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Biomedical subjects

B Dickens

Publications and source records attributed to B Dickens.

11 recordsLinked to original sources
PubMed1999

Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators.

To examine the site of action of antimalarial iron chelators, iron ligands were added to control erythrocytes and to erythrocytes parasitized with Plasmodium falciparum, and the concentration of intracellular labile iron was monitored with the fluorescent probe, calcein. The fluorescence of calcein quenches upon binding iron and increases upon releasing iron. The chelators included desferrioxamine B, 2',2'-bipyridyl, and aminophenol II, a compound that is being newly reported as having anti-plasmodial properties. Calcein-loaded parasitized cells displayed fluorescence predominantly within the cytosol of both rings and trophozoites. The addition of chelators to both control and parasitized erythrocytes led to significant increases of fluorescence (P < 0.001). Fluorescence was observed to increase within the parasite itself after addition of iron chelators, indicating that these agents bound labile iron within the plasmodium. The relative increases of fluorescence after addition of chelators were greater in control than parasitized erythrocytes (P < 0.05) as were the estimated labile iron concentrations (P < or = 0.001). These results suggest that (i) the anti-malarial action of iron chelators might result from the ability to reach the infected cell's parasite compartment and bind iron within the parasite cytosol, and (ii) the labile iron pool of the host red cell may be either utilized or stored during plasmodial growth.

2,2'-Dipyridyl↗
PubMed1997

Bioethics for clinicians: 10. Research ethics.

Medical research involving human subjects raises complex ethical, legal and social issues. Investigators sometimes find that their obligations with respect to a research project come into conflict with their obligations to individual patients. The ethical conduct of research rests on 3 guiding principles: respect for persons, beneficience, and justice. Respect for persons underlies the duty to obtain informed consent from study participants. Beneficence demands a favourable balance between the potential benefits and harms of participation. Justice requires that vulnerable people not be exploited and that eligible candidates who may benefit from participation not be excluded without good cause. Studies must be designed in a way that ensures the validity of findings and must address questions of sufficient importance to justify the risks of participation. In any clinical trial there must be genuine uncertainty as to which treatment arm offers the most benefit, and placebo controls should not be used if effective standard therapies exist. Researchers have a responsibility to inform themselves about the ethical, legal and policy standards that govern their activities. When difficulties arise, they should consult the existing literature and seek the advice of experts in research ethics.

Beneficence↗
PubMed1995

Preparation and characterization of cyclopolymerizable resin formulations.

An amine-catalyzed reaction between acrylates and formaldehyde has been used to convert mono-acrylates to difunctional monomers and di-acrylates to multifunctional oligomers by linking the acrylic double bonds together in 1,6-diene pairs. The resulting monomers and oligomers undergo efficient cyclopolymerization to high conversion with significantly less shrinkage than normally found for acrylates. In this study, a convenient single-step process was used with mixtures of mono- and di-acrylate starting materials to produce a series of resins with potential for effective cyclopolymerization. Incremental changes in the ethyl acrylate (EA) to ethoxylated bisphenol A diacrylate (EBPAD) ratio directly supplied cyclopolymerizable resins with a broad range of viscosities and product distributions. Those resins produced from reaction mixtures rich in EA have low viscosities because of high diluent monomer contents and limited oligomerization of EBPAD due to end-cap formation. Resin viscosity and average molecular weight of the oligomeric component of the resin were inversely related to the amount of EA used in the reaction. Through the choice of reactants and their ratio, this simple technique has the potential to provide cyclopolymerizable resins for use in a variety of dental polymer applications.

Acrylates↗
PubMed1994

Physical and chemical properties of resin-reinforced calcium phosphate cements.

OBJECTIVES: The purpose of this study was to improve the handling and physical properties of a self-setting, water-based calcium phosphate cement by combining it with polymerizable resins and to study the setting reactions involved. METHODS: Dual-cured composite cements were prepared from a calcium phosphate cement powder and dental monomers that contain carboxylated hydrophilic resins or resin/water mixtures. The setting reaction of the calcium phosphate cement in the presence of the resins was evaluated by pH measurements, infrared spectroscopy, diametral tensile strength, x-ray diffraction analysis, and scanning electron microscopy. RESULTS: Carboxylated resins were chosen because they can form ionic bonds to the mineral filler, which was confirmed by appearance of an infrared absorbance peak at 1552 cm-1 within 24 h after mixing due to the formation of a carboxylate salt. Hydroxyapatite did not develop in composites prepared from resin and calcium phosphate cement. However, composites from calcium phosphate cement, resin and water showed approximately 40% hydroxyapatite. The resulting composite cements have moderately high DTS of 14-15 MPa and high pH. SIGNIFICANCE: Hydrophilic acidic resins allows mixing with water and/or allow rapid diffusion of water into the resinous cement so that the dissolution and reprecipitation processes required for the conversion of the calcium phosphate components to hydroxyapatite can occur. The characteristics of the resulting composite cements suggest that the materials may be useful in pulp capping and/or cavity lining.

Calcium Phosphates↗
PubMed1993

Modified surface-active monomers for adhesive bonding to dentin.

PMGDM, a PMDM-type adhesive monomer, was synthesized from pyromellitic dianhydride and glycerol dimethacrylate. Only the para isomer of PMDM, a solid, is used in dental adhesives. The adhesive monomer PMGDM is a liquid and consists of a mixture of para- and meta isomers. This study shows that PMGDM has several advantages over PMDM. For example, the adhesive can be applied at a greater thickness, and additives and/or additional initiators for improved curing can be incorporated. Use of the liquid monomer PMGDM also provided a convenient means of varying the thickness of the adhesive layer between dentin and composite. The adhesive bonds were tested in both shear and tensile modes. PMDM was used as the control. The reliability of the bonds, as judged from the Weibull modulus and Weibull characteristic strength, was improved by (1) use of more concentrated solutions of PMGDM adhesive, (2) use of an adhesive thickness of about 25 microns, and (3) modification of PMGDM with a diluent monomer which is expected to enhance the degree of cure and/or the dentin-wetting properties of the adhesive resin.

Adhesives↗
PubMed1993

Informed consent.

Explore the source record for details and available documents.

Contrast Media↗
PubMed1991

NIR-spectroscopic investigation of water sorption characteristics of dental resins and composites.

A near infrared (NIR) method using the 5200 cm(-1) absorption of water has been employed to examine water absorbed in photopolymerized dental resins and composites in the form of 0.01-cm- to 0.15-cm-thick specimens. The concentration, c [mol L(-1)], of absorbed water in specimens of thickness t [cm] was calculated by means of Beer's law, A = e ct. A is the NIR absorbance and e is the absorptivity of absorbed water. e depends on the environment of the water molecule and it is necessary to estimate e for water in each material. Water sorption was determined gravimetrically and correlated to the absorbance in the NIR spectrum. Once the relationship between e and water content was known for a material, water sorption was determined rapidly on very thin specimens for faster equilibration. Where dissolution of the specimen occurred, the solubility behavior of the specimen was evaluated from a comparison of NIR and gravimetric measurements. The NIR absorptivity, e, of water absorbed in a polymeric medium was found to be inversely related to the degree of hydrophilicity and hydrogen bonding capability of the polymer. The presence of water clusters in a polyethylene oxide methacrylate polymer was inferred from convex-up curvature in the plot of e vs. water content.

Absorption↗
PubMed1990

Ethical and legal dilemmas arising during predictive testing for adult-onset disease: the experience of Huntington disease.

The goal of predictive testing is to modify the risk for currently healthy individuals to develop a genetic disease in the future. Such testing using polymorphic DNA markers has had major application in Huntington disease. The Canadian Collaborative Study of Predictive Testing for Huntington Disease has been guided by major principles of medical ethics, including autonomy, beneficence, confidentiality, and justice. Numerous ethical and legal dilemmas have arisen in this program, challenging these principles and occasionally casting them into conflict. The present report describes these dilemmas and offers our approach to resolving them. These issues will have relevance to predictive-testing programs for other adult-onset disorders.

Abortion, Eugenic↗