclusions: The REACH-HF home-based facilitated intervention for HFpEF appears feasible and well accepted model for delivery of a cardiac rehabilitation intervention, with the potential to address key unmet needs of patients and their caregivers who are often excluded from service provision and current CR programmes. Results of this study will inform a recently funded full multicentre randomised clinical trial