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Biomedical subjects

G C Levy

Publications and source records attributed to G C Levy.

At least 19 recordsLinked to original sources
PubMed1995

Effects of Nd:YAG laser on the permeability of root canal wall dentin.

The effects of a thermally cooled pulsed Nd:YAG laser on the permeability and structural appearance of the root canal wall were investigated in vitro. Twenty specimens of freshly extracted human teeth were prepared by conventional methods. The teeth were randomly divided into two groups. Group 1 teeth were prepared conventionally but not lased. Group 2 specimens received three 15-s laser exposures totaling 45 s duration within the root canal via optical fiber delivery. Laser parameters were set at 5 W, 50 Hz, using a simultaneous air/water coolant spray of 10 psi air and 2 psi water. The external surfaces of the teeth were sealed with acrylic and placed in 2% methylene blue dye for 24 h. The teeth were then sectioned, photographed, and compared under light microscope for the extent of dye penetration. The specimens were subsequently prepared for scanning electron microscopy for correlation of permeability measurements with surface modifications. The combined use of scanning electron microscopy and dye permeability measurements revealed a sealing of the dentinal wall by deposition of glass-like material and, in one specimen, the bridging of a lateral canal that partially occluded the canal. Based on statistical comparisons, permeability of laser-treated teeth was significantly less than untreated specimens (alpha = 0.005).

Dental Pulp Cavity↗
PubMed1994

13C-NMR relaxation in three DNA oligonucleotide duplexes: model-free analysis of internal and overall motion.

Natural-abundance 13C-NMR spectra of [d(TCGCG)] (1), [d(CGCGCG)]2 (2), and [d(GGTATACC)]2 (3) were measured at 90.6 MHz to obtain 13C-1H NOEs and T1 relaxation times; relaxation data were also measured at 125.7 MHz for 1 and 2 and at 62.9 MHz for 1. Analysis of the relaxation data was performed in the context of the "model-free" approach of Lipari and Szabo [Lipari, G., & Szabo, A. (1982) J. Am. Chem. Soc. 104, 4546-4559], leading to the following conclusions: (i) Optimized values for the overall correlation times of 0.9 ns for 1 and 1.4 ns for 2 are close to those predicted by light-scattering results on similar molecules [Eimer et al. (1990) Biochemistry 29, 799-811]. (ii) For the nonterminal residues, the "order parameter", S2, is around 0.8 for the protonated base carbons and 0.6 for the sugar carbons, indicating less spatial restriction on the sugar carbons (in the model-free approach, the order parameter is 1 for a rigid body and 0 for a system with completely unrestricted internal motion). (iii) The order parameters for the terminal residues vary over a wide range with the smallest values around 0.2-0.3 for the HO-13C5' and the 13C3'-OH; rational trends are seen in the variation of S2 with chain position in the terminal residues. (iv) The analysis shows that the order parameters are accurate within 15%. (v) The "effective internal correlation time", tau e, is very short for the sugar carbons (30-300 ps) and less well-defined, but probably also short, for the bases. (vi) The analysis indicates that most of the relaxation in DNA is accounted for by S2 and the tau e is so short that a good approximation to any relaxation property, P (e.g., T1, T2, 13C-1H NOE, 1H-1H cross-relaxation rate), is P = S2Prigid, where Prigid is the value for the property in a system without internal motion (the analysis assumes the same isotropic overall motion for both the rigid and flexible bodies).

Base Sequence↗
PubMed1994

Histologic effects of a thermally cooled Nd: YAG laser on the dental pulp and supporting structures of rabbit teeth.

The histologic response of the pulp, periapical tissues, supporting periodontal ligament, and alveolar bone adjacent to the incisor teeth of adult rabbits was compared after laser treatment (etching) or drilling with a high-speed dental rotary handpiece (enamelplasty) on the buccal enamel surface. Observations were made at four time periods, 2 days, 14 days, 60 days, and 180 days after treatment. Block sections were removed, and serial sections were prepared and examined by an independent veterinary pathologist for occurrences of histopathologic changes with untreated control teeth used for comparison. Under the conditions of this study, there were no differences between either the laser-treated or the drilled specimens compared with the untreated control teeth on the basis of the histologic appearance.

Animals↗
PubMed1994

The efficiency of bone ablation with an Nd:YAG laser beam delivered with a cooling spray: an in vitro study.

This investigation studied the ablation of cortical bone with a neodymium:yttrium-aluminium-garnet (Nd:YAG) laser and how an air and water cooling spray effectively reduced the amount of heat transferred to the surrounding tissue. A 600-microns-diameter optical fiber and a 400-microns-diameter optical fiber were used to deliver an Nd:YAG laser beam to the cortical bone of two rabbit tibiae while a continuous air and water cooling spray provided cooling and irrigation to the tissue site. Different power settings and energy densities were used on 6 groups of 10 holes each. The holes were then prepared for scanning electron microscope examination and average and standard deviations were calculated for each group of collected data. The results showed that the Nd:YAG pulsed laser beam with an experimental cooling irrigation system ablated bone efficiently with minimal thermal damage.

Animals↗
PubMed1993

A comparison of dentin permeability after bur and laser apicoectomies.

This investigation compared the permeability of dentinal tubules after laser beam and conventional bur apicoectomies. Twenty roots were rountinely instrumented and obturated with laterally condensed gutta-percha. A bur was used to cut the apexes of 10 teeth, while the remaining 10 were cut with a laser beam carried through an optic fiber. A 35-W pulsed Nd:YAG laser system capable of cooling the irradiated area with an air and water spray supplied the power. Except for the apex, the teeth surfaces were coated with a blue wax. The samples were stored for 36 hours in a 2.5% methylene blue solution and were washed, split, and measured for dye penetration. Linear penetration in series 1 averaged 2.4 mm, while series 2 measured 0.9 mm. The laser apicoectomy appears to reduce the permeability of dentinal tubules.

Apicoectomy↗
PubMed1993

An experimental technique to repair cracked teeth using calcium phosphate, melted by a laser beam: an in vitro evaluation.

Using a neodymium: yttrium-aluminum-garnet laser beam to seal vertical root fracture lines with tricalcium phosphate paste represents an alternative treatment for cracked teeth with noted clinical results. This article describes a study of the permeability of molten crystals of hydroxyapatite in the dentin of a cracked root after crack lines have been filled with a preparation of tricalcium phosphate melted by a neodymium: yttrium-aluminum-garnet laser beam. The morphology of the sealed cracks was analyzed under a scanning electron microscope that showed a deep fusion of tricalcium phosphate along crack lines.

Calcium Phosphates↗
PubMed1991

An evaluation of new processing protocols for in vivo NMR spectroscopy.

In vivo NMR spectroscopy is often complicated with problems of low signal-to-noise, poor resolution, undefined peak shapes, and nonlinear baselines despite the efforts of investigators to optimize their experiments. Several data processing options are available to spectroscopists to enhance resolution and signal-to-noise and/or to flatten baselines. There is some question about how these processing protocols affect quantitative information. This paper evaluates five different processing protocols for their ability to extract quantitative information from a set of nonideal spectra. Three of the protocols involve recently developed statistical signal processing methods, maximum entropy Fourier spectral deconvolution, linear prediction singular value decomposition, and baseline deconvolution. These protocols are compared with the conventional processing methods of convolution difference and zeroing initial data points of the FID. The methods are evaluated by use of a quantitative 31P model sample and also are demonstrated on surface coil 31P data.

2,3-Diphosphoglycerate↗
PubMed1989

Characterization of normal brain tissue using seven calculated MRI parameters and a statistical analysis system.

A statistical analysis system for classifying normal brain tissue has been applied to the analysis of MRI scans on 45 volunteers. The Bayes Maximum Likelihood method was used to achieve a discrimination accuracy of 84% for 13 tissue types among three age group sets, with classification accuracies for individual regions ranging from 50 to 100%. In order to attain this level of discrimination a set of seven derived relaxation-type parameters was used to categorize the tissue types. Values for these experimentally estimated parameters were derived from the MRI intensities of eight images in the following pulse sequences: (1) a Carr-Purcell-Meiboom-Gill (CPMG) four-echo train, (2) a single-echo inversion recovery, and (3) three single-echo sequences with varying repetition times, TR, and echo delays, TE. The T2 values derived from ratios of single-echo intensities showed better discrimination power than those from the four-echo CPMG train. The general precision of the seven estimated parameters was excellent, with percentage standard deviations ranging from 4 to 18% for the various regions studied. The tissue discrimination achieved by use of just three relaxation parameters, T1, T2, and proton density, calculated from intensities of images from a four-echo sequence, an inversion recovery sequence, and a short TR single-echo sequence, was not as good, being only 55%.

Adult↗
PubMed1988

13C NMR of the bases of three DNA oligonucleotide duplexes: assignment methods and structural features.

Natural abundance 13C NMR spectra of three DNA oligomers have been obtained. Most of the base resonances are well resolved from one another. A combination of two independent methods was used in making assignments: a one-dimensional spectral comparison method and a two-dimensional proton-detected 1H-13C correlated experiment for the protonated carbons. There are large shielding changes (between 1.62 and -1.40 ppm) upon thermal dissociation of the duplex. The shapes of the chemical shift vs temperature curves are largely independent of sequence. The base carbon resonance frequencies are sensitive to hydrogen bonding, base stacking, sugar conformation, and changes in the glycosyl torsion angle.

Base Composition↗
PubMed1988

Hydrogen-bonding effects and 13C-NMR of the DNA double helix.

13C-nmr chemical shifts of the nucleotides in DNA are sensitive to hydrogen bonding, especially for three of the carbons immediately bonded to exocyclic oxygen or nitrogen atoms acting as H-bond acceptors or donors. GuoC2, GuoC6 and ThdC4 are strongly deshielded (about 1 ppm) upon Watson-Crick pairing in oligodeoxynucleotide duplexes, regardless of the base sequence. Deshielding at these sites may be useful to distinguish bases involved in Watson-Crick pairs from unpaired bases.

Chemical Phenomena↗
PubMed1988

How changes in computer technology are revolutionizing the practice of chemistry.

During the early 1980s, two major developments in computer technology changed the way chemists approached their science. The advent of the micropressor and then the PC changed experimental chemistry, while the availability of two classes of computer, the superminicomputer and supercomputer, greatly influenced computational chemistry. In the past two years, graphics workstation computers have begun to affect the practice of chemistry by combining fast, high-resolution, multiwindow graphics with superminicomputer power. In 1988, the advent of a new class of computer--the graphics supercomputer--offers extraordinary promise to both theoretician and experimentalist. In these systems, near-Cray compute power is combined with ultrahigh-speed 3-dimensional graphics for unparalleled visualization of molecular processes and other complex events. This is made practical not just by computing and graphics power but by use of ultrahigh internal bandwidths inside the graphics supercomputers. Another major development in scientific computing is the evolving concept of the laboratory computer network. Current network designs include hierarchical configurations incorporating various levels of computers--through supercomputers--either locally or via national or regional networks. New software methods are also having impact on chemical research, allowing, for example, the scientist to better abstract information from noisy or incomplete experimental data. Use of parallelism (multiple CPUs) in new design workstation computers will extend their power, by the early 1990s, past that of current supercomputer mainframes. Within five years the chemist will have $10 million of 1985 computer power on his desk, for considerably less than $100,000, along with visualization tools and software only dreamed of in 1985.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗
PubMed1988

13C NMR assignments of the bases in oligodeoxynucleotides: an automated procedure using Bayesian statistics.

A statistical method, Bayes Maximum Likelihood, has been applied to the classification of base 13C NMR resonances in DNA oligomers. An accuracy of 100% for carbon class discrimination was achieved for a preliminary training set of four oligomers using the following four parameters: (1) the chemical shift; (2) the temperature at which the spectrum was obtained; (3) the difference in chemical shift from the C5 resonances; and (4) a sequence factor representing the neighboring nucleotides. Classification of a fifth oligomer, previously assigned and not contained in the original training set, gave reasonable carbon class assignments.

Base Sequence↗
PubMed1988

13C NMR assignments of the protonated carbons of [d(TAGCGCTA)]2 by two-dimensional proton-detected heteronuclear correlation.

The resonances of the protonated carbons of [d(TAGCGCTA)]2 have been assigned by the two-dimensional proton-detected double-quantum heteronuclear correlation experiment [( 1H-13C]-DQCOSY). 13C-coupled and 13C-decoupled versions of the experiment were used. The assignment method is discussed in detail. The deoxyribose cross peaks segregate into five well-resolved regions, and the base cross peaks have distinct features that are helpful for assignments. The cross peaks from the 1H-13C pairs at the Cyd5, Ado2 and ThdCH3 base positions fall in separate regions of the spectrum from each other; they also are resolved from the closely spaced Ado8, Guo8, Cyd6 and Thd6. Additional parameters for distinction of the base signals are their differing J-coupling values and long-range coupling patterns.

Carbon Isotopes↗
PubMed1987

A transfer nuclear Overhauser effect study of coenzyme binding to distinct sites in binary and ternary complexes in glutamate dehydrogenase.

The oxidized coenzyme NAD binds to two sites per subunit of bovine liver glutamate dehydrogenase with equal affinity in the absence of dicarboxylic acid coligands. In the presence of glutarate or 2-oxoglutarate, the affinity to one site is unchanged, but the affinity to the other (presumed to be the active site) is considerably increased and now requires two dissociation constants to describe its saturation. A combination of transfer nuclear Overhauser effects (TRNOE) together with an examination of the slopes of TRNOE time dependence indicates that while NAD is bound in a syn conformation at both binding sites, NADP (which binds only to the active site) is bound in a syn-anti mixture. The existence of N6 to N3' and N6 and N2' and N1' to N3' NOE's with NAD suggests that the two coenzyme binding sites are located near enough to allow intermolecular NOE's. In the presence of 2-oxoglutarate where only binding to the active site is effectively observed, the conformation of either coenzyme is syn. Modeling studies using the distance estimates from the TRNOE results suggest that the nicotinamide ribose approximates a 3'-endo conformation. The absence of evidence for intermolecular NOE's under these conditions indicates that while the active and regulatory NAD sites per subunit are in close proximity, the six active sites per hexamer are located greater than 5 A apart.

Animals↗
PubMed1987

Effects of ethanol on gastric epithelial cell phospholipid dynamics and cellular function.

The lipid profile of isolated gastric superficial epithelial cells (SEC) was evaluated by proton nuclear magnetic resonance spectroscopy (1H-NMR). The most conspicuous resonance band in SEC spectra was due to the protons of +N(CH3)3 groups of phosphatidylcholine and, to a lesser degree, other phospholipid derivatives, on the basis of their chemical shift and addition of purified phospholipids. NMR of cell lysates and phospholipid extracts of SEC in deutero-chloroform provided further spectral resolution of these components. Phospholipase or ethanol treatments of SEC produced membrane disorganization reflected as increased peak intensity of the phospholipid signals. In addition, ethanol, in a dose-dependent manner, attenuated paranitrophenyl phosphatase activity, which correlated with inhibition of total and ouabain-sensitive 86Rubidium chloride uptake by SEC. This study suggests that NMR used in conjunction with other biochemical techniques can monitor SEC membrane structure-function relationships. NMR is a potentially powerful noninvasive probe to show changes in lipid membrane organization induced by low concentrations of ethanol (1%) and may indicate an early sign of "cytotoxicity" in intact SEC.

4-Nitrophenylphosphatase↗
PubMed1986

NMR studies of pig gastric microsomal H+,K+-ATPase and phospholipid dynamics. Effects of ethanol perturbation.

The effects of ethanol on the gastric H+,K+-ATPase activity and the degree of mobility of various microsomal phospholipids were assessed using 31P and 1H NMR. This illuminated the role of lipid-protein association in the function of pig gastric microsomes. Treatment of gastric microsomes with 15% ethanol for 1 min at 37 degrees C inactivated the H+,K+-ATPase activity, which could largely be reconstituted by supplementation with phosphatidylcholine isolated from the gastric microsomes. Under similar conditions, the 1H NMR profile of the microsomal +N(CH3)3 choline moiety showed dramatic enhancement of peak intensity as well as a break point at 25 degrees C which was restored to the untreated control value after reconstitution. This break, together with the dramatic enhancement in the overall lipid profile, compared to the control and reconstituted microsomes, suggested a greater degree of freedom of movement of the microsomal lipids following ethanol perturbation. The data demonstrate the unique ability that a combined approach using 31P and 1H NMR holds as a noninvasive probe to study the structure-function relationship of biomembranes.

Adenosine Triphosphatases↗