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Biomedical subjects

A Boyde

Publications and source records attributed to A Boyde.

At least 91 records · Page 5Linked to original sources
PubMed1992

Biocompatibility tests on a novel glass-ceramic system.

The aim of this study was to look at the bone bonding potential of six formulations of a novel glass-ceramic system. Cylinders of the ceramics were implanted in rabbit tibiae for 4 and 7 weeks. Histological tests, both quantitative and qualitative, as well as push-out tests, were carried out during the bonding assessment. Bone growth was quite prolific, even at 4 weeks, as evidenced by growth up to and along the implant surfaces. The interfacial shear strengths compared well with other biomaterials in use as endosseous implants. Therefore it seems pertinent to pursue further long-term experimentation with this material.

Animals↗
PubMed1992

The relationship between the number of nuclei of an osteoclast and its resorptive capability in vitro.

This study examined the relationship between the number of nuclei in an osteoclast and its resorptive efficiency, as demonstrated by the size of the pit it can make in a mineralized tissue in 24 h in vitro. Osteoclasts released mechanically from prehatch chick long bones were cultured on dentine slices or on plastic dishes for periods of 6 or 24 h. The frequency distribution of the multinucleate tartrate-resistant acid phosphatase (TRAP)-positive cells with different numbers of nuclei was determined: the mean number of nuclei per cell was 6.92, with a mode of 4.47% had 5 or fewer nuclei and only 11% more than 10 nuclei. The pits associated with 292 osteoclasts with known numbers of nuclei were measured using a confocal laser light microscope (Lasertec) and dedicated image analysis system, and depths, plan areas and volumes determined. There was a positive correlation between the number of nuclei per osteoclast and the volume of the pit made, but a trend for the volume resorbed per nucleus to decrease with increase in the number of nuclei per osteoclast.

Animals↗
PubMed1992

Three-dimensional images of Ramón y Cajal's original preparations, as viewed by confocal microscopy.

The drawings prepared by Santiago Ramón y Cajal have an inherent beauty as well as being accurate and arose partly as a result of the difficulty contemporary photographic methods had in reproducing informative images of the thick sections he used. Modern methods are better and in this brief article Alan Boyde presents some three-dimensional images of these historical preparations, generated by confocal microscopy.

Animals↗
PubMed1992

Effect of retinoic acid on the resorptive activity of chick osteoclasts in vitro.

Mixed cell suspensions mechanically isolated from the long-bones of day 20 prehatch chicks were cultured for 24 h on bone and sperm whale dentine slices in the presence of 0, 10, 100, and 1000 nM retinoic acid (RA). Significant inhibitions in the numbers of discrete lacunae resorbed per dentine slice, and in the ratio of lacunae per tartrate-resistant acid phosphatase-positive multinuclear cell were observed with all concentrations of RA studied. Semi-automated, 3-dimensional analysis of 733 pits was performed on one series of experiments using a tandem scanning (confocal) microscope, interfaced to an image analyzing computer. The majority of lacunae were small and unilocular; the plan areas of 90% of control pits were below 500 microns 2. Small but statistically significant increases in lacunar areas, but not mean or maximum depths or volumes, were observed in the presence of 10 and 100 nM RA; however, these changes were much smaller than the magnitude of the decrease in pit numbers. Thus, the overall effect of RA in this system was inhibitory. Our findings contrast with the well known stimulatory action of retinoids on bone resorption both in vivo and in organ culture, but may parallel the inhibitory effects of prostaglandins observed in disaggregated osteoclast systems.

Animals↗
PubMed1992

Microscopy of bone cells, bone tissue, and bone healing around implants.

Newer methods of scanning microscopy using both light and electrons are particularly relevant to the study of bone cells, bone matrix organization, matrix mineralization, bone modeling and remodeling, and the adaptation of cells and matrix to implants. Most of such studies are conducted on retrieved implants, at least after the death of the related tissue. Because the retention of the tissue-implant relationship in such preserved tissue is crucial for critical evaluation of the implant, methods based on the study of flat surfaces of embedded tissue blocks are very important. Using electrons, the backscattered electrons in a scanning electron microscope can be employed to evaluate mean atomic number (density) and cathodoluminescence can identify polymers and fluorescent labels. Using light, confocal microscopical techniques permit the examination of layers deep to the block face. Confocal reflected and fluorescence methods allow the study of cell behavior upon both transparent and opaque substrates in the laboratory. Examples of the above are presented and interpretation problems discussed. Current experiments are aimed at enabling the study of bone wound healing and bone adaptation to implanted materials in vivo, through the implantation of optical quality windows and/or newly conceived and designed microscopical objective lenses.

Animals↗
PubMed1992

Analysis of the calcium distribution in predentine by EELS and of the early crystal formation in dentine by ESI and ESD.

Predentine is a collagen-rich extracellular matrix between the odontoblasts and the dentine with a width of about 15-20 microns. Electron energy-loss spectroscopy of rat incisors shows a significantly higher calcium content in the predentine at the predentine-dentine border than in the middle region of the predentine. At the predentine-dentine border in the dentine, the calcium and the phosphate groups combine to form apatite crystallites. Electron spectroscopic diffraction with zero-loss filtering revealed that the earliest crystallites contain only Debye-Scherrer rings of apatite, which are fewer in number and more diffuse than the diffraction rings from the mature crystallites. We therefore conclude that the early crystallites still contain lattice defects, which are annealed out to some degree with crystal growth. Electron spectroscopic imaging with zero-loss filtering also showed that the earliest crystallites are chains of dots (or small islands); they build up strands composed of islands, which rapidly acquire a needle-like character and coalesce laterally to form ribbon-or plate-like crystallites. The parallel strands sometimes appear to reinforce the macroperiod of the collagen microfibrils (67 nm) by tiny holes without any crystal-substance lined up perpendicular to the parallel strands of the crystallites.

Animals↗
PubMed1992

Behaviour of osteoclasts in vitro: contact behaviour of osteoclasts with osteoblast-like cells and networking of osteoclasts for 3D orientation.

The cell-cell contact-induced behaviour of osteoclasts and osteoblasts in vitro was investigated by time-lapse videomicroscopy. Contact interactions of osteoclasts with autologous cells, derived mostly from chick but also from rat bones, included contact inhibition, failure of contact inhibition, contact guidance along stabilised edges of other cells, and underlapping of other cells. Message-mediated contact behaviour (MMCB) between osteoclasts and autologous osteoblastic cells resulted, after a time delay, in zeiosis of the osteoblast-like cell which could continue, or even begin, after the osteoclast broke contact, leading to retraction of the cell and occupation of its position by the osteoclast. MMCB may play a part in the breaching of the osteoblastic sheet by osteoclasts and, in general, in the malignant spread of neoplastic cells. Two or more osteoclasts were often joined by connecting and coordinating tubules (CCTs) of varied, and varying, lengths and widths. Osteoclasts could travel along the CCTs in both directions, or send nuclei through them. The CCTs became temporarily attached to the surface of other cells, or to the substrate, then acting as a temporary anchorage for orientation and for the return of the cell to the same spot. The dynamics of osteoclastic behaviour suggest that such a networking of osteoclasts is valuable for the 3D coordination of their role in bone turnover.

Animals↗
PubMed1991

Analysis of ancient bone DNA: techniques and applications.

The analysis of DNA from ancient bone has numerous applications in archaeology and molecular evolution. Significant amounts of genetic information can be recovered from ancient bone: mitochondrial DNA sequences of 800 base pairs have been amplified from a 750-year-old human femur by using the polymerase chain reaction. DNA recovery varies considerably between bone samples and is not dependent on the age of the specimen. We present the results of a study on a small number of bones from a mediaeval and a 17th-century cemetery in Abingdon showing the relation between gross preservation, microscopic preservation and DNA recovery.

Bone and Bones↗
PubMed1991

Macroscopic shape of, and lamellar distribution within, the upper limb shafts, allowing inferences about mechanical properties.

Collagen orientation maps were determined for the long bones of the upper forelimb (humerus, ulna, radius) using previously described techniques. All three bones had characteristic, non-random patterns of collagen fibre orientation. In the humerus, transverse collagen predominated in the medial and posterior cortices proximally and in the anterior and posterior cortices at the mid diaphysis. In the distal radius, the medial and anterior cortices contained mostly transverse collagen. In the proximal ulna, transverse collagen was found in the anterior and anterolateral cortices. These findings may be correlated to the distribution of bending forces that may be operative in these bones.

Adult↗
PubMed1991

Confocal light microscopic techniques for examining dental operative procedures and dental materials. A status report for the American Journal of Dentistry.

A new form of light microscopy is compared with the current microscopic techniques for examining restorative dental procedures and dental materials. Confocal microscopy enables thin optical sections to be made below the surface of semi-transparent specimens with improved resolution. This paper reviews the different types of confocal microscopes, identifying the strengths and weaknesses of the various instruments. It also reviews some of the techniques for specimen preparation and the control of factors influencing image quality.

Dental Materials↗
PubMed1990

Parathyroid hormone, but not prostaglandin E2, changes the shape of osteoblasts maintained on bone in vitro.

Parietal bones from 2-week-old rats were dissected free from the sutural regions, dura mater, and periosteum, leaving the surface covered with osteoblasts and some osteoclasts. Prostaglandin (PG) production by these "stripped" bones under basal conditions and after exposure to parathyroid hormone (PTH) was measured by radioimmunoassay of the culture medium (minimum essential medium with or without added 10% heat-inactivated fetal calf serum). Cultured specimens were examined by scanning electron microscopy for changes in osteoblast length, orientation, ruffling, and overlap. As demonstrated previously, PTH caused the osteoblasts to elongate, align, and show fewer ruffles compared to controls. PTH increased PG synthesis by the stripped bones. Indomethacin inhibited PG formation but did not affect the osteoblast shape change. PGE2, indomethacin, or both drugs together had no discernible effect on any morphologic features. These findings indicate that PGE2 does not change osteoblast shape and that the cell shape change with PTH is not mediated by endogenous prostanoids.

Animals↗
PubMed1990

The effect of fluoride on the resorption of dentine by osteoclasts in vitro.

Osteoclasts were isolated mechanically from bones of prehatch chicks and cultured on dentine for 24 or 39 h in medium without or with added sodium fluoride at concentrations of 0.15, 1, 15, or 30 mg/liter. Fixed and toluidine blue-stained specimens were examined by light microscopy and osteoclasts were counted, all cells were removed and resorption pits were counted. The dentine was then prepared for scanning electron microscopy (SEM) and pits located on a raster search using backscattered electron imaging. Stereophotogrammetric measurements were made of the depths, plan and true surface areas and volumes of pits, and the volume:area ratio and a three-dimensional form factor calculated for each. The presence or absence of a ring of demineralization around each pit was recorded. Pits with the same plan area were significantly (p less than 0.001) less deep in cultures containing 15 or 30 mg/liter NaF and the incidence of rings around pits was higher (controls 2.7%, 15 mg/liter 31.3%, 30 mg/liter NaF 39.7%). In one experiment, pits were larger in the specimen cultured with added 1 mg/liter NaF, but in a much larger series of 631 (251 in the control and 380 in the 1 mg/liter NaF cultures) pits measured, depths, volumes and volume:plan-area ratios were significantly lower (p less than 0.001), and rings round pits 2.5 times more common, in the fluoride-treated group. A complex interplay of stimulation of some cells in the culture with indirect stimulation of osteoclasts and direct inhibition of osteoclastic resorptive function may be operating at this concentration of fluoride. In vivo, therapeutic doses of sodium fluoride would be expected to act not only to increase the formation of osteoid but also to suppress osteoclastic activity.

Animals↗
PubMed1990

Human cranial bone structure and the healing of cranial bone grafts: a study using backscattered electron imaging and confocal microscopy.

This study explored the microstructure of human cranial bone at different ages, and the survival, remodelling and modelling of cranial bone grafts. A combination of reflection and fluorescence confocal optical microscopy and scanning electron microscopy in the backscattered electron imaging mode was employed to examine highly polished block faces of plastic-embedded bone fragments as harvested for grafting, or recovered after a period in situ as a graft. The methods enabled remarkably detailed information on bone content, maturation and turnover to be gleaned from tiny scraps of bone. Microfractures in the harvested bone were repaired at the graft site, with welding of old and new bone indicating revascularization. Human cranial bone grafts successfully stimulated bone cell differentiation, supported new bone formation on resorbed and unresorbed surfaces, and underwent bone turnover. The type and organization of new bone reflected the growth rate and maturation of the graft rather than the age of the patient.

Adult↗
PubMed1990

SEM study of surface alterations of bioactive glasses and glass--ceramics in a bony implantation bed.

Back scattered electron (BSE) images of glasses and glass-ceramics with different degrees of bone-bonding behaviour have been investigated. After the implantation of probes in the femur of rats changes of the surface material, induced by leaching and corrosion (material response) and of the tissue in the drill hole (host response), were studied. The results demonstrate advantages of using BSE images and give further information for understanding the sequential changes in the implant material which occur mainly in bone-bonding materials. The density of the leached zone was not homogeneous and it therefore might be possible that preferential leaching of the glass matrix contributes to the mineralization of extracellular matrix. These findings could be of use for further development of surface reactive materials.

Animals↗
PubMed1990

The quantitative study of the orientation of collagen in compact bone slices.

We describe and validate a simple method for the study of the proportion of collagen fibers (and apatite crystals) in a bone slice parallel with the plane of section. Viewed between crossed circular polarizers, all bone areas with collagen lying more nearly in the plane of section (i.e., transverse [TS] collagen) appear bright whatever its direction in this plane; longitudinal [LS] collagen appears dark, but not as dark as the background. The degree of brightness increases with section thickness, which must therefore be standardized--we chose 100 microns plane parallel sections. We transferred the circularly polarized light [CPL] image via a CCD TV camera to an image analyzing computer. Color-coded maps of the CPL image were used to compare regions within and between sections. The new analytical procedure makes more detailed studies of the fine-structural orientation in compact bone possible, but does this have any significance? To answer this question, a bone in which the in vivo strain pattern had been clearly documented was chosen for particular study. Transverse mid-diaphyseal sections of the equine radius showed a distribution of CPL bright areas which correlated closely with previously reported strain patterns.

Animals↗
PubMed1990

Regional distribution of mineral and matrix in the femurs of rats flown on Cosmos 1887 biosatellite.

We combined biochemical measurements with novel techniques for image analysis in the rat femur to characterize the location and nature of the defect in mineralization known to occur in growing animals after spaceflight. Concentrations of mineral and osteocalcin were low in the distal half of the diaphysis and concentrations of collagen were low with evidence of increased synthesis in the proximal half of the diaphysis of the flight bones. X-ray microtomography provided semiquantitative data in computer-generated sections of whole wet bone that indicated a longitudinal gradient of decreasing mineralization toward the distal diaphysis, similar to the chemistry results. Analysis of embedded sections by backscattered electrons in a scanning electron microscope revealed distinct patterns of mineral distribution in the proximal, central, and distal regions of the diaphysis and also showed a net reduction in mineral levels toward the distal shaft. Increases in mineral density to higher fractions in controls were less in the flight bones at all three levels, with the most distal cross-sectional area most affected. The combined results from these novel techniques identified the areas of femoral diaphysis most vulnerable to the mineralization defect associated with spaceflight and/or the stress of landing.

Animals↗