Лако-красочные материалы — производство

One of the oldest lining materials in use, calcium hydroxide cement still enjoys some popularity in this field, although in a vastly modified form. It has antibacterial properties, is biocompatible, and promotes pulp recovery and regrowth of dentin. In the original form used—namely, as a suspension of calcium hydroxide in water—it yielded cements too weak for acceptable clinical performance. Coapplication of bonding agents such as methyl or carboxymethyl cellulose marginally raised the tensile and compressive strengths to 1 to 2 MPa and 7 to 8 MPa, respectively, and in order to apply the material as a liner under amalgam, an underlay by a different, stronger cement was required. More recent products are of the two-part type, with zinc oxide (typically, 10%) in combination with calcium hydroxide (50%) in one part, and salicylic esters exemplified by 1,3-butylene glycol disalicylate (40%) in the other. Cementation hence involves chelation, as in the more commonly used zinc oxide-eugenol cements discussed in Section II. B.3.

The latest development in the field of calcium hydroxide cements aims at light — activated compositions. The setting reaction in these products is quite different from the chelate formation mechanism of the calcium-zinc salicylate cements insofar as the materi­als harden through light-induced, chemically activated polymerization of dimethacrylate (bis-GMA) and monomethacrylate (HEMA) monomers as coingredients with calcium hydroxide. Although compressive strength values of present-day materials are still quite low (ca. 20 MPa), lining under amalgam is practicable under restricted conditions of cavity geometry. More often, these products are used as liners under silicate — or resin-based fillings. The bonding mode of the calcium hydroxide cements is largely micromechanical.