歯科用ポリカルボキシレートセメント硬化体の侵食過程

抄録

Erosion process of the zinc polycarboxylate cement in various acid solutions was investigated by means of determination of Zn and Mg leached from the cement and SEM observation of the surface structure. The amount of species leached from the cement increased with increasing dissociation constant of the acid, that is, with decreasing pH of the solution. Partial neutralization of the acid decreased the amounts of Zn and Mg. When the degree of neutralization (=equivalent of NaOH added/equivalent of the acid originally present) reached 1, the amount leached was almost negligible. However, in the acids which formed stable complexes with Zn and Mg, certain amounts of Zn and Mg were released from the cement. Especially with EDTA which formed much stable complexes, the amount leached was independent of the degree of neutralization and showed high value. Erosion of the cement in the acid solutions consisted of two competitive processes, that is, dissolution of the unreacted ZnO particles and erosion of the matrix. The preference of these two processes depends on the dissociation constants of the acids and the formation constants of the complexes between the acids and Zn or Mg. The former occurs preferentially at a lower degree of neutralization. The latter also proceeds in strong acids such as HCl or in acids forming stable complexes such as citric acid and EDTA. With increasing degree of neutralization, erosion of the matrix occurs exclusively with ZnO particles taken off the cement in the latter two acids.