What is the working time of zinc polycarboxylate cement?
Correct Answer: 3 minutes
Description: Control of Working Time
The working time for polycarboxylate cement is much shorter than that for zinc phosphate cement, approximately 2.5 versus 5 minutes.
The graph shows the relative viscosities and working times of zinc phosphate, polycarboxylate, and GICs as they set.
A cool slab lengthens the working time for zinc carboxylate cement, although it causes the polyacrylic acid to thicken, which hinders mixing.
Refrigerating the powder is useful, because it retards the reaction without raising the viscosity of the liquid.
Polycarboxylate cements are more viscous than a comparable mix of GIC; however, the polycarboxylate mix undergoes thinning at an increased shear rate.
Clinically, this means that rapid spatulation and fast seating will reduce the viscosity of the polycarboxylate cement to ensure complete seating.
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