Chemical passivation as a method of improving the electrochemical corrosion resistance of Co-Cr-based dental alloy.

PURPOSE: The purpose of the study was to evaluate corrosion resistance of Wirobond C® alloy after chemical passivation treatment. METHODS: The alloy surface undergone chemical passivation treatment in four different media. Corrosion studies were carried out by means of electrochemical methods in saline solution. Corrosion effects were determined using SEM. RESULTS: The greatest increase in the alloy polarization resistance was observed for passive layer produced in Na2SO4 solution with graphite. The same layer caused the highest increase in corrosion current. Generally speaking, the alloy passivation in Na2SO4 solution with graphite caused a substantial improvement of the corrosion resistance. The sample after passivation in Na2SO4 solution without graphite, contrary to others, lost its protective properties along with successive anodic polarization cycles. The alloy passivation in Na3PO4 solution with graphite was the only one that caused a decrease in the alloy corrosion properties. The SEM studies of all samples after chemical passivation revealed no pit corrosion - in contrast to the sample without any modification. CONCLUSIONS: Every successive polarization cycle in anodic direction of pure Wirobond C® alloy enhances corrosion resistance shifting corrosion potential in the positive direction and decreasing corrosion current value. The chemical passivation in solutions with low pH values decreases susceptibility to electrochemical corrosion of Co-Cr dental alloy. The best protection against corrosion was obtained after chemical passivation of Wirobond C® in Na2SO4 solution with graphite. Passivation with Na2SO4 in solution of high pH does not cause an increase in corrosion resistance of WIROBOND C. Passivation process increases alloy resistance to pit corrosion.

Development of binary and ternary titanium alloys for dental implants.

OBJECTIVE: The aim of this study was to develop binary and ternary titanium (Ti) alloys containing zirconium (Zr) and niobium (Nb) and to characterize them in terms of microstructural, mechanical, chemical, electrochemical, and biological properties. METHODS: The experimental alloys - (in wt%) Ti-5Zr, Ti-10Zr, Ti-35Nb-5Zr, and Ti-35Nb-10Zr - were fabricated from pure metals. Commercially pure titanium (cpTi) and Ti-6Al-4V were used as controls. Microstructural analysis was performed by means of X-ray diffraction and scanning electron microscopy. Vickers microhardness, elastic modulus, dispersive energy spectroscopy, X-ray excited photoelectron spectroscopy, atomic force microscopy, surface roughness, and surface free energy were evaluated. The electrochemical behavior analysis was conducted in a body fluid solution (pH 7.4). The albumin adsorption was measured by the bicinchoninic acid method. Data were evaluated through one-way ANOVA and the Tukey test (α=0.05). RESULTS: The alloying elements proved to modify the alloy microstructure and to enhance the mechanical properties, improving the hardness and decreasing the elastic modulus of the binary and ternary alloys, respectively. Ti-Zr alloys displayed greater electrochemical stability relative to that of controls, presenting higher polarization resistance and lower capacitance. The experimental alloys were not detrimental to albumin adsorption. SIGNIFICANCE: The experimental alloys are suitable options for dental implant manufacturing, particularly the binary system, which showed a better combination of mechanical and electrochemical properties without the presence of toxic elements.

Mechanical, physical, and chemical characterization of Ti-35Nb-5Zr and Ti-35Nb-10Zr casting alloys.

Titanium is used due its excellent properties in medical and dentistry areas. With the objective of exploiting better mechanical properties, not altering its biocompatibility, it was intended to add niobium and zirconium to the titanium, being formulated two alloys Ti-35%Nb-5%Zr (alloy 1) and Ti-35%Nb-10%Zr (alloy 2) wt% produced by an arc melting method. The chemical analysis of the samples was accomplished by X-ray fluorescence, and the microstrutural evaluation by scanning electron microscopy and X-ray diffraction. The mechanical tests were: Vickers hardness, tensile strength, mechanical cycling, and fracture analysis. The results allowed characterizing the alloy 1 as alpha + beta type and the alloy 2 as beta type. It is found that the alloy 1 presented larger hardness and smaller tensile strength than the alloy 2. The fractures, after the tensile test, were of the ductile type and, after the mechanical cycling, they were of the mixed type for both alloys.

Electrochemical characterization and immersion corrosion of a consolidated silver dental biomaterial.

A consolidated silver (CS) material, an alternative to dental amalgam, was studied for corrosion. Chemically precipitated silver particles were acid activated and pressure consolidated to a volume porosity of 25%. In selected tests comparisons were made between CS and melted and cast silver particles (MS), silver with a known mass fraction purity of 99.998% (FS), a silver-palladium alloy (SP). and a dispersed-phase amalgam (DA). Fusayama artificial saliva was used with controlled variations in pH, sulfide content, mucin content, and absorbed oxygen content. Electrochemical polarization, electrochemical impedance spectroscopy, and immersion methods were used. Results revealed differences in the zero current potentials E(I = 0) from forward polarization between CS and MS (or FS) in deaerated solution. By superposition of the cathodic polarization curves, the area for CS was increased by 7.3 times and was enclosed within an outer shell of material 5.5 microm thick. Polarization resistance was significantly the highest for SP, followed in order by MS (or FS) and CS or DA. With scanning electron microscopy, CS was shown to be significantly more susceptible than MS to long-term immersion corrosion. The modeled equivalent electrical circuits for CS and DA involved a double layer capacitance, a charge transfer resistance, and an element attributed to adsorption. The active pore depth for CS from the transmission line model for porous solids revealed satisfactory agreement with polarization results. It is concluded that the corrosion susceptibility of CS in Fusayama solution, while similar to that for DA, is greater than it is for MS.

Cold crucible levitation melting of biomedical Ti-30 wt%Ta alloy.

Recently, titanium-tantalum alloys have been studied as implant materials for dental and orthopedic surgery. However, titanium and tantalum are difficult to mix by common arc melting and induction melting, because of their high melting point and the marked difference between their densities (Ti: 1,680 degrees C, 4.5 g/cm3, Ta: 2,990 degrees C, 16.6 g/cm3). Thus, the Cold Crucible Levitation Melting (CCLM) method was chosen to produce a Ti-30 wt%Ta binary alloy in the present study. The CCLM furnace, with 1 kg capacity, consisted of a water-cooled crucible comprising oxygen-free high purity copper segments and coils wrapped around the crucible and connected to a frequency inverter power supply. A qualified ingot of 1.0 kg of Ti-30 wt%Ta alloy was obtained. The ingot was characterized from the surface quality, chemical composition distribution and microstructure, and finally the melting process was discussed.

[The researches on titanium and titanium alloy in dental use].

Although titanium and titanium alloy have been used in dental field for several years because of their excellent biocompatibility, corrosion resistance and mechanical properties, many practical problems remain to be solved. This review focuses on the practical problems and the prospects of the researches on titanium, including the development of new titanium alloy, the surface treating, the corrosion in oral, and the processability.

[The forming phase and various properties of Au, Ag, Cu and Ga mixture in metal fired crowns].

A new time-saving method has been developed to produce artificial crowns without using the casting process. Plastic mixtures of gallium and other metal particles are kneaded into desired shape and then heated for hardening. By this method, the time required for hardening and producing restorative materials has been shortened greatly. In the present experiment, gallium was triturated with powdered gold, silver and copper to make binary alloy samples. The dimensional change was measured between heat treatment. After heat treatment, the test piece was examined for compressive strength, compressive shrinkage, hardness, tarnishing and difference in phase. Non-heated and heated alloy specimens (Au-Ga, Ag-Ga, Cu-Ga) expanded to form the new phase. The ability of Au-Ga samples to bear compressive strength, when heated at 300 degrees C or more (AuGa2----AuGa), became 2.6 times greater than that of non-heat-treated specimens. The compressive strength of Ag-Ga samples dropped briefly at 350 degrees C (Ag0.72Ga0.28----Ag3Ga) but increased at 450 degrees C (Ag3Ga----AgGa). The strength of Cu-Ga pieces fell by half at 475 degrees C and upward (CuGa2----unknown phase). A compression test showed that the contraction percentage of Au and Ag specimens became large as a result of heat treatment, while that of Cu alloys remained almost unchanged. The results of a hardness test (HV) were comparable to those of the compressive strength test. The Au-Ga alloys increased in hardness after high-temperature treatment. In the Ag-Ga alloys, hardness declined at 350 degrees C and increased at 450 degrees C. There was no difference in hardness between Cu specimens after heat treatment and those allowed to stand at room temperature. A tarnishing test revealed that Au-Ga samples turned slightly yellowish. In the case of Ag-Ga samples, the reflectivity Y (%) dipped slightly but discoloration was not recognizable. However, the Cu-Ga samples which were heated at temperatures of up to 280 degrees C showed a slight drop in reflectivity, but those heated at temperatures higher than 280 degrees C decreased to 50-66% in reflectivity and turned black.