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Biomedical subjects

D Smith

Publications and source records attributed to D Smith.

At least 649 records · Page 36Linked to original sources
PubMed1994

Penetration of a dentin bonding agent into dentin.

PURPOSE: To examine how the priming agents of Scotchbond Multi-Purpose (SMP) influenced the wettability of collagen in the demineralized zone and hence the penetration and adaptation of its bonding monomers. MATERIALS AND METHODS: Freshly extracted bovine teeth were ground to dentin with SiC paper. SMP and Z100 resin were used. Shear bond testing was performed as well as scanning electron microscopic evaluation. RESULTS: In contrast to the manufacturer's instructions, a 26.3% increase in shear bond strength was obtained when a second coat of priming agent was applied. This increase was statistically significant at the 5% level of confidence. SEM examination of failed conventionally air dried (CAD) specimens showed the presence of voids in the demineralized layer. SEM examination of failed specimens prepared by a critical point drying (CPD) technique showed that these voids were filled with collagen fibrils. The CPD technique also clearly showed that collagen fibrils were incorporated in the unfilled resin. Although priming agents appear to facilitate the penetration of unfilled resin into the demineralized layer and the dentin tubules, areas of unincorporated collagen fibrils can be seen even after two or more applications of the priming agent.

Analysis of Variance↗
PubMed1994

Financing health services for children in Texas.

In Texas, children's health services are financed by a bewildering combination of private and public sources, each of which employs different eligibility rules, benefit packages, and reimbursement methods. This article describes these financing mechanisms, underscoring their complexity and the need for consolidation and reform. As private coverage for children has declined, it has become less comprehensive with increased coinsurance and deductibles. Concurrently, due to a number of federal initiatives, Medicaid coverage has increased rapidly with new benefits, also now mandated. Levels and structure of payment have influenced variable participation in the program by physicians, rural health clinics, federally qualified health centers, and children's hospitals. The Texas Department of Health and the Texas Department of Mental Health and Mental Retardation have undertaken a number of initiatives to fill in the gaps and to serve mandated categorically eligible populations. Continuity of care is difficult to achieve. Comprehensive community-based care should be promoted with the goal of expanding the role of all types of providers.

Adolescent↗
PubMed1994

African-American adults' perceptions of guns and violence.

This study examined African-American adults' perceptions of guns and violence. Through a mall intercept type study, 347 adults, ages 20 to 75, responded to a 54-item questionnaire. One third of the respondents claimed they owned one or more types of guns, three fourths had personally known someone who had been shot, more than one third had actually seen someone shot, and one third had a gun pulled on them. While the vast majority (84%) believed guns are too easy to obtain, the majority (62%) also believed that having a gun at home would help protect them. There were no significant differences in perceptions of guns based on age, gender, level of education, or socioeconomic status. The results of this study tend to substantiate the concern and fear of personal harm that African Americans have to contend with on a regular basis. The results also suggest the need for some form of educational intervention and gun safety training in order to help reduce the risk of death and injury among African Americans.

Adult↗
PubMed1994

Wear induced by motion between bone and titanium or cobalt-chrome alloys.

We studied the wear generated by motion between polished and shot-blasted titanium-alloy (Ti-6Al-4V) or cobalt-chrome alloy (Co-Cr) surfaces and cortical bone in vitro. Semicircular sections of human proximal femoral cortex were reamed to fit metal cylinders of each alloy. The cylinders were then fitted in the bone, loaded and rotated in physiological saline. Ti-alloy resulted in more wear both of the bone and of the metal than did Co-Cr alloy. Metal wear was reduced and bone wear was increased by shot-blasting, a procedure which introduces surface residual stresses and roughens the metal surface. We conclude that when there is gross motion between a metal implant and bone, Ti-alloy is likely to generate more wear debris than Co-Cr alloy. The least wear both of bone and of metal was produced by polished Co-Cr.

Bone Density↗
PubMed1994

Endocrine consequences of weight loss in obese, hyperandrogenic, anovulatory women.

OBJECTIVE: To determine whether weight loss in obese, hyperandrogenic, anovulatory women is associated with resumption of ovulation and/or with changes in insulin, androgen, and gonadotropin concentrations. DESIGN: Prospective, randomized, controlled study. SETTING: University research center. PATIENTS: Twelve obese, hyperandrogenic, anovulatory women. INTERVENTIONS: Twelve-week weight loss program in treatment (n = 6); 12-week "waiting list" in control group (n = 6). MAIN OUTCOME MEASURES: [1] Ovulation; [2] fasting insulin and glucose measurements; [3] sex hormone-binding globulin (SHBG), total and non-SHBG T concentrations; [4] LH pulse frequency, amplitude, and concentration; and [5] FSH concentration. RESULTS: In contrast with the control group who showed no change in weight, ovulation status, or hormone levels, women in the treatment group lost an average of 16.2 kg and showed a significant increase in SHBG, a significant decline in non-SHBG T, and a decline (though nonsignificant) in fasting insulin. Four of six subjects resumed ovulation. However, no changes were evident in LH pulse frequency or amplitude or in mean LH and FSH concentrations. CONCLUSIONS: Weight loss in obese, hyperandrogenic, anovulatory women appears to reduce insulin and non-SHBG T concentrations despite the absence of a change in gonadotropin secretion and may lead to resumption of ovulation.

Adult↗
PubMed1994

The morphology of the demineralized layer in primed dentin.

This study critically examined the surface and subsurface effects of selected dentin priming agents. Various dentin priming agents were used and specimens were prepared for SEM examination by conventional air drying or by a freeze fracture and critical point drying technique. The results showed that in specimens prepared by freeze fracture and critical point drying technique the demineralization of the dentin surface and subsurface by priming agents leaves a visible network of collagen fibrils. This technique allows better evaluation of the adaptation of bonding resins to the collagen network of the demineralized layer.

Acid Etching, Dental↗
PubMed1993

Cloning and sequence of a chicken alpha-N-acetylgalactosaminidase gene.

A cDNA clone encoding the mature polypeptide for the chicken liver alpha-N-acetylgalactosaminidase enzyme was isolated by screening a cDNA library with a synthetic sequence derived from the human alpha-N-acetylgalactosaminidase gene. The deduced amino acid sequence of the chicken liver clone was identical to the amino-terminal and cyanogen bromide derived peptide sequences obtained from the purified enzyme. The chicken enzyme has 75% identity with the human alpha-N-acetylgalactosaminidase and 56-33% identity with alpha-galactosidases from several sources.

Amino Acid Sequence↗
PubMed1993

Autoradiographical evaluation of [3H]glycine uptake in rat forebrain: cellular localization in the hippocampus.

The cellular elements responsible for the uptake of [3H]glycine into rat hippocampal slices were investigated. The diffuse laminar distribution of labelling observed under control conditions was greatly reduced seven days after intrahippocampal injection of a neurotoxic dose of quinolinic acid, suggesting a neuronal localization. Glycine was also taken up into glial cells, since dense clusters of silver grains were present on small sized cells throughout the hippocampus which were apparently increased in number after the lesion. The pattern of [3H]glycine uptake into rat cerebral cortex and cerebellar slices was also consistent with both neuronal and glial localization. These glycine transport sites may be strategically located to control excitatory neurotransmission mediated by the N-methyl-D-aspartate sub-type of glutamate receptors.

Animals↗
PubMed1993

The role of alpha-tocopherol as a peroxyl radical scavenger in human low density lipoprotein.

It is thought that the oxidation of low density lipoprotein (LDL) plays a key role in the pathogenesis of atherosclerosis. It is well known that lipid peroxidation reactions are propagated by peroxyl radicals and it follows, therefore, that the capacity of an individual LDL particle to scavenge these oxidants may be an important indicator of its atherogenic potential. There are several components within LDL which scavenge peroxyl radicals including chain breaking antioxidants and amino acids on the protein. It is not clear at present which of these antioxidants is most important. In attempting to address the question we have used a simple method for the measurement of the total capacity of the LDL particle to scavenge peroxyl radicals. This assay depends upon the ability of antioxidants in LDL to inhibit the peroxyl radical dependent oxidation of luminol. We have found that approximately 80% of the antioxidant capacity of LDL, isolated from a number of donors, could be accounted for by the alpha-tocopherol present in the samples. We have compared these results with those obtained when the identical samples of LDL were oxidized with copper and found, as reported by others, a wide range in the susceptibility of the different LDL preparations to oxidation by this transition metal. We suggest that this variability is unlikely to be due to differences in the ability of an LDL particle to scavenge peroxyl radicals.

Adult↗
PubMed1993

Multiple magnesium ions in the ribonuclease P reaction mechanism.

The ribozyme ribonuclease (RNase) P cleaves precursor transcripts to produce the mature 5'-end of tRNAs. This hydrolysis reaction has a divalent cation requirement that is primarily catalytic, rather than structural; RNase P can be considered a metalloenzyme. Kinetic analysis shows that the RNase P catalytic mechanism has a cooperative dependence upon Mg2+ concentration. At least three Mg2+ ions are required for optimal activity, suggesting a multiple metal ion mechanism. The 2'-OH at the site of substrate cleavage may act as a ligand for a catalytically important Mg2+: deoxyribose substitution reduces the apparent number of Mg2+ bound from three to two and increases the apparent dissociation constant for Mg2+ from the micromolar to the millimolar range. In addition to these cation effects, the deoxyribose substitution reduces the rate of catalysis by 3400-fold; substitution with 2'-O-methyl at the cleavage site reduces the catalytic rate 10(6)-fold. If we presume no significant conformational effects of the substitutions, these results suggest that the 2'-OH serves as hydrogen-bond donor. The kinetic analysis of the catalytic mechanism is based upon the characterization of the pH dependence of the reaction. There is a hyperbolic (saturable) dependence on hydroxide concentration, with the half-maximal rate achieved at pH 8.0-8.5. The rate of the cleavage step is about 200 min-1 at pH 8.0, which is 500-fold faster than the steady-state parameter kcat.

Calcium↗
PubMed1993

Effect of stress management on blood pressure in mild primary hypertension.

OBJECTIVE: To establish whether stress management had a larger effect than a control treatment on resting blood pressure, ambulatory blood pressure, and left ventricular mass. DESIGN: A 12 week baseline period of habituation to measurement of blood pressure was followed by randomisation to either stress management or mild exercise for six months and follow up six months later. SETTING: General practice, district general hospital, and medical school. PATIENTS: Of the 184 patients aged under 60 with mild primary hypertension who entered the baseline habituation period, 88 were excluded because they failed to meet the entry criteria or they withdrew from the study. The remaining 46 men and 50 women underwent treatment. INTERVENTIONS: 10 clinical sessions and daily practice at home of either stress management based on relaxation or non-aerobic stretching exercises. Mildly stressful 15 minute interviews before and after treatment. MAIN OUTCOME MEASURES: Diastolic and systolic blood pressure in the clinic and during 12 hours of ambulatory recording, and left ventricular mass measured by echocardiography. RESULTS: The patients' blood pressure fell during habituation (systolic pressure from 152 mmHg to 140 mmHg, diastolic pressure from 98 to 93 mm Hg), but neither resting nor ambulatory blood pressure was changed by the treatments. Left ventricular mass was also unchanged. Blood pressure rose during the stressful interview, but this rise was reduced by stress management (systolic pressure rose by 7.4 mmHg before treatment and by 3.7 mmHg after treatment). CONCLUSION: Stress management of a type advocated for treating mild primary hypertension is ineffective in lowering blood pressure in patients who are well habituated to measuring blood pressure.

Adult↗
PubMed1993

An ELISA for blood group specific exoglycosidases.

An enzyme-linked immunosorbent assay (ELISA) for studying erythrocyte A, B and H epitope specific exoglycosidases is described. Human blood type B erythrocyte membranes and Coffea canephora alpha-D-galactosidase were used as a model. Membrane coated microtiter wells were incubated with exoglycosidase, probed with IgM monoclonal antibody, and then with anti-murine mu chain specific alkaline phosphatase conjugate. The assay is useful for studying exoglycosidase modification of the A, B and H epitopes on human erythrocyte membranes as well as in screening prokaryotic and eukaryotic extracts for blood group active enzymes. Furthermore, this technique has the advantage of simplicity, sensitivity, and objectivity of data interpretation.

Blood Group Antigens↗