| 摘要 |
A preparation for taking dental impressions and to be prepared for use by mixing it with water, comprises a colloid, a metal salt, and alkaline component which when the preparation is mixed with water renders the preparation alkaline so that the metal salt is initially substantially insoluble in the water and incapable of reacting with the colloid, and a slow acting acidifying component which causes the alkaline preparation to assume a neutral or slightly acid pH value so that the metal salt dissolves in the water and reacts with the colloid to form a resilient gel, the acidifying component being in stoichiometric excess with respect to the alkaline component. The metal salt may be a carbonate or silicate of lead, barium, strontium or calcium. The colloid may be a water soluble alginate, pectate or salt of carboxymethyl-cellulose. The acidifying component may be a weak acid (acetic acid), a salt derived from a weak base and a strong acid, an organic or inorganic ester, an organic or inorganic acid anhydride (molybdic or tungstic acid anhydride), a silicofluoride, a titanofluoride or a zirconofluoride. The alkaline component may be sodium hydroxide or alkali metal silicate, aluminate or zincate. The preparation may include colour change indicators e.g. phenolphthalein and thymolphthalein. In the examples the preparations comprise (1) diatomaceous earth, lead silicate, sodium alginate, sodium silicofluoride and sodium hydroxide; (2) diatomaceous earth, lead silicate, sodium alginate, sodium silicate and sodium silicofluoride; (3) diatomaceous earth, barium carbonate, sodium alginate, sodium carbonate, sodium silicate and sodium silicofluoride; (4) diatomaceous earth, sodium alginate, lead silicate, sodium silicate, sodium silicofluoride, potassium silicofluoride, thymolphthalein and phenolphthalein. |
