The influence of poly(acrylic acid) molar mass on the properties of polyalkenoate cements formed from zinc oxide/apatite mixtures

The influence of poly(acrylic acid) molar mass was investigated on cements formed from zinc oxide-apatite mixtures at three aging times; one, seven an d 28 days. Cements based on both hydroxyapatite and fluorapatite were inves tigated. The compressive strength, un-notched fracture strength and fractur e toughness increased markedly with poly(acrylic acid) molar mass. The frac ture toughness and un-notched fracture strength increased with aging time f or the two highest molar mass cements, but decreased with time for the two lowest molar mass cements. The greater chain entanglement density present i n the higher molar mass cements is thought to contribute significantly to t he cement stability in addition to the crosslinking of the polyacrylate cha ins by calcium and zinc ions. Substitution of hydroxyapatite by fluorapatite had no significant influence on the mechanical properties of the cements at aging times longer than one day. (C) 2000 Kluwer Academic Publishers.