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Studies of the stability and toxicity of zinc polyacrylate (polycarboxylate) cements (PAZ).

Zinc polycarboxylate cement (PAZ) was shown to actively bond to 45Ca in vitro, with maximum uptake occurring at a Ca+2 concentration of 0.2 mg/ml. When the resultant PAZ-45Ca complex was subsequently incubated in the presence of high levels of unlabeled Ca+2, there was an exchange between the 45Ca bond to the cement and the Ca+2 in solution. When PAZ prepared using 65Zn was incubated with high levels of Ca+2, there was no exchange between the Ca and the 65Zn. 14C-PA failed to be taken up by L-cells in tissue culture, during 16 division cycles. Using radioactive PAZ prepared from 14C-PA, the PA moiety of the cement was shown to be extremely insoluble and stable in vivo.

Acrylates↗

Adhesion of polycarboxylate cements to dental casting alloys.

The adhesive strengths of four commercial polycarboxylate cements to five dental casting alloys were compared with the strength of a conventional zinc phosphate cement. The following results were obtained. (1) The polycarboxylate cements showed adhesion that was four to 12 times greater than that of the zinc phosphate cement to all alloys tested. (2) The adhesive strength of the polycarboxylate cements was greater to the chemically active substitute alloys, such as the copper, nickel-chromium, and silver-tin-zinc alloys. The adhesion of the polycarboxylate cements to the chemically stable gold and silver-palladium alloys was not as great, but was four to six times that of the zinc phosphate cement. (3) The difference in adhesive strength between the brands of polycarboxylate cement was generally slight or statistically insignificant.

Acrylates↗

Reinforced polycarboxylate cements.

Mechanical properties of polycarboxylate cements are greatly improved by incorporation of high modulus fibers such as potassium titanate into acrylic-itaconic acid and acrylic-itaconic-acronitic acid copolymers. Other desirable properties of the cements are not changed by the addition of fibers.

Aconitic Acid↗

Linear dimensional changes during setting of two polycarboxylate cements.

The linear dimensional changes of two polycarboxylate cements have been studied. The measurements were performed on specimens placed on a mercury bath, and were started 3 min after commencing the mix. The specimens were allowed to set at 37 degrees C under various environmental humidity. Specimens from one of the polycarboxylate cements (Durelon), were made using both the universal liquid and the thin liquid meant for cementation. The powder/liquid ratios (P/L) were either 2-5 or 1-5.. Specimens from the second cement (Poly-C), were made using the liquid meant for cementation only with a P/L of 1-5. The dimensional changes of Durelon were dependent on the powder/liquid ratio and the environmental humidity during setting. Under dry conditions this cement showed a maximum contraction of 4-60% after 14 days when a high P/L was used and 6-10% when a low P/L was used. After 1 day under wet conditions no significant differences between cements with high and low P/L were registered, and the mean contraction was 1-10%. The dimensional changes of Poly-C were dependent on the environmental humidity, and after 14 days under dry conditions a maximum contraction of 5-50% was registered and after 1 day under wet conditions a contraction of 0-60%. The contraction of the polycarboxylate cements tested in this study started earlier and were in general more pronounced than that observed for a zinc phosphate cement (Oilo, 1975).

Acrylates↗

Physical properties of some zinc phosphate and polycarboxylate cements.

Several physical properties were measured for two zinc phosphate and three polycarboxylate cements. The specimens were tested in compression 24 h after they had been made. Two series of specimens were examined. In one series the cement powders were given a correct treatment, protected from atmospheric humidity. In the other series the powders were exposed for 1 week to ambient conditions with the temperature varying between 20 degrees and 24 degrees C and the relative humidity between 40% and 59%. The zinc phosphate cements were characterized by high values of modulus of elasticity and by plastic deformations less than 0.2%. The polycarboxylate cements were more flexible and also exhibited large plastic deformations. Compared with the zinc phosphate cements, therefore, the polycarboxylate cements had high values of resilience and toughness. The storing of cement powders exposed to atmospheric humidity for 1 week did not change the measured properties of the polycarboxylate cements. However, both strength and resilience were significantly reduced for one phosphate cement.

Chemical Phenomena↗