Abstract
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.
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Article info
Publication history
Published online: February 14, 2021
Footnotes
Supported by NIDCR grant DE10147.
Identification
Copyright
© 2021 by the Editorial Council for the Journal of Prosthetic Dentistry.
