Potentiodynamic polarization study of the corrosion behavior of palladium-silver dental alloys

Effect of disinfectants on multispecies biofilm, the physical and mechanical properties of polymethyl methacrylate, and the corrosion of cobalt chromium alloy

STATEMENT OF PROBLEM

The optimal disinfection protocol that controls adverse effects and promotes effective antimicrobial action on removable prostheses is unclear.

PURPOSE

This in vitro study investigated the effect of disinfectant solutions on the biological, physical, mechanical, and chemical properties of removable prosthesis materials.

MATERIAL AND METHODS

Specimens of polymethyl methacrylate (PMMA) and cobalt chromium (Co-Cr) alloy were immersed in distilled water (PMMA) or artificial saliva (Co-Cr) as the control and in 0.25% sodium hypochlorite (NaOCl0.25%), 0.5% chloramine T (CT0.5%), and 0.15% Triclosan (TR0.15%). The antibiofilm activity was evaluated by microbial load and cell metabolisms of the mixed biofilm. Physical (color change, sorption, solubility, and surface roughness), mechanical (hardness, flexural, and impact strength), and chemical (corrosion) properties were analyzed before and after simulating a 5-year immersion. Laser confocal microscopy, scanning electron microscopy (SEM), and dispersive energy spectroscopy (EDS) complemented the analyses. The data were analyzed by using the Mann-Whitney U test, Kruskal-Wallis with Dunn posttests, 1-way ANOVA, and repeated measures ANOVA (α=.05).

RESULTS

All solutions were effective against bacteria, but only NaOCl0.25% eliminated Candida spp. TR0.15%, and CT0.5% increased cell metabolisms. For interaction (time and solution), there was a reduction in PMMA hardness in the control and TR0.15%. Color, sorption, solubility, and flexural strength did not change. CT0.5% and TR0.15% were similar for impact resistance. CT0.5% caused the lowest roughness. NaOCl0.25% showed the greatest corrosive potential. Dark spots were seen under SEM in Co-Cr stored with NaOCl0.25% and TR0.15%. EDS indicated different proportions of oxygen, cobalt, chromium, and molybdenum.

CONCLUSIONS

NaOCl0.25% had the best antimicrobial action. CT0.5% and TR0.15% have potential. Hardness and roughness changes were clinically acceptable, and the other properties remained unchanged. All the solutions caused color changes. NaOCl0.25% was unsatisfactory for use with Co-Cr, CT0.5% was intermediate, and TR0.15% was suitable.

Cytotoxicity of Commercially Pure Titanium (cpTi), Silver-Palladium (Ag-Pd), and Nickel-Chromium (Ni-Cr) Alloys Commonly Used in the Fabrication of Dental Prosthetic Restorations

INTRODUCTION

The longevity of dental implants is affected by the ability to avoid any hypersensitivity or corrosive reactions in the oral cavity. The aim of the current study was to evaluate the cytotoxic effect of commercially pure titanium (cpTi), silver-palladium (Ag-Pd), and nickel-chromium (Ni-Cr) on human gingival fibroblast (HGF).

METHODS

The sample size used was 10 discs from each alloy used with dimensions of 4x3mm. The HGF was derived from healthy patients subjected to gingivectomy procedures. Of the specimens, 50% were incubated in artificial saliva and the other half in Dulbecco's Modified Eagle medium (DMEM). The extract of each alloy in both media was collected and applied on HGF. After 24 hours the morphology of the HGF cells was examined to detect any apoptosis or cell death. Also, cell viability was evaluated by the use of a 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Statistical analysis was performed using students' t-test and two-way ANOVA with a significance level of p<0.05.

RESULTS

In the case of morphological examination of HGF and MTT assessment, only cpTi alloy specimens didn't display any cytotoxic effect. Ni-Cr was the most cytotoxic alloy of the three. Also, MTT activities of all three alloys were decreased when they were incubated in artificial saliva.

CONCLUSION

cpTi exhibited the highest corrosion resistance in comparison to Ag-Pd and Ni-Cr alloys. Ag-Pd alloys showed acceptable resistance to corrosion that is due to the passivity effect. Also, artificial saliva increased the cytotoxic effect of the tested alloys more than DMEM.

Effect of the Alloying Metal on the Corrosion Resistance of Pd-Rich Binary Alloys with Pt, Rh, and Ru in Sulfuric Acid

The paper presents the study of the corrosion resistance of electrodeposited Pd and its binary alloys with Pt, Rh, and Ru on a polycrystalline Au substrate. The corrosion resistance was tested in 0.5 M sulfuric acid at room temperature using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The morphology/composition and work function values were determined by scanning electron microscopy/energy-dispersive X-ray spectroscopy and scanning Kelvin probe, respectively. The obtained results revealed that the Pd electrode is the most resistant to corrosion, whereas the Pd-Ru electrode is the most susceptible to dissolution. It was found that the corrosion resistance of Pd-binary alloys decrease in the following order: Pd > Pd-Pt > Pd-Rh > Pd-Ru. This effect was assigned mainly to the difference in surface roughness factor of tested electrodes.

Electrochemical impedance spectroscopy study of corrosion characteristics of palladium-silver dental alloys

Electrochemical impedance spectroscopy (EIS) has been used to obtain insight into corrosion processes for three Pd-Ag alloys, and compare their behavior with an Au-Pd alloy. Five specimens of each alloy received clinically-appropriate simulated porcelain-firing heat treatment. EIS testing was performed at ambient temperature, using 0.09% NaCl, 0.9% NaCl and Fusayama solutions. EIS data are presented as Bode plots. At the open-circuit potential (OCP), the data fit a modified Randles equivalent electrical circuit with a constant phase element (CPE), and the charge-transfer resistance (R_CT ) and the two CPE parameters (CPE-T and CPE-P) were determined. The area-normalized capacitance of the double layer (C_dl ) was also calculated. The EIS data at two relevant elevated potentials in the passive range were also found to fit well a modified Randles equivalent circuit with different values for the charge transfer resistance and CPE parameters. At the OCP no significant effect on R_CT was found for the alloys and electrolytes, and both alloy and electrolyte significantly affected CPE-P. In vitro corrosion was controlled by charge transfer and charge accumulation processes, and the behavior differed at the elevated potentials compared to the OCP. Significant effects were found for alloy, electrolyte, and alloy/electrolyte interaction on C_dl at the OCP. The EIS parameters at elevated potentials indicate that the Pd-Ag alloys should have satisfactory clinical corrosion resistance. The EIS analyses yielded information about in vitro corrosion of these alloys that cannot be obtained from potentiodynamic polarization testing.

The effect of composite PHB coating on the biological properties of a magnesium based alloy

Magnesium alloys have been widely investigated as biodegradable cardiovascular temporal implants due to their better mechanical properties and biocompatibility, but the rapid degradation limited its application. In this study, the anodic oxidation-Cu structure was used to improve the adhesive strength and stability between poly-β-hydroxybutyrate (PHB) and magnesium alloys, and the effects of anodic oxidation magnesium alloys with copper film and PHB film (MACP) on human umbilical vein endothelial cells (HUVECs), blood compatibility and antibacterial properties were investigated in this research. As the result, the MACP structure had a stable structure and better corrosion resistance, and significant antibacterial properties. The coating would not affect the original excellent biocompatibility of the magnesium alloy. It was indicated that MACP was a potential surface modification strategy for vascular stents candidate material.

ICP-MS measurements of elemental release from two palladium alloys into a corrosion testing medium for different solution volumes and agitation conditions

STATEMENT OF PROBLEM

The in vivo release of Pd from palladium alloys into the oral environment and sensitivity reactions by patients has been of concern. However, little information is available about the variation in elemental release from different palladium alloys.

PURPOSE

The purpose of this in vitro study was to compare the elemental release into a corrosion-testing medium from a high-palladium alloy (Freedom Plus, 78Pd-8Cu-5Ga-6In-2Au) and a Pd-Ag alloy (Super Star, 60Pd-28Ag-6In-5Sn) under different conditions.

MATERIAL AND METHODS

Alloys were cast into Ø12×1-mm-thick disks, subjected to simulated porcelain-firing heat treatment, polished, and ultrasonically cleaned in ethanol. Three specimens of each alloy were immersed for 700 hours in a solution for in vitro corrosion testing (ISO Standard 10271) that was maintained at 37 °C. Two solution volumes (125 mL and 250 mL) were used, and the solutions were subjected to either no agitation or agitation. Elemental compositions of the solutions were analyzed by using inductively coupled plasma-mass spectroscopy (ICP-MS). Concentrations of released elements from each alloy for the 2 solution volumes and agitation conditions were compared by using the restricted maximum likelihood estimation method with a 4-way repeated-measures ANOVA, the Satterwhite degrees of freedom method, a lognormal response distribution, and the covariance structure of compound symmetry.

RESULTS

For the 4 combinations of solution volume and agitation conditions, the mean amount of palladium released was 3 orders of magnitude less for the Pd-Ag alloy (0.009 to 0.017 μg/cm² of alloy surface) compared with the Pd-Cu-Ga alloy (17.9 to 28.7 μg/cm²). Larger mean amounts of Sn, Ga, Ag, and In (0.29 to 0.39, 0.57 to 0.83, 0.71 to 1.08, and 0.91 to 1.25 μg/cm², respectively) compared with Pd were released from the Pd-Ag alloy. Smaller amounts of Cu, Ga, and In (4.8 to 9.9, 5.9 to 12.8, and 4.2 to 9.5 μg/cm², respectively) compared with Pd were released from the Pd-Cu-Ga alloy. The Ru released was much lower for the Pd-Ag alloy (0.002 μg/cm²) than the Pd-Cu-Ga alloy (0.032 to 0.053 μg/cm²). Statistically significant differences (P<.001) in elemental release were found for the factors of alloy and element and the alloy×element interaction. Significant differences were found for the solution volume (P=.022), solution volume×element interaction (P=.022), and alloy×solution volume×element interaction (P=.004). No significant effect was found for agitation condition.

CONCLUSIONS

The relative amounts of released elements from each alloy were not proportional to the relative amounts in the composition. The amounts of Pd and Ga released from the Pd-Cu-Ga alloy were consistent with the breakdown of a Pd₂Ga microstructural phase and perhaps some dissolution of the palladium solid solution matrix. Precipitates, rather than the palladium solid solution matrix, appeared to undergo greater dissolution in the Pd-Ag alloy. The Pd-Ag alloy should have lower risk of adverse biological reactions than the Pd-Cu-Ga alloy.