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Biomedical subjects

A Boyde

Publications and source records attributed to A Boyde.

At least 127 records · Page 7Linked to original sources
PubMed1987

Colour-coded stereo images from the tandem scanning reflected light microscope (TSRLM).

A method is described for the production of stereo-pair images in the tandem scanning reflected light microscope in which depths within the field imaged are coded in colour. The two images are recorded photographically whilst focusing vertically through the layer which is to be imaged. A horizontal component of motion is applied at the same time, but in opposing senses for the two images. Colour coding for depth is obtained by changing colour filters so that reflective features lying within different depth bands are imaged in corresponding colours.

Animals↗
PubMed1987

Tandem scanning reflected light microscopy of primate enamel.

Studies of the cross sectional packing arrangements of primate enamel prisms have been used in a number of recent studies in attempts to determine their taxonomic utility. Credibility of the results has been greatly influenced by the methods employed to examine enamel prism packing patterns and also by the limited sampling. We report here the use of a technique for the non destructive examination, in depth, of enamel prism packing patterns in modern and fossil primate teeth which has considerable advantages over any others so far used, and the preliminary results of a survey of enamel structural diversity in the Order Primates. The phylogenetic implications of these findings are also discussed. A novel microscope, the Tandem Scanning Reflected Light Microscope (TSM) has been used. This instrument has allowed these data to be obtained non destructively which has permitted the inclusion of rare fossil primates in this survey. The technique has many advantages relating to the interpretation of the results as the specimens are not etched or otherwise prepared. Primates exhibit all three major prism packing arrangements known for recent mammals. The distribution of these permits the recognition of haplorhine from strepsirhine primates and also cercopithecoid monkeys from other catarrhines.

Animals↗
PubMed1987

Tandem scanning reflected light microscopy: applications in clinical dental research.

The Tandem Scanning Reflected Light Microscope (TSRLM) enables the investigation of microscopic structures both at and deep to the surface of intact objects. The present paper reviews studies undertaken to determine whether the TSRLM would be usable and useful in the investigation of natural and restorative dental materials in vitro and in vivo. It was found that the TSRLM could be used to study normal and diseased dental tissues and the new materials which are used to replace lost substance. More importantly, it could be used to characterize the interface between tooth and optically translucent materials in bulk samples, giving high resolution information from not only a shallow depth of field, but at planes below cut surfaces. This makes it possible to study interfacial regions in three dimensions without the risk of delamination that must accompany the preparation of a microscopic section. The use of fluorescent markers enables more information to be derived from the tooth/adhesive interface. Studies to date indicate the need for the development of adhesion promoting agents which incorporate a fluorescent radical in their molecular structure. Preliminary work using the instrument for observation of cutting interactions between a high speed bur and a tooth indicates some useful potential in the study of cavity preparation techniques and tissue failure mechanisms. Recent developments of the TSRLM for three dimensional imaging in other dental applications are outlined. This microscope is an important advance in the microscopic assessment of adaptation of biomaterials to hard tissues.

Animals↗
PubMed1987

Scanning microscopic observations on dental caries.

This paper presents findings made using special techniques of imaging and/or of specimen preparation to investigate the changes in tooth structure which occur in caries. We have studied both coronal and root caries in enamel, dentine and cementum using scanning electron and confocal scanning optical microscopy. In preparation for backscattered electron (BSE) imaging in the SEM, teeth were stored in 70% ethanol until further dehydration in ethanol and embedding in polymethylmethacrylate (PMMA). Longitudinally cut surfaces were diamond polished and coated with carbon or silver before BSE imaging. Important changes in the distribution of densities in both enamel and dentine occurred during caries, and could be correlated with prior published studies using polarised light and microradiography to study demineralization in these tissues. However, the resolution of the BSE imaging technique is much higher than that of these previous methods. A new method was used for demonstrating local variations in microhardness with special relevance to the changes occurring in dental caries. Sectioned surfaces were subjected to treatment with a jet of soft abrasive particles, resulting in the selective removal of carious enamel, and enhanced removal of carious dentine. The tandem scanning reflected light microscope (ISRLM) has also been shown to be useful in characterising the spread of caries in the dental tissues. Teeth only need to be cut once, because the image is formed on looking into a bulk specimen. Fluorescent dyes can be used to study the distribution of pore volume, making use of the high resolution in depth of this confocal microscope.

Dental Caries↗
PubMed1987

Early scanning electron microscopic studies of hard tissue resorption: their relation to current concepts reviewed.

This paper highlights some observations made by the authors in SEM studies of hard tissue resorption and considers their significance in relation to current concepts. All mammalian mineralised tissues may undergo physiological resorption, the resulting surface reflecting the density of mineralisation and the organic matrix chemistry, organisation and orientation. Resorption-repair coupling may follow the resorption of any tissue, but SEM studies first noted this process in the case of the dental tissues. The difference between fetal and adult bone formation and resorption provided evidence against the concept of osteocytic osteolysis. SEM stereophotogrammetric methods for the quantitation of individual resorption lacunae are now much quicker and have been extended to the study of in vitro resorption by mammalian and avian osteoclasts isolated from bone and seeded into new substrates. Experimental studies using SEM were first conducted on the osteotropic hormonal effects on bones forming in vivo and extended to the in vitro situation. The effects observed underlined the several actions of PTH on osteoblasts and indicated their important role in the control of bone resorption. Immunological marking techniques monitored by SEM first established that osteoclasts had no Fc or C3 receptors, although other cells in the vicinity did. The study of osteoclasts resorbing substrates other than bone in vitro has increased our understanding of the essential components of a resorbable substrate. Experiments growing separated bone cells and marrow cells on calcified substrates have shown that such cells will continue to resorb for at least six weeks.

Adult↗
PubMed1987

Marsupial and monotreme enamel structure.

We present some recent developments in our understanding of two basic questions: the origin, extent, nature and course of marsupial enamel tubules; and the characterisation of monotreme enamel, more particularly, the prismatic nature of platypus enamel. Methods used included SEM of methacrylate casts of marsupial enamel tubules, worn and cut surfaces of whole marsupial teeth, developing and erupted platypus teeth, and a well-developed molar of the newly discovered Miocene ornithorhynchid Obdurodon sp., and tandem scanning reflected light microscopy of intact marsupial teeth. We conclude that there are significant species differences with respect to prism shape, row formation and tubule disposition in marsupials and, moreover, that these features change in a consistent way through the thickness of the enamel. Consideration of enamel prism course in incisor and molar enamel of Macropus eugenii, together with the tubule casts, enables us to conclude that there is a fundamental relationship of tubule to prism in the body of marsupial enamel. This and previously reported data put beyond dispute the essential relationship of the marsupial tubule to the formative ameloblast. The enamel of Ornithorhynchus anatinus is shown to be prismatic only in part, with well-formed regular prisms not being a primary structural feature. The enamel of the fossil monotreme is prismatic and tubular and displays large areas of Pattern 2 prism packing. Monotreme enamel has been interpreted as representing a structural stage intermediate between that of known multituberculates and extant tribosphenid mammals.

Animals↗
PubMed1987

Mineralization of normal and rachitic chick growth cartilage: vascular canals, cartilage calcification and osteogenesis.

This paper reviews recent work in the authors' laboratories that has led to new observations and thoughts concerning the mineralization of normal and rachitic chick growth cartilage. The proximal tibial growth cartilages of normal and rachitic chicks were rapidly frozen and prepared for SEM and biochemical studies. Using a scanning microfluorimetric technique we showed that at the mineralization front of normal and rachitic cartilage there is an abrupt change in chondrocyte metabolism. Thus cells in this region exhibited an increase in NADH and oxidative metabolism. In rickets, there was a decrease in the reduced pyridine nucleotide content of each of the zones. The reversal in chondrocyte metabolism was not due to low oxygen tension. SEM observations indicated that this region of cartilage was well supplied with vascular channels; moreover, mineral was first seen deposited in matrix in close proximity to the blood supply. Indeed these vascular channels appeared to be a basic architectural feature of normal cartilage, although disorganized in the rachitic state. The morphological studies also showed that gaps existed in the continuity of the mineral phase in normal cartilage. Although the rachitic cartilage does mineralize, discontinuities in the mineral distribution are much more severe, with the general failure of fusion of adjacent mineral clusters. These structures would serve as pathways for transport of nutritional factors and gases to chondrocytes that are distant from the vascular channels. Observation of hypertrophic cells reinforced the view that some osteoblasts represented a terminal stage in the maturation of chondrocytes.

Animals↗
PubMed1986

Scanning microscopy of platypus teeth.

Anorganic unerupted developing teeth and air-dried erupted teeth of the platypus (Ornithorhynchus anatinus) were examined in a scanning electron microscope and in a tandem scanning reflected light microscope. Typically mammalian developing fronts of enamel and dentine were identified in the anorganic unerupted specimens. The developing teeth were particularly small and fragile and the enamel elusive and difficult to examine in the normal way for morphological detail. Prepared fractured surfaces of unerupted specimens revealed preferentially oriented crystallite groups in the enamel generally perpendicular to the developing front and a highly globular, mineralized pattern in the dentine with fine diameter, sparsely distributed dentinal tubules. Although optically homogeneous, the enamel of both developing and mature teeth displayed well-defined incremental lines, radial clefts, crystallite domains of variable size and outline, and fine tubules when examined by high contrast, back-scattered electron imaging. The enamel is prismatic only in part; well-formed, regular prisms not being a primary feature of platypus enamel. This can be related to the variability inherent in the developing surface and the thinness of the enamel layer. No surface was found which could be confidently identified as cementum; those developing surfaces not covered by enamel displaying small calcospherites which elsewhere marked the outer aspect of the dentine.

Animals↗
PubMed1986

Distribution of capillaries in relation to the life cycle of odontoblasts in the rat incisor. The fate of the pulp at the incisal end.

Although the rat incisor is used widely in the study of dentinogenesis there is little information on the pulp capillaries and the fate of the pulp contents incisally. The capillaries have now been described in relation to the life cycle of the odontoblasts using light microscopy on perfusion fixed teeth and SEM on pulp vascular casts. Odontoblast precursors differentiated to preodontoblasts in the absence of local vessels. Capillaries entered the zone subjacent to preodontoblasts prior to their transformation to odontoblasts. They invaded the odontoblast layer after formation of odontoblast processes and during lengthening of their cell bodies. These capillaries formed a dense plexus which was separated from the predentine by about 10 micron thickness of odontoblast cytoplasm. Electron microscopy near the incisal end showed that the odontoblasts lost their processes and their polarity to form postodontoblasts. This coincided with the deposition of atubular collagenous tissue at the periphery of the pulp. Loss of fenestrations in the capillaries seemed to coincide with the diminution of odontoblast function. Odontoblastic capillaries were lost before the postodontoblasts became separated from one another. There was evidence of degenerating vessels, cells and extracellular debris near the incisal end. Light and transmission electron microscopical evidence from demineralised teeth was correlated with SEM evidence from anorganically prepared specimens and considered in relation to dynamic events at the incisal surface. Thus the pulp closure region was found to include a central zone of mineralised, moribund pulp cells and debris surrounded by atubular tissue.

Aging↗
PubMed1986

Survival and resorptive activity of chick osteoclasts in culture.

Previous studies have shown that osteoclasts obtained from chopped bones resorb surrogate calcified tissue substrata in vitro. These cultures contained all bone and marrow cell types pooled together. We have now parted the marrow from the bone and cultured the cells from the two fractions separately: on both resorbable substrates and on plastic in order to test their longevity in culture and ability to resorb following trypsinisation. Marrow-fraction, bone-fraction or whole bone derived cells were harvested from prehatch chick long bone shafts after removing the periosteum; seeded on sperm whale dentine (SWD) slices or plastic dishes and cultured continuously, or trypsinised and reseeded on to fresh substrata at weekly or half-weekly intervals. Observations were made by light microscopy and SEM. Many multinucleate cells were observed in the marrow fraction immediately after settling, deriving presumably from poorly adherent osteoclasts, next to bone, which had not been resorbing at the time of harvesting. By three days in culture on plastic, multinucleate cells were very large both in terms of plan extent and nuclear number: cell fusion occurred between osteoclasts and between osteoclasts and small, round uninuclear cells. SWD was extensively resorbed. The adherence of the osteoclasts was greater (a) to plastic upon trypsinisation than that of the other cells; and (b) to SWD than to plastic, particularly if the cells were resorbing. Trypsinised cells regained their resorptive capacity after seeding on to new SWD, but only for 1 or 2 treatments. Bone derived cells were similar to the marrow cultures, except for the much higher proportion of other bone cell types. Trypsinisation caused a higher proportional loss of multinucleate cells from both SWD and plastic. Resorption was still occurring at 6 weeks in all cultures. A wide diversity existed in the shapes, depths, plan areas and volumes of the resorption pits.

Animals↗
PubMed1986

Simple SEM stereophotogrammetric method for three-dimensional evaluation of features on flat substrates.

A semi-automated method was developed for the measurement of the volume of a calcified tissue substrate which can be resorbed by single, isolated resorptive cells (osteoclasts). The procedure would, however, be applicable to the study of any pit in, or projection from, a flat surfaced specimen. Stereo-pair images are recorded with an SEM. 3-D co-ordinates of relevant surface features are derived using a stereo-comparator which outputs data directly to a microcomputer. Algorithms adopted have been chosen to give the best compromise between accuracy and speed of data acquisition.

Animals↗
PubMed1986

Scanning electron microscopy in bone pathology: review of methods, potential and applications.

This article reviews the applications of SEM methods to human bone pathologies referring to studies made at UCL. We consider the methods which may be most suitable; these prove to be not "routine" in the context of most bio-medical applications of SEM. Valuable information can be obtained from a bone sample if its edges are ground flat, before making either a matrix surface preparation by washing away all the cells or a mineralizing front preparation, by also dissolving the osteoid-for which hydrogen peroxide is recommended to produce a robust specimen. BSE contrast from a cut block surface can be used to measure bone phase volume. SE contrasts from natural surfaces (trabeculae, canals and lacunae) can be used to study forming, resting and resorbing surfaces both qualitatively and quantitatively (except in the case of histological osteomalacia, where the existence of osteoid will go undetected and reversal lines will be difficult to distinguish from recently resorbed surfaces). We also recommend the use of PMMA embedded bone blocks, which can be used as obtained from the pathologist, but are better embedded by a more rigorous procedure. BSE image analysis can be used to quantitate bone density fractions opening up a completely new investigative method for the future. Osteoid can be measured automatically using CL if the bone sample is block stained with brilliant sulphaflavine before embedding or if a scintillant is added to the embeddant. We give examples of observations made from a number of bone diseases: vitamin D resistant rickets, osteogenesis imperfecta; osteomalacia; osteoporosis; hyperparathyroidism; fluorosis; Paget's disease; tumour metastasis to bone.

Adolescent↗