Linear dimensional change during setting of a zinc phosphate cement.

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Abstract
A method for studying the linear dimensional changes of dental cements during setting has been described. The measurements started 3 min after commencing the mix with specimens placed on a mercury bath. Measurements were performed at 37 degrees C and under various environmental humidity. The specimens were made of a fine grain zinc phosphate cement with high powder/liquid ratio (3/1:g/ml) and low powder/liquid ratio (2/1:g/ml), and the measurements showed that the cement contracted during setting under both wet and dry conditions. Under wet conditions cements with both high and low powder/liquid ratio showed the same contraction, with 0-43% after 30 min reaching a maximum of 0-66% after 1 day. Under dry conditions the contraction was more pronounced, and somewhat dependent on the powder/liquid ratio. The cement with the high powder/liquid ratio showed 1-33% contraction after 30 min with a maximum of 3-83% after 7 days, whereas the corresponding values for cement with low powder/liquid ratio were 0-79% and 4-76%.