A simple method is described for following changes in viscosity of concentrated aqueous solutions of polycarboxylic acids used in certain dental cements. The difference in behavior over several months between solutions of polyacrylic acid and related polyelectrolytes is discussed.

Acrylates↗

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Conductometric titration of aqueous solutions of polyacrylic acid and its copolymers.

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Acrylates↗

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Zinc polycarboxylate cements: a chemical study of erosion and its relationship to molecular structure.

Experimental results show that the rate of elution of Zn2+ and Mg2+ ions from polycarboxylate cements decrease with the cement's age. This phenomenon is explained by the setting reaction in which these cations are liberated from the oxide powder by an exchange with protons from the polyacid and in this state are vulnerable to water leaching. Subsequently, these cations become bound to the polyanion chain and become more resistant to water leaching. Magnesium ions are more easily hydrolyzed than zinc ions because they are less strongly bound to the polyanion chain. Zinc ions are apparently more strongly bound to a polyacid which is a copolymer of acrylic and itaconic acids, than to the homopolymer of acrylic acid. The pattern of elution of ions differs between the different cements, so that measurements after 24 hours cannot be used to predict long-term durability on a comparative basis. This coupled with the slow but continuous loss of ions makes a 24-hour test of doubtful validity. Polycarboxylate cements absorb water that is present in the matrix in loosely bound and tightly bound forms. The ionization of the polyacid to a polyanion during the course of the reaction apparently creates a demand for water, and the cement where the COOH:C ratio in the polyacid is highest absorbs the most water.

Absorption↗

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Reactions in glass-ionomer cements: IV. Effect of chelating comonomers on setting behavior.

The oscillating rheometer is a valuable instrument for studying the effects of additives on the setting behavior of a cement system. Using this instrument, it was found that certain chelating comonomers, the hydroxycarboxylic acids, could improve the setting characteristics of the glass-ionomer cement system when added to the PAA solution. The acid chelates probably assign the extraction of metal ions from the glass and also tend to hold them in solution, preventing premature ion binding of the polyanion chains. The effect is to increase the rate of hardening without reducing the working time, which may indeed by slightly increased. Tartaric acid, the most effective of the comonomers, can form a chelate bridge between aluminum atoms, and this metal complex probably acts as a flexible bridge structure linking polyanion chains. This mechanism offers some steric advantages over a simple salt bridge.

Acrylic Resins↗

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Reactions in glass ionomer cements: V. Effect of incorporating tartaric acid in the cement liquid.

A description is give of the effect on the ASPA cement reaction of tartaric acid incorporated in the cement liquid. Tartaric acid acts as an accelerator that aids in the extraction of ions from the aluminosilicate glass and facilitates their binding to the polyanion chains. Postgelation hardening is significantly increased. Working time is unaffected possibly because cations are initially present as complexes.

Acrylates↗

PubMedDate not supplied

Glass ionomer cements: chemistry of erosion.

A three-month study of the chemistry of the water erosion of two forms of ASPA cement has been made. The effect of varying cement consistency and cure time was investigated. The results are discussed in terms of the known chemistry and structure of the cement. The erosion behavior is compared to that of silicate, silicophosphate, and zinc polycarboxylate dental cements. The state of absorbed water and the mechanism of erosion is discussed.

Acrylates↗