ICP-MSによる2種類のパラジウム合金から腐食試験媒体への元素放出の測定（溶液量と撹拌条件を変えた場合）

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

抄録

問題提起:

パラジウム合金から口腔内環境へのPdの生体内放出と患者による過敏反応が懸念されている。しかし、パラジウム合金の違いによる元素放出のばらつきに関する情報はほとんどない。

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.

目的:

本試験の目的は、高パラジウム合金（フリーダム・プラス、78Pd-8Cu-5Ga-6In-2Au）とPd-Ag合金（スーパー・スター、60Pd-28Ag-6In-5Sn）の異なる条件下における腐食試験媒体への元素放出を比較することである。

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.

材料と方法:

合金をØ12×1mm厚の円盤状に鋳造し、模擬磁器焼成熱処理を施した後、研磨し、エタノール中で超音波洗浄した。各合金の試験片3枚を37℃に保たれた試験管内腐食試験用溶液（ISO規格10271）に700時間浸漬した。溶液量は2種類（125 mLと250 mL）を用い、溶液は無撹拌または撹拌した。溶液の元素組成は、誘導結合プラズマ質量分析法（ICP-MS）を用いて分析した。2種類の溶液量と撹拌条件における各合金からの放出元素濃度を、4元配置反復測定ANOVA、サターホワイト自由度法、対数正規応答分布、化合物対称性の共分散構造を用いた制限最尤推定法を用いて比較した。

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.

結果:

溶液量と撹拌条件の4つの組み合わせにおいて、放出されたパラジウムの平均量は、Pd-Cu-Ga合金（17.9～28.7μg/cm）に比べて、Pd-Ag合金（合金表面0.009～0.017μg/cm）では3桁少なかった。Pd-Ag合金からは、Pdに比べてSn、Ga、Ag、Inの平均量が多く（それぞれ0.29～0.39、0.57～0.83、0.71～1.08、0.91～1.25μg/cm）放出された。Pd-Cu-Ga合金からは、Pdに比べて少量のCu、Ga、In（それぞれ4.8～9.9、5.9～12.8、4.2～9.5μg/cm）が放出された。放出されたRuはPd-Cu-Ga合金（0.032～0.053μg/cm）よりPd-Ag合金（0.002μg/cm）の方がはるかに低かった。元素放出における統計的に有意な差（P<.001）は、合金と元素の因子および合金×元素の相互作用で認められた。溶液量（P=.022）、溶液量×元素の相互作用（P=.022）、合金×溶液量×元素の相互作用（P=.004）で有意差が認められた。攪拌条件では有意な効果は認められなかった。

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/cm of alloy surface) compared with the Pd-Cu-Ga alloy (17.9 to 28.7 μg/cm). 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/cm, 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/cm, 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/cm) than the Pd-Cu-Ga alloy (0.032 to 0.053 μg/cm). 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.

結論:

各合金から放出された元素の相対量は、組成中の相対量に比例しなかった。Pd-Cu-Ga合金から放出されたPdとGaの量は、PdGa微細構造相の破壊と、おそらくパラジウム固溶体マトリックスの溶解と一致した。Pd-Ag合金では、パラジウム固溶体マトリックスではなく、析出物がより大きな溶解を受けたように見えた。Pd-Ag合金は、Pd-Cu-Ga合金よりも生物学的な有害反応のリスクが低いはずである。

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 PdGa 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.