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Biomedical subjects

E H Greener

Publications and source records attributed to E H Greener.

At least 19 recordsLinked to original sources
PubMed1992

Microstructures of admixed amalgams produced from Pd-containing dispersants.

Blended Pd-containing dental amalgams were developed by substituting Pd for up to 20 w/o Ag or Cu in the Ag-Cu eutectic alloy. Melted ingots were lathe-comminuted to a particle size distribution of 1-45 microns. Alloy blends were created from two parts of a traditional amalgam and one part of experimental Ag-Cu-Pd particles. Amalgams with from 0.42 to 1.67 w/o Pd were fabricated by trituration of alloys and mercury at a Hg/alloy ratio of 1:1 with a mechanical triturator at 5000 rpm for 10 s and hand-condensed. XRD studies of these amalgams revealed the suppression of eta' (Cu6Sn5) phase with Pd addition and no gamma 2 (Sn8Hg) phase found. At 3.3 w/o Pd, the eta' (Cu6Sn5) concentration of the amalgam was below the detection limit of the instrumentation (1%). SEM micrographs revealed that reaction zones around eutectic particles decreased with increased Pd concentration.

Dental Amalgam↗
PubMed1991

Microstructures of Pd-containing dispersants for admixed dental amalgams.

Blended Pd-containing dispersants were developed by the utilization of a Ag-Cu eutectic into which Pd was substituted for Ag or Cu in concentrations of up to 20 wt%. Compositions were melted either in argon-filled sealed vycor tubes or in a graphite-linked carbon crucible of an induction furnace with an argon blanket. Ingots of approximately 1.5 cm in diameter were sectioned to 0.2 cm in thickness and polished through standard metallographic polishing procedures. The possible compounds were identified by XRD. The microstructures of the alloys were examined by SEM/EDS. XRD analysis of the alloys revealed the preferential dissolution of Pd in Cu when the Pd concentration was less than or equal to 10 wt%. When the Pd concentration exceeded 20 wt%, Pd was found to be dissolved in both Ag and Pd. No Cu3Pd x-ray diffraction peaks were found for alloys with Pd concentration of up to 20 wt%. SEM/EDS analysis confirmed XRD results; lamellae of Ag and Cu-Pd were found in alloys with Pd concentration less than or equal to 10 wt%.

Copper↗
PubMed1991

Non-linear in vitro wear of posterior composites with time.

Several clinical studies have found the wear rate of posterior composites to be nonlinear, with greater wear occurring initially. This relationship and its causes were sought in an in vitro test that used the Taber Abraser. Three commercial composites--Marathon, Occlusin, and P-30--were tested. Sixteen cured samples of each were initially finished with 600-grit paper and then abraded by medium-grit wheels for 30,000 cycles. Periodically, the weight losses were recorded and then converted to volume losses. Analysis included comparison of volume losses per 5000-cycle interval and comparison of first derivatives (wear rate) and second derivatives of the best-fit second-order regression line. Significant differences (p less than 0.05), as analyzed by ANOVA, were consistently realized between the volume losses for the first interval and those for subsequent intervals. Rank, with regard to wear resistance, depended on whether volume loss or initial wear rate was compared. The Taber Abraser did show non-linear trends similar to those observed clinically. Initial surface preparation, which apparently contributes to the greater early wear rates recorded in this in vitro study, may also be a factor clinically.

Analysis of Variance↗
PubMed1990

Dynamic mechanical properties of dental amalgams.

The dynamic mechanical properties of two high-copper amalgams (Tytin and Dispersalloy) and two traditional amalgams (Aristalloy and Aristalloy with Zn) were measured over a temperature range of 0-70 degrees C and at frequencies of 0.1, 1, and 10 Hz by means of a DuPont DMA. Values of storage modulus (E') for the amalgams were equivalent to the Young's modulus (E) measured from static mechanical test methods, with Dispersalloy demonstrating the highest moduli. Values of E' decreased with increased temperature. E' of traditional amalgams decreased more rapidly than did those of the Cu-rich amalgams. Values of loss modulus (E") for Tytin were smaller than those of Dispersalloy and the two types of Aristalloy. High values of E" for the traditional amalgams correspond to a greater viscous behavior. Marked differences between the magnitude of tan delta and its temperature coefficients for traditional and high-copper amalgams were observed, which is indicative of differences in visco-elastic behavior between these two amalgam systems.

Copper↗
PubMed1990

Cu-Ti, Co-Ti and Ni-Ti systems: corrosion and microhardness.

Titanium alloys of 10 wt%-72 wt% Cu, 10 wt%-80 wt% Co and 20 wt%-84 wt% Ni were investigated. Ingots were fabricated in a vacuum/argon tungsten arc furnace. The surfaces of the alloys were examined by optical microscopy and SEM/EDS, and the Knoop hardness values of the alloys were measured. The corrosion resistance of the alloys was determined by a potentiodynamic polarization technique in buffered Ringer's solution. When a threshold composition of 30 wt% alloy was reached, a large decrease in corrosion resistance was found to occur. Knoop hardness measurements showed that similar hardness values of approximately 300 KHN can be obtained in all systems with lower alloy content. These values are similar to those obtained with a commercial dental titanium alloy.

Chemical Phenomena↗
PubMed1990

Correlation between degree of conversion, filler concentration and mechanical properties of posterior composite resins.

The degree of conversion, filler concentration and mechanical properties of seven proprietary light-cured posterior composite resins were investigated. The degree of conversion of composites ranged from 43.5-73.8%. The weight fraction of filler that was obtained was in the range 66.4-85.2%. The volume fraction varied from 58.2-74.2%. The mean values of the observed compressive and diametral tensile strengths ranged from 242.3-324.7 MPa and from 39.8-62.6 MPa, respectively. The Knoop hardness numbers ranged from 41.8-81.9. Significant correlations were observed between the volume fraction of filler and the diametral tensile strength (r = 0.89), and between the volume fraction of filler and the Knoop hardness number (r = 0.89). No correlation was found between the degree of conversion and any of the mechanical properties of the composite resins tested. Because of the positive correlations between the volume fraction of filler and the diametral tensile strength, and between the volume fraction of filler and the Knoop hardness numbers, it is concluded that the filler concentration plays a prominent role in determining the properties of contemporary posterior composite resins.

Analysis of Variance↗
PubMed1990

Casting pure titanium into commercial phosphate-bonded SiO2 investment molds.

Pure titanium was cast into five different phosphate-bonded SiO2 investment mold materials (at 350 degrees C) with an argon-arc melting and pressure casting machine. The mesh castability, the fit of the MOD inlay castings, and the Knoop hardness and the micro-structure in cross-sections of castings were examined. The setting and thermal expansion, the compressive strength, and the X-ray diffraction analysis of the investments were also measured. The castability, the fit, and the thickness of the reacted layer differed in degree among these investments, in spite of the same phosphate-bonded SiO2-type investment. A significant correlation was obtained between the thermal expansion (at 350 degrees C) and the casting accuracy.

Analysis of Variance↗
PubMed1989

Studies of Ti alloys for dental castings.

Casting of Ti has been recently investigated in dentistry. The purpose of this study was to examine the alloying effect on the cast Ti. Metallurgical structures, mechanical properties, and in vitro corrosion resistance were, therefore, studied for cast Ti and for four selected cast Ti alloys such as Ti-6AI-4V, Ti-15V, Ti-20Cu, and Ti-30Pd. A "Castmatic" dental casting machine was utilized, which involved argon-arc melting and subsequent argon/vacuum-pressurized casting. The photomicrographs revealed quite large grains in the cast structures. XRD analyses on cast Ti metals showed the quasi-equilibrium phases present. The strength of cast Ti could be significantly increased by alloying. Cross-sectional microhardness measurements of cast Ti alloys showed U-type hardness distribution due to the surface mold reaction. All the cast Ti alloys examined showed a strong passivity trend in the corrosion test. The present results suggest that cast Ti alloys have promising features for future dental uses.

Dental Alloys↗
PubMed1989

Metallurgical aspects and corrosion behavior of yellow low-gold alloys.

Three copper-free type III yellow low-gold alloys (Ag-Au-In-Pd-Zn) were investigated. Microstructural analysis was performed with x-ray diffraction, light microscopy, and an electron x-ray micro-analysis. The electrochemical behavior of the alloys was tested with standard potentiodynamic techniques in 0.9% saline solution and an artificial saliva and compared with that of a traditional high-gold alloy. The three alloys turned out to be two-phase mixtures of a fcc (matrix) and a bcc (island) phase. The yellow color, present in spite of the low-gold content, was caused by the disordered Pd-In, island-type structure. An additional third structure was seen after etching. However, no distinct phase could be correlated with it. The corrosion behavior for the experimental alloys, based on cyclic polarization, can be considered acceptable in both electrolytes used, but is inferior to that of the control alloy.

Corrosion↗
PubMed1989

The corrosion behavior of palladium-silver-ceramic alloys.

Five commercial Pd-Ag alloys were investigated. Their electrochemical behavior was tested with standard potentiodynamic techniques in 0.9% saline solution and an artificial saliva and compared with high-Pd systems. Corrosion characteristics of the Pd-Ag alloys were quite similar regardless of microstructural and compositional differences. In the area of oral interest, all alloys showed a sufficient corrosion resistance. The alloys were, unlike their high-Pd counterparts, adversely affected by a high Cl- content under more extreme conditions, and a visible film formed.

Ceramics↗
PubMed1989

The corrosion behaviour of high-palladium porcelain-bonding alloys.

The corrosion behaviour of eight commercial high-Pd alloys was investigated and compared to that of Pd-Ag systems. They were tested with standard potentiodynamic techniques in 0.9 per cent saline solution and an artificial saliva. The corrosion behaviour of the high-Pd alloys was satisfactory and essentially equivalent. In more systems anodic overloading in 0.9 per cent saline in this alloy group seemed to be superior compared to the Pd-Ag alloy group. Within the high-Pd alloy systems compositional and constitutional variations were apparently too small to result in substantial electrochemical effects.

Corrosion↗
PubMed1989

Metallurgical aspects of palladium-silver porcelain-bonding alloys.

Metallurgical aspects of five commercial Pd-Ag porcelain-bonding alloys have been investigated using X-ray diffraction, light microscopy and X-ray microanalysis. All alloys are mainly single-phase systems, but they appear to be inhomogeneous due to constitutional supercooling. Porcelain firing times are presumably insufficient to reach homogeneity. Two alloys show a virtually identical chemical composition but a differing amount of segregation which should be attributed to minor components controlling the solid diffusion process. Both indium-containing alloys show signs of a minor second phase which could not be identified due to its finely dispersed character.

Dental Alloys↗
PubMed1989

Effect of mucin on the corrosion behaviour of dental casting alloys.

The influence of mucin on the corrosion behaviour of seven typical dental casting alloys was investigated. A commercial saliva substitute (Saliva Orthana) containing mucin, and a control from which the mucin had been removed, were used. The electrochemical behaviour of the test alloys was evaluated around the open circuit potential (OCP) utilizing standard potentiodynamic techniques, as a function of oxygen concentrations and pH. The results of the corrosion measurements were analysed by a four-way ANOVA to detect the influence of alloy, environment and possible interactions. Mucin seems to act as a cathodic inhibitor at pH 6.7 but not at pH 4.6. An unidentified component (e.g. benzoate) of the saliva substitute probably acts as an adsorption inhibitor. Anodic passivation is also correlated with the artificial saliva composition.

Analysis of Variance↗