A preliminary study of an aluminum-free glass polyalkenoate cement

Abstract

Glass polyalkenoate cements (GPCs) are formed by the reaction of an ion leachable alumino-silicate glass with an aqueous solution of poly (alkenoic acid). Water is used as the reaction medium. An acid-base reaction, occurs, whereby the acid attacks and degrades the glass structure, releasing metal cations which are then chelated by the carboxylate groups and serve to crosslink the polyacid chains. The final cement consists of residual glass particles embedded in a hydrogel polysalt matrix [1]. The setting reaction in GPCs is a continuous process evident by the increase in compressive strength of the cement with aging time [2–5]. GPCs can release clinically beneficial amounts of fluoride [6, 7] and have acceptable handling properties and aesthetics [8, 9] making them suitable as dental restoratives. However, the presence of aluminum in the glass phase of the cements limits orthopaedic applications as research has shown that aluminum ions released from glass polyalkenoate cements can result in defective bone mineralization [10] and as a consequence the ability of these cements to chemically bond to bone may be retarded. There are also concerns over the toxicity of aluminum [11]. An aluminum-free polycarboxylic acid based cement would be of considerable interest in the surgical field. The aluminum ion is believed to play an integral role in the setting process of a GPC and the complete removal of aluminum is likely to hinder cement formation. However, zinc oxide is unusual in that it can act both as a network modifying oxide and as an intermediate oxide [12] in a similar fashion to alumina. This results in ternary systems based on zinc silicates (with the exception of those containing alumina) often having very extensive regions of glass formation. Zinc silicate glasses containing little or no alumina may therefore be suitable for forming polyalkenoate cements and the purpose of this work is to investigate cement formation between such a zinc silicate glass and a series of polyacrylic acids, with the ultimate objective of developing a new range of GPCs that have orthopaedic applications. One glass composition was produced, 0.4SiO2 0.32CaCO3 0.28ZnO. This formulation corresponds to