Studies on Soluble Elements and Solubility of Dental Cement (1): Solubilities of Zinc Phosphate Cement, Carboxylate Cement and Silicate Cement in the Distilled Water

1. Solubility of zinc phosphate cement The experimental results show that the solubility of any kind of cement soaked for a day or 7 in the distilled water shows comparatively a small value. That is, as shown in Figs. 8 and 9, the solubility of Zn of P1, P2 and P3 soaked for a day shows around 4 fig/cm2, and when soaked for 7 days, it shows 4.1-5.8 μg/cm2. Mg shows 1.8-3.9 μg/cm2, and Ca, a small value. Especially in the case of P3, soaked for a day, the total solubility of Zn, Mg and Ca shows a preferable value, approximately 6.3 pg/cm2. The same tendency can be seen in the 7-day soaking case. But, in comparison with the analyzed values of powder, it is proved that the solubility of Mg is very large, as compared with that of Zn. For instance, the P3 cement powder has ZnO, 90.9% and MgO 8.0%, that is, MgO is approximately one ninth of ZnO in content. But, the solubility of Mg, when soaked for 7 days, shows a large value. The fact tells that Mg in the set product of cement is more soluble than Zn. Let's examine MgO : it is considered that MgO reacts with H3PO4 to form Mg (H2PO4) 2, which finally forms Mg3 (PO4) 2 through MgHPO4. The solubility product, therefore, is considered to be MgHPO4 or Mg3 (PO4) 2. But from the fact that H3PO4 in the solution has not been identified even by the phosphorus molybdate method, it is considered that the solubility of Zn and Mg are mainly due to the elution of these unreacted oxides. Again, the comparison of the solubility of P1, P2 and P3 proves that the solubility of Zn, Mg and Ca in P3 show smaller values. But the comparison of their powder and liquid composition showing small difference in components, cannot make out the difference in solubility. The presumption is that P3 cement shows low solubility because of its comparatively preferable reactivity. 2. Solubility of carboxylate cement The solubility of carboxylate cement in the distilled water (Figs. 10 & 11) is as follows : The solubility of Zn of C., and C2 soaked for a day is less than 1.3 μg/cm2, and 2.3 μg/cm2 in the 7-day soaking case. Ca shows a very small value in any case of cement. But the solubility of Mg is comparatively large, 1.4-2.9 μg/cm2 in a day soaking and 21.0-25.0 μg/cm2 in 7-day soaking, which cannot be explained from the powder composition : according to Table 1, this kind of cement contains MgO, one ninth-tenth of ZnO like zinc phosphate cement, and the above-mentioned phenomenon is hard to understand from the componential viewpoint. Again, th