David Mills

By the commonly accepted rules of nomenclature, cells forming hard tissue which become incorporated within the inter- and extra-cellular tissue mass which they secrete are called ‘-cytes’: the spaces in which these cells sit are called lacunae. Hence, osteoblasts become osteocytes in osteocytic lacunae, chondroblasts become chondrocytes, cementoblasts cementocytes, even odontoblasts become odontocytes in some mammalian species. We provide evidence that enamel spindles are cell bodies of ameloblasts which have become entrapped and buried in the enamel matrix produced by the surrounding cells, to produce amelocytic lacunae: it is no life for a cell in a rigid, dense and dead tissue, and we do not suppose that amelo cytes live once they are set on that route. Spindles, normally only found at the enamel-dentine junction, are absent when the enamel at the junction is free of prisms, i.e., the ameloblasts had no Tomes’ processes. Spindles have an organic content, the amelocyte residue which can be stained - and removed by bleach, after which the spindle space no longer stains. Spindles are extensions of enamel tubules which result from the extension of a fine ameloblastic process [from the major Tomes’ process] which unites with an odontoblast process. In marsupial mammals, the spindle-like ends of the enamel tubules are commonly located well within the enamel. Spindles/amelocytes may form at the neonatal line in human deciduous teeth in cases of severe neonatal stress, and these features simply represent encapsulation of moribund ameloblasts. The frequency of spindles at the enamel dentine junction is greater in cases where the tooth germ is severely deformed by growth pressure from the forming root of a neighbouring tooth.

Although healthy teeth are never really white, bleaching agents are used cosmetically to whiten teeth. We studied the in vitro effects of some bleaching agents and acids on the Vickers Hardness (VH) of human dental enamel using a 100 gram [981 mN] load applied for 15 s and examined treated surfaces with backscattered electron mode scanning electron microscopy (BSE SEM; 20 kV, uncoated, chamber pressure 50 Pa). Rows of indents were made in the untreated condition and intervening rows placed after treatment. Thus, the samples served as their own controls. Gel bleaching agents − 35% hydrogen peroxide or carbamide peroxide - and 30% hydrogen peroxide solutions caused substantial reductions in microhardness. Weaker peroxide gels and solutions caused lesser changes. A 5% available chlorine sodium hypochlorite bleach treatment resulted in no significant change. Prism boundary discontinuities in flat polished surfaces are normally thin and dark in BSE-SEM imaging because of the lower mineral content in the region where crystallite orientation changes abruptly – they are also not joined up. Strong peroxide bleached surfaces, however, showed wider, whiter and conjoined boundaries as in acetic acid treated samples. This appearance is the hallmark of subsurface demineralisation and remineralisation, wherein the boundary region is widened and extended by dissolution of mineral, with reprecipitation of dissolved mineral in surrounding partially demineralised tissue and infilling of the original boundary defect. Identical sequences are identified in natural and artificial carious lesions and in acid etched enamel. This appearance was not generated by 6% peroxide gel. The softening of enamel by peroxide bleaching agents is explained both by the removal and redistribution of the hard mineral phase, accounted for by their acidic (i.e. low pH) nature; and the removal of the enamel protein matrix ‘glue’ holding the crystallites together.

Armadillos are bitten by several species of flea. Females of the genus Tunga penetrate the epidermis and when in place are fertilised by males, after which the abdomen swells enormously to form a ‘neosome’. Within the penetrans group, T. perforans, makes lesions that perforate the osteoderms within the integument to form ~3 mm diameter cavities occupied by a discoid neosome. We examined these lesions in carapace material from animals which had died in the wild to see whether we could recruit evidence as to how they may be generated, either by the insect or by the host. We studied one species without such lesions, the nine‐banded armadillo Dasypus novemcinctus, and two species with, the greater hairy armadillo Chaetophractus villosus and the southern three‐banded armadillo Tolypeutes matacus, both showing the characteristic ‘flea bite’ holes in the external surfaces of the osteoderms. Samples were studied by three‐dimensional backscattered electron mode scanning electron microscopy and X‐ray microtomography. Both methods showed resorption pit complexes in the external surfaces of the osteoderms characteristic of those made by osteoclasts in active bone resorption. Lesions involved both the syndesmoses (sutures) between adjacent bones and the central regions of the osteoderms. Many lesions showed extensive repair by infilling with new bone. We conclude that the T. perforans neosome creates a local host response which causes bone resorption, creating the space in which it can grow.

The materials used in producing books are almost exclusively natural or synthetic polymers, formed by linking large numbers of small molecules to form long chains, which may be linear, branched, or form networks. This chapter outlines the chemistry of the important polymers, particularly polysaccharides, proteins, lignin, and synthetic materials, emphasising how the chain structure affects chain packing in the solid state and thus mechanical properties. Because these materials are organic molecules, they are susceptible to degradative influences, notably heat, oxygen, light, moisture, and microorganisms, all of which can cause chain scission, or crosslinking, and loss of mechanical properties, as well as development of colour. The chemistry of the various degradation reactions and their effects on both physical properties and appearance are reviewed for the important polymer types. As well as specific materials, degradation can be influenced by catalytic contact with other materials, like metals, by small molecules in the materials, such as pigments and plasticisers (notably water) in natural polymers, and by external pollutants in the local environment (important in storage). These effects are also reviewed.

Computational flattening algorithms have been successfully applied to X-ray microtomography scans of damaged historical documents, but have so far been limited to scrolls, books, and documents with one or two folds. The challenge tackled here is to reconstruct the intricate folds, tucks, and slits of unopened letters secured shut with “letterlocking,” a practice—systematized in this paper—which underpinned global communications security for centuries before modern envelopes. We present a fully automatic computational approach for reconstructing and virtually unfolding volumetric scans of a locked letter with complex internal folding, producing legible images of the letter’s contents and crease pattern while preserving letterlocking evidence. We demonstrate our method on four letterpackets from Renaissance Europe, reading the contents of one unopened letter for the first time. Using the results of virtual unfolding, we situate our findings within a novel letterlocking categorization chart based on our study of 250,000 historical letters.

It is presently unclear why there is a high prevalence of periodontal disease (PD) in individuals living with chronic kidney disease (CKD). By employing three different models in rats and mice, we demonstrate that experimental uremia causes periodontal bone loss. Uremia alters the biochemical composition of saliva and induces progressive dysbiosis of the oral microbiota, with microbial samples from uremic animals displaying reduced overall bacterial growth, increased alpha diversity, reduced abundance of key components of the healthy oral microbiota such as Streptococcus and Rothia, and an increase in minor taxa including those from gram-negative phyla Proteobacteria and Bacteroidetes. We show that transfer of oral microbiota from uremic mice induces PD in germ-free animals, whilst co-housing with healthy animals ameliorates the PD phenotype in rats. Thus, we advocate that periodontal disease should be regarded as a bacterially mediated complication of chronic uremia.

The feasibility of a thin-wire torsion stress-strain experiment with nanostrain sensitivity is demonstrated. A gauge length of 50 m was made possible by using The Monument, London, thereby restoring it to its original purpose as a scientific instrument. A wire of 150 μm diameter was studied using the load-unload method, and data were recorded in the elastic regime and through the elastic-plastic transition. Analysis of this preliminary experiment suggested some necessary improvements to the equipment and methods. Progress towards definitive experiments is described together with difficulties still to be overcome.

There is a large body of historical documents that are too fragile to be opened or unrolled, making their contents inaccessible. Recent improvements in X-ray scanning technology and computer vision techniques make it possible to perform a “virtual” unrolling of such documents. We describe a novel technique to process a stack of 3D X-ray images to identify the surface of parchment scrolls, unroll them, and create a visualization of their written contents. Unlike existing techniques, we can handle even challenging cases with minimal manual interaction. Our novel approach was deployed on two 15th and 16th century damaged historic scrolls from the manors of Bressingham and Diss Heywood. The former has become fused, probably due to exposure to moisture, and cannot be fully unrolled. The latter was severely burnt several hundred years ago, becoming thoroughly charred, heat-shrunken, and distorted, with all the sheets now brittle and fused together. Our virtual unrolling revealed text that has been hidden for centuries.