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Biomedical subjects

N Horasawa

Publications and source records attributed to N Horasawa.

5 recordsLinked to original sources
PubMed1999

Galvanic interaction between titanium and gallium alloy or dental amalgam.

OBJECTIVES: The objective was to examine in vitro the galvanic interaction between titanium and a high-copper dental amalgam or a gallium-based direct filling alloy at different area ratios, and to relate the observed interactions to the electrochemical characteristics of the alloys. METHODS: The tested materials were cast titanium, a single-composition, spherical high-copper amalgam, and a gallium-based direct filling alloy. Polarization curves were recorded. The galvanic couples were prepared at Ti/filling alloy ratios of 1:1, 2:1, 4:1 and 6:1. The couples were exposed to synthetic saliva at 37 degrees C and the galvanic currents and potentials were measured as a function of time. The results were analyzed by ANOVA and Tukey tests (p < or = 0.05). RESULTS: Freshly abraded titanium initially was anodic to both the amalgam and the gallium alloy, but the polarity reversed after a period of exposure. The galvanic potential and current density increased with the increasing Ti/alloy area ratio. The potential increase was smaller and the current increase larger for the Ga alloy than for the amalgam. The difference was consistent with the polarization characteristics. The galvanic current density was of the order of 10(-8) A/cm2 for the Ti/amalgam couple, and 10(-7) to 10(-6) A/cm2 for the Ti/gallium alloy couple. SIGNIFICANCE: The results show that the galvanic interaction between titanium and direct filling alloys is small. High copper dental amalgams should suffer little galvanic corrosion when in contact with Ti. For gallium direct filling alloys, the galvanic interaction may be more detrimental because of the inherently lower corrosion resistance.

Analysis of Variance↗
PubMed1997

Behavior of pure gallium in water and various saline solutions.

This study investigated the chemical stability of pure gallium in water and saline solutions in order to obtain fundamental knowledge about the corrosion mechanism of gallium-based alloys. A pure gallium plate (99.999%) was suspended in 50 mL of deionized water, 0.01%, 0.1% or 1% NaCl solution at 24 +/- 2 degrees C for 1, 7, or 28 days. The amounts of gallium released into the solutions were determined by atomic absorption spectrophotometry. The surfaces of the specimens were examined after immersion by x-ray diffractometry (XRD) and x-ray photoelectron spectroscopy (XPS). In the solutions containing 0.1% or more NaCl, the release of gallium ions into the solution was lowered when compared to deionized water after 28-day immersion. Gallium oxide monohydroxide was found by XRD on the specimens immersed in deionized water after 28-day immersion. XPS indicated the formation of gallium oxide/hydroxide on the specimens immersed in water or 0.01% NaCl solution. The chemical stability of pure solid gallium was strongly affected by the presence of Cl- ions in the aqueous solution.

Dental Alloys↗
PubMed1996

Cyclic voltammetry of dental amalgams.

OBJECTIVES: This study used cyclic voltammetry to examine the effect of the composition of dental amalgams on their electrochemical behavior, including reactions occurring outside of oral conditions. METHODS: Amalgams (residual mercury 47.5%) were prepared using two low-copper (3 wt% Cu) powders and five high-copper powders (40-80 wt% Ag, 12-30 wt% Cu) with and without zinc (1.5 wt%). Cyclic voltammograms were obtained at 37 degrees C in 1.0% NaCl scanning at 2 mV/s in the potential range from -1.5 V to +0.8 V vs. Ag/AgCl. RESULTS: During the anodic scans, AgCl and Hg2Cl2 films were formed on all amalgams except the one with only 40 wt% Ag. In all high-copper amalgams, a prominent Cu (oxidation) peak was found at -0.1 V, indicating the release of copper during corrosion. Zinc affected the oxidation process for both low- and high-copper amalgams. When zinc was absent, a peak for Sn2+ oxidation appeared at -0.4 V. When zinc was present, a Sn4+ oxidation peak was revealed at -0.6 V. In some amalgams, there was evidence of the selective corrosion (pitting corrosion) of tin and copper. In the lowest silver-content amalgam, no protective films were formed, which is indicative of its poor corrosion resistance. As expected, in all the low-copper amalgams, an extreme increase in current density was recorded immediately at 0 V, due to the release of tin from gamma 2. SIGNIFICANCE: Cyclic voltammetry is useful for the rapid examination (less than an hour) of the electrochemical behavior of amalgams, specifically to obtain information on the formation of compounds and the sequences of electrochemical reactions.

Analysis of Variance↗
PubMed1989

[Electrochemical stability of dental materials. Part 4. Immersion test of amalgam].

Specimens prepared with three commercial dental amalgams were immersed in three kinds of solutions: Ringer's, 1% lactic acid and 0.05% hydrochloric acid, at 37 degrees C, and subjected to a repeated corrosion test for fifteen weeks. Quantitative analysis was performed by inductively coupled plasma emission spectrometry for released metal elements to determine the composition of these amalgam alloy powders and immersed specimens. The immersion test for one week was not sufficient to prove the corrosion tendency of amalgam and a longer period of immersion was considered necessary. The kinds and amounts of released elements in each solution differed, and the corrosion tendency of high copper amalgam differed from that of conventional amalgam.

Copper↗