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Biomedical subjects

E H Greener

Publications and source records attributed to E H Greener.

At least 91 records · Page 5Linked to original sources
PubMed1982

Properties of Ag-Cu-Pd dispersed phase amalgams: microstructures.

A 62% Ag-28% Cu-10% Pd lathe-cut alloy was successfully blended with conventional lathe-cut and spherical amalgam alloy. The resulting alloy showed little gamma 2 after one wk at 37 degrees C and a phase structure resembling commercial amalgam. In addition, the Cu3Pd phase present in the dispersant appears to participate in the amalgam reaction and, as a result, Pd may be found in the reaction zone around the dispersants in gamma 1 and/or Cu6Sn5 phases.

Chemical Phenomena↗
PubMed1981

The rheological properties of polyelectrolyte cements. I. polycarboxylates.

The rheological behaviour of six setting carboxylate cements was studied by capillary techniques in the shear rate of 0.65-65 s-1 and the cements were found to behave as power law fluids. All cements became dilatant as setting progressed and the kinetics of apparent viscosity increase, were found to follow an exponential function of time, exp (mt), with m congruent to 0.5.

Acrylic Resins↗
PubMed1981

The rheological properties of polyelectrolyte cements II. Glass ionomers.

The rheological properties of two glass ionomer cements, ASPA and Fuji have been investigated. The viscosities of the liquid components of these systems have been found to be Newtonian up to a shear rate of 140 s-1 with values of 0.80 N m-2 s for ASPA and 1.8 N m-2 for Fuji. Capillary viscometry techniques have been employed to study the rheological changes accompanying setting. Both cements appear to behave as power law fluids, becoming progressively dilatant as setting proceeds. The apparent viscosities of the two systems are approximately equivalent displaying values of the order of 50 N m-2 s, at a shear rate of unity shortly after mixing.

Chemical Phenomena↗
PubMed1981

Rheology of composite restoratives.

The components of Adaptic and Nuva-fil have been found to be the most viscous, while those of Concise were found to be the least viscous. The viscosity of setting systems revealed Adaptic to be the most viscous overall and Profile the least. All components and setting materials were shown to be pseudoplastic, with flow properties most likely controlled by the resin phase. The cone and plate have been found to be a feasible method for working time determination, with Profile having an extended working period, compared to the other systems tested.

Composite Resins↗
PubMed1981

Rheology of acrylic bone cements.

The rheological properties of setting acrylic bone cements were examined with a rotational cone and plate viscometer. The cements were tested over two orders of magnitude of shear rate to determine the nature of any non-Newtonian flow behavior. All three cements behaved with moderate pseudoplasticity (i.e., shear thinning) during setting, suggesting the use of higher pressures during administration for better flow and penetration. The low viscosity brand was found to be nearly one-half as viscous as the conventional cements during the working time (i.e., 2-5 minutes). A series of sieving experiments were performed to determine the particle size distributions of the powder components. Statistical analysis (chi square) showed the cements to have different distributions, with the low viscosity brand containing a larger proportion of smaller polymer particles. This difference is thought to contribute to the lower viscosity of this cement.

Bone Cements↗
PubMed1980

Time-temperature behavior for creep of dental amalgam.

From 0 to 24 hours at an initial static stress of 34.5 MPa and in the temperature range of 0 to 60 degrees C, the creep behavior of four different one-week-old dental amalgams was monitored in a recently developed mini-specimen creep apparatus. In most instances the behavior could not be described by a linear relationship. Therefore, the usefulness of calculating creep rate based upon only two times, i.e., 1 and 4 hours, must be questioned. On the other hand, the observed creep kinetics were found to follow accepted nonlinear models of dislocation/obstacles interactions which may be thermally activated.

Cold Temperature↗
PubMed1980

Characterization of some denture cleansers.

1. From comparison of calculated reaction times for homogeneous H2O2 aqueous decomposition containing alkali to the measured rates of H2O2 dissociation in the cleanser systems, it is apparent that the cleansers are further catalyzed either heterogeneously and/or homogeneously. Long-term O2 measurements indicate cleansers with O2 concentrations similar in magnitude to concentrations observed at early times. First-order reaction times, as well as the high solubility of O2 in water, can explain these high long-term O2 concentrations. 2. The process of catalyzing the H2O2 to O2 varies with cleanser product. Cleansers like Efferdent, Polident, and Kleenite exhibit high H2O2 concentration changes and high O2, suggesting the decomposition of H2O2 to O2. DOC exhibits high H2O2 concentration changes and low O2, suggesting the H2O2 decomposition via the perhydroxyl ion, HO2-. 3. The CO2-H2O system contributes to the aqueous chemistry of the slightly basic cleansers of Efferdent and Polident. Measured CO2 concentrations of these cleansers were high in comparison to the more basic cleansers of Kleenite and DOC. 4. Differentiation of the cleansers were made in terms of the Cl- concentration. Kleenite exhibited Cl- concentrations at least 10(2) times the concentrations found in Efferdent and Polident.

Boron↗
PubMed1980

Capillary rheology of two composite resin systems.

The rheological properties of two commercial resin systems, Isopast and Cosmic, were studied in the shear rate range 0.65-65 s-1 by capillary techniques. Isopast represents a low inorganic filled composite, whereas Cosmic is a conventionally filled system whose resin matrix resembles that of Isopast. All components of both systems obeyed power law dependence of shear stress as a function of shear rate according to the relation 1n tau = 1n K + n 1n gamma; values of n for Cosmic catalyst and paste and Isopast paste were of the order of 0.6 whereas Isopast catalyst was of the order of 0.3. Setting systems obeyed a power law relationship during the working time with an exponent n congruent to 0.7-1.0. Accordingly the systems appear pseudoplastic in component form and slightly pseudoplastic to near Newtonian after mixing.

Chemical Phenomena↗
PubMed1979

A clinical study of marginal integrity and tarnish behaviour of three Cu-rich amalgam systems.

Three high Cu-gamma2 free amalgams and one conventional amalgam were used in a clinical study to evaluate degree of marginal integrity and surface discoloration occurring for time periods of up to two years. Two hundred and seventy restorations were placed in Class I and II cavities in sixty-two paedodontic patients. Amalgams were prepared from conventional alloy, Cu admixed, Dispersalloy and three parts 50Ag-20Sn-30Cu mixed with one part conventional alloy. Restorations were evaluated by three groups of clinicians. Ridit means obtained from all three groups of evaluations were in good agreement. The lower ridits indicate better marginal integrity and less tarnish. Marginal integrity of amalgams prepared from Cu-admix did not differ appreciably (0.41) from the ridit associated with initial placement (0.39). Conventional amalgams had the highest ridit (0.65) for marginal integrity whereas the ternary/conventional and Dispersalloy restorations were intermediate (0.55 and 0.52). The ridit for tarnish and surface discoloration was decidedly higher for the Cu-admix (0.73) than for the other systems investigated which had ridits of the order of 0.50 compared to an initial ridit for tarnish of 0.28.

Analysis of Variance↗
PubMed1979

Mechanism of chloride corrosion of dental amalgam.

Polarization of conventional dental amalgam in Ringer's solution produces a dissolution of the gamma 2 phase at--250 mV (SCE) and formation of Sn-Cl and Sn-O-Cl. This study was undertaken to determine the electrochemical nature of these reactions. Potentiostatic polarization scans were run at 4, 37 and 50 degrees C in several dilutions of aerated Ringer's solution. Manipulation of reactant concentrations and electrolyte temperature produced shifts in the potentiostatic profiles. At 50 degrees C, a gamma 2 dissolution peak shift to -300 mV was observed, and at 4 degrees C the peak shifted to -200 mV. Dilution of Ringer's solution with respect to [Cl-] over three orders of magnitude produced a linear shift in the noble direction of 500 mV. Cathodic polarization appears to be limited by the oxygen half cell reaction. Changes of [Cl] affect the shape of the peak, round out its approach to the current maximum. Shifts in peak potential due to temperature and concentration changes agreed with calculations based on critical pitting potential for gamma2 dissolution due to a chloride reaction. Polarization profiles in pooled saliva agreed with calculated potentials based on known saliva [Cl-].

Chemical Phenomena↗
PubMed1978

Role of mucin and albumin in saline polarization of dental amalgam.

Studies into the electrochemical nature and corrosion behaviour of dental amalgam have indicated the need for an artificial saliva formula that will accurately simulate the electrochemical properties of natural saliva. Existing formulae have been based on inorganic saliva constituent concentrations, without accurate representation of organic constituents. Albumin and mucin were added to several dilutions of saline solution. The resulting solutions were used as electrolyte at 4 degrees and 37 degrees C for the potentiostatic anodic polarization of conventional amalgam. The presence of albumin and mucin did not appear to alter the major characteristics of corrosion profile. Examination of the current-time transient curves indicated, however, that the kinetics of the electrochemical reactions were delayed. Also, the open circuit potential was observed to shift to more active values with the addition of organic constituents, thereby creating a low current density region in the initial segment of the polarization profile.

Albumins↗