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Biomedical subjects

S Bryant

Publications and source records attributed to S Bryant.

At least 37 records · Page 2Linked to original sources
PubMed1997

Shaping ability of the M4 handpiece and Safety Hedstrom files in simulated root canals.

The aim of this study was to assess the shaping ability of the M4 reciprocating handpiece and Safety Hedstrom files in simulated canals. A total of 40 simulated canals of various angles and positions of curvature were prepared with an M4 handpiece using Safety Hedstrom files oriented with the ground, flattened surface towards the inner aspect of the curve. A standard regimen was adopted throughout. Pre- and post-operative longitudinal images of the canals were taken with a video camera and stored and manipulated in a computer with image analysis software. The presence of canal aberrations and the amount and location of resin material removed as a result of preparation were determined from composite images of superimposed pre- and post-operative views. Preparation time varied significantly (P < 0.001) between the canal types; overall, 20 degrees canals were prepared more quickly than 40 degrees canals. Zips and elbows were observed in 16 out of the 40 canals with most (11) being created in 40 degrees specimens. Ledges were found in 19 canals and perforations in only 1. There were no significant differences between canal shapes for these aberrations. Excessive removal of material from the inner aspect of the canal at the curve to create a danger zone was found in 20 canals, but only in those with 40 degrees curves. Significant differences in total canal width between the canal types were seen at the zips (P < 0.05), elbows (P < 0.05) and danger zones (P < 0.001). Transportation at the danger zones varied significantly (P < 0.001) between canal types. Under the conditions of this study, the M4 handpiece and Safety Hedstrom files created hour-glass preparations in a substantial proportion of canals. In reality, the Safety Hedstrom file with its one flattened surface was ineffective at reducing removal of material along the inner aspect of canal curves in severely curved specimens and clearly has the potential to create strip perforations in teeth.

Analysis of Variance↗
PubMed1997

Comparison of two stainless steel files to shape simulated root canals.

The aim of this study was to compare the shaping ability of two stainless steel files using simulated canals. A total of 80 simulated canals of various angles and positions of curvature were prepared by hand using either Mani K-Files or Micro Mega K-Files. Following orifice enlargement each file type was used to prepare 40 canals employing a linear filing motion and an anticurvature stepback technique. Pre- and post-operative longitudinal images of the canals were taken with a video camera and stored and manipulated in a computer with image analysis software. The presence of canal aberrations and the amount of material removed as a result of preparation were determined from composite images of superimposed pre- and post-operative views. Overall, canal preparation with Mani K-Files was significantly quicker (P < 0.005) and was associated with fewer instrument failures. Zips and elbows were observed in 70% of specimens with significantly more (P < 0.05) occurring following preparation with Micro Mega K-Files. Mani K-Files created significantly more (P < 0.01) danger zones. Micro Mega K-Files created significantly wider (P < 0.001) zips with significantly more (P < 0.01) resin removed from the outer aspect of the curves and, thus, significantly more (P < 0.01) transportation. Canal shape had a significant influence on preparation time (P < 0.001), the incidence of zips (P < 0.05) and danger zones (P < 0.005), the width of zips (P < 0.001) and transportation at the zips (P < 0.001). Under the conditions of this study, Mani K-Files were more effective than Micro Mega K-Files and produced canals with better shapes. Original canal shape had a substantial influence on the outcome of shaping procedures.

Analysis of Variance↗
PubMed1997

Cutaneous leiomyomas lack estrogen and progesterone receptor immunoreactivity.

Gonadotropin-releasing hormone analog therapy is useful in treating uterine and some extrauterine smooth muscle tumors. These smooth muscle tumors have been demonstrated to have estrogen receptor and progesterone receptor immunoreactivity. The estrogen receptor and progesterone receptor immunoreactivity of smooth muscle tumors of the skin has not been reported. We evaluated 15 examples of cutaneous leiomyomas for estrogen receptor and progesterone receptor with ER-1D5 antibody and PGR-1A6 antibody. None of the 15 cutaneous leiomyomas demonstrated positive staining by this method. The tumorigenesis of cutaneous leiomyomas does not appear to be related to estrogen or progesterone receptor-mediated effects.

Adult↗
PubMed1997

Use of reverse transcription-polymerase chain reaction methodology to detect estrogen-regulated gene expression in small breast cancer specimens.

We describe the development and use of a sensitive reverse transcription-PCR (RT-PCR) procedure to detect novel estrogen-regulated gene expression in small clinical breast cancer samples, in which such study would be extremely difficult by any other molecular or immunocytochemical means. Assay optimization for pLIV1, estrogen receptors (ERs), progesterone receptors, and pS2 gene products was carried out on 50 primary breast cancers for which comparative Northern analysis and immunocytochemical data were available. Using 27 amplification cycles and a 0.5 microM primer concentration, varying expressions of the gene products were recorded simultaneously with a constant densitometric signal for a coamplified endogenous control gene (alpha-actin). Good concordances were subsequently observed between pLIV1 status generated by RT-PCR and both Northern analysis (P = 0.002) and ER status by immunocytochemistry (P = 0.0244). Agreement was also noted between ER (P = 0.002), progesterone receptor (P = 0.0005), and pS2 (P = 0. 0023) RT-PCR and immunocytochemical methodologies. The RT-PCR assays were then applied to 10 needle core trucut biopsies in which similar relationships were obtained. Our results justify the future use of this RT-PCR methodology to examine new estrogen-regulated genes in small breast cancer samples, and it is envisaged that this technology will prove invaluable in many future breast cancer studies.

Biomarkers, Tumor↗
PubMed1996

Quantification of Spatial Correlation in Porous Media and Its Effect on Mercury Porosimetry.

In many porous media the grains are packed in a disordered manner, rather than in regular lattices. Theoretical treatments of the properties of these media often assume that because there is no regular lattice, the pore space between grains is completely spatially disordered. Here we present an analysis of a real granular medium (a close packing of equal spheres) which shows that, contrary to the popular assumption, the pore space is spatially correlated. The origin of this pore space correlation is the strong spatial correlation of grain locations, which is a feature of all dense granular media. Our analysis relies on physically representative network models of the pore space constructed from knowledge of the grain locations. Simulated drainage experiments on these networks agree with mercury porosimetry experiments in simple sandstones, whereas simulations in uncorrelated but otherwise identical networks do not. Thus the spatial correlation inherent in the pore space of simple porous media significantly affects mercury porosimetry. Deriving pore size distributions from mercury porosimetry without considering spatial correlation can give misleading results. The likelihood of error is compounded if such pore size distributions are used to estimate transport coefficients such as permeability, diffusivity, and electrical conductivity.

Journal Article↗
PubMed1996

The statistics of unique native states for random peptides.

Given a probability distribution from which the energy spectrum of a random peptide is to be sampled, we derive a general expression for the probability that such a peptide will fold to a unique native state and for the probability distribution of the native energy. This latter result allows us to localize the energy of folding based on model parameters and is one advantage of our formulation. Evidence from both the lattice theory of proteins and protein threading experiments suggest that the energy spectrum for the compact states of a peptide chain is Gaussian in form. For this reason we have derived from the more general framework the specific formulas that apply in the Gaussian case, where one requires only the number of states and the variance of the Gaussian distribution in order to apply the theory. This simplicity allows us to perform calculations that we compare with calculations previously made by others based on statistical thermodynamics. We find qualitative agreement, but a significant correction to prior estimates of folding probability derived from the Gaussian assumption is necessary.

Mathematical Computing↗
PubMed1996

The predictors of red cell transfusions in total hip arthroplasties.

BACKGROUND: Most blood crossmatched in a hospital blood bank is for surgical patients, and the majority is never transfused. The maximal standard blood order schedule is used to promote efficient ordering practices for surgical patients. STUDY DESIGN AND METHODS: To ascertain the predictors of red cell transfusions for patients undergoing total hip arthroplasty, the charts of 299 adult patients undergoing primary and revision total hip arthroplasty were reviewed. A surgical blood order equation was developed for calculating the number of units of red cells that should be ordered. Stepwise regression analysis was used to determine which patient-and-case-related variables should be considered in the surgical blood order equation. RESULTS: The significant indicators for allogeneic red cell transfusion to patients on the day of total hip arthroplasty were preoperative hemoglobin concentration, weight, age, estimated blood loss, and aspirin use. The surgical blood order equation would result in a lower crossmatch-to-transfusion ratio than would the maximal standard blood order schedule (1.23 vs. 3.14). Costs were also lower with the surgical blood order equation. CONCLUSION: Incorporation of patient factors resulted in increased efficiency of blood-ordering practices in total hip arthroplasty.

Adult↗
PubMed1996

Root-end cavity preparation using the MicroMega Sonic Retro-prep Tip. SEM analysis.

The objective of this laboratory study was to compare root-end cavities prepared with sonic Retro-prep tips in a MM1500 Sonic Air handpiece with those created by burs in a conventional handpiece. A total of 80 single-rooted extracted human teeth with mature apices and straight canals were included in the study. Four groups of 20 extracted teeth were prepared as follows: I, a 3-4 mm root-end resection perpendicular to the long axis of the root, with a size 40 sonic Retro-prep tip creating an apical cavity 3 mm into root canal system; II, a 45 degrees bevel of the root-face removing a 3-4 mm root segment and root-end preparation as per group I; III, root-end resection as per group I, with an apical cavity prepared using a size 010 inverted cone bur 3 mm down the long axis of the root; IV, resection as per group II, followed by an apical cavity preparation with a size 010 inverted cone bur 3 mm into the root canal system. The apical root portion and root-end cavities were replicated and prepared for SEM analysis at x 20 and x 80 magnification. The degree of chipping associated with the margin of the root-end cavities, as evaluated with a standard grading system, and the incidence of root-face cracks were noted. Marginal chipping of root-end cavities prepared using sonic instrumentation was significantly worse than that produced by burs (P < 0.001). Perpendicular root-end resections showed significantly better scores than bevelled root-end resections (P < 0.005). The incidence of root-face cracking was low with no significant difference between the experimental groups.

Dental Instruments↗
PubMed1995

The vav proto-oncogene is required early in embryogenesis but not for hematopoietic development in vitro.

Previous studies have suggested that the vav protooncogene plays an important role in hematopoiesis. To study this further, we have ablated the vav protooncogene by homologous recombination in embryonic stem (ES) cells. Homozygous vav (-/-) ES clones differentiate normally in culture and generate cells of erythroid, myeloid and mast cell lineages. Mice heterozygous for the targeted vav allele do not display any obvious abnormalities. However, homozygous embryos die very early during development. Crosses of vav (+/-) heterozygous mice yield apparently normal vav (-/-) E3.5 embryos but not post-implantation embryos (> or = E7.5). Furthermore, homozygous vav (-/-) blastocysts do not hatch in vitro. These results indicate that vav is essential for an early developmental step(s) that precedes the onset of hematopoiesis. Consistent with the phenotypic analysis of vav (-/-) embryos, we have identified Vav immunoreactivity in the extra-embryonic trophoblastic cell layer but not in the inner embryonic cell mass of E3.5 preimplantation embryos or in the egg cylinder of E6.5 and E7.5 post-implantation embryos. These results suggest that the vav gene is essential for normal trophoblast development and for implantation of the developing embryo.

Animals↗
PubMed1995

Differential expression of oestrogen regulated genes in breast cancer.

Pathological endpoints such as tumour size, lymph node status and vascular invasion remain the most useful guides in selecting treatment strategies for breast cancer. There is a need, however, to further investigate the molecular mechanisms that determine the properties of an individual tumour e.g., hormone responsiveness and probability of metastasis. While numerous prognostic factors have now been identified few have contributed to defining clinical response to therapy. Oestrogen-regulated genes are likely to be important since they not only define a functional oestrogen receptor, but alterations in their expression might provide insights into the mechanisms involved in tumour progression and loss of endocrine sensitivity. Recently an oestrogen responsive gene, pLIV1, has been isolated and shown to be expressed in ER+ disease where it appears to predict nodal involvement. The present paper describes aspects of its regulation and discusses the potential role of this and other genes in the development of endocrine resistance.

Breast Neoplasms↗
PubMed1995

MMDB: an ASN.1 specification for macromolecular structure.

We present an exchange specification for data describing the three-dimensional structure of biological macromolecules. The specification was designed for MMDB, a Molecular Modeling Database supported by the National Center for Biotechnology Information (NCBI), based on information from the Protein Data Bank (PDB). In the MMDB specification, the chemical structures of molecules are described hierarchically as connectivity graphs, to directly support comparison by subgraph isomorphism or assignment algorithms. Three-dimensional coordinates are linked unambiguously to nodes in the chemical graph, so that homology-derived structures may be generated directly from alignment of chemically similar groups. In conversion to this form, data from PDB are extensively validated, so as to provide a description of chemical and spatial structure that is as accurate as possible. These changes in format and content of the known structure data are intended to support development of intelligent molecular modeling applications that make use of this invaluable information resource.

Amino Acid Sequence↗
PubMed1994

Severe sensory and sympathetic neuropathies in mice carrying a disrupted Trk/NGF receptor gene.

Nerve growth factor (NGF) induces neurite outgrowth and promotes survival of embryonic sensory and sympathetic neurons in culture. In vivo, NGF decreases the extent of naturally occurring cell death in developing sympathetic ganglia and protects cholinergic neurons of the basal forebrain and caudatoputamen. NGF interacts with the low-affinity p75 receptor and with Trk, a receptor tyrosine kinase encoded by the trk proto-oncogene. To study the role of Trk in vivo, we have ablated the gene in embryonic stem cells by homologous recombination. Mice lacking Trk have severe sensory and sympathetic neuropathies and most die within one month of birth. They have extensive neuronal cell loss in trigeminal, sympathetic and dorsal root ganglia, as well as a decrease in the cholinergic basal forebrain projections to the hippocampus and cortex. These findings demonstrate that Trk is the primary mediator of the trophic actions of NGF in vivo and that this signalling pathway plays a crucial role in the development of both the peripheral and the central nervous systems.

Acetylcholinesterase↗
PubMed1994

Disruption of the neurotrophin-3 receptor gene trkC eliminates la muscle afferents and results in abnormal movements.

The trkC gene is expressed throughout the mammalian nervous system and encodes a series of tyrosine protein kinase isoforms that serve as receptors for neurotrophin-3 (NT3), a member of the nerve growth factor (NGF) family of neurotrophic factors. One of these isoforms, gp145trkC/TrkC K1, mediates the trophic properties of NT3 in cultured cells. Here we show that homozygous mice defective for TrkC tyrosine protein kinase receptors lack Ia muscle afferent projections to spinal motor neurons and have fewer large myelinated axons in the dorsal root and posterior columns of the spinal cord. These mice display abnormal movements and postures, indicating that NT3/TrkC-dependent sensor; neurons may play a primary role in proprioception, the sense of position and movement of the limbs.

Amino Acid Sequence↗
PubMed1992

Identification of candidate sequences that determine virulence in Coxsackievirus B4.

We have previously shown that a major determinant of virulence for coxsackievirus B4 mapped to the 5' end of the viral genome. Comparison of the corresponding cDNA sequences of a virulent and a non-virulent virus has allowed the identification of candidate determinants of virulence in the 5' untranslated region and the capsid proteins VP1, VP2 and VP4. Thirteen nucleotide substitutions were observed in a region spanning 3298 nucleotides. Four mutations were detected in the non-coding region. Of the remaining nine mutations, four were silent while five resulted in amino acid substitutions in VP1, VP2 and VP4. The amino acid substitutions in the virulent virus were analyzed in relation to the three-dimensional structures of the capsid proteins of poliovirus. Two substitutions mapped to the amino termini of VP1 and VP4. Of the two substitutions observed in VP2, one mapped to the large loop that connects beta strand E with the radial helix on the back surface of the eight-stranded antiparallel beta barrel while the other mapped to beta strand G. One amino acid substitution in VP1 mapped to the loop connecting beta strands D and E at a site close to a major determinant of attenuation in poliovirus type 2.

Amino Acid Sequence↗
PubMed1992

The trkB tyrosine protein kinase is a receptor for neurotrophin-4.

Neurotrophin-4 is a novel member of the nerve growth factor family of neurotrophins recently isolated from Xenopus and viper DNA. We now report that the Xenopus NT-4 protein (XNT-4) can mediate some of its biological properties through gp145trkB, a murine tyrosine protein kinase previously identified as a primary receptor for the related brain-derived neurotrophic factor (BDNF). XNT-4 displaces 125I-labeled BDNF from binding to cells expressing gp145trkB receptors, induces their rapid phosphorylation on tyrosine residues, and causes the morphologic transformation of NIH 3T3 cells when coexpressed with gp145trkB. Moreover, XNT-4 induces the differentiation of PC12 cells into sympathetic-like neurons only if they ectopically express gp145trkB receptors. None of these biochemical or biological effects could be observed when XNT-4 was added to cells expressing the related receptors. Replacement of one of the extracellular cysteines (Cys-345) of gp145trkB by a serine residue prevents its activation by XNT-4 but not by BDNF. Therefore, XNT-4 and BDNF may interact with at least partially distinct domains within the gp145trkB receptor.

Adrenal Gland Neoplasms↗
PubMed1992

Molecular genetics of the human cytochrome P450-dependent monooxygenases.

In this work, the role of genetic as well as environmental factors in determining cytochrome P450 isozyme levels in man have been studied. Simple DNA based assays for the identification of individuals nulled at the CYP2D6 locus are described and have been applied to investigate whether this gene defect is associated with altered cancer susceptibility. In contrast to literature reports, in no cancer type were poor metabolizers underrepresented, indeed in several cancers the mutant allele frequency was increased. A model using human tumours grown as xenografts is described that should help elucidate the factors which regulate P450 levels in man.

Chromosome Mapping↗