How fast are your alginate impressions cast?

As the authors of this very interesting paper observe, dental practitioners have been taught for decades that irreversible hydrocolloid impressions (alginate) should be poured as soon as possible, ideally within 12 minutes, to ensure dimensional stability. In this quite simple experiment, two different alginate materials were used to take an unspecified number of impressions of a modified resin model. These were taken using the exact measurement of materials specified by the manufacturers. The impressions were either poured immediately or stored, again according to the manufacturer's instructions, by wrapping the impression in a paper towel dampened with 12 ml tap water and sealing them in plastic zipper storage bags. A number of impressions was poured each day for the following five days.

The resultant gypsum casts were analysed by measuring key points and comparing these measurements with the master model to assess the dimensional stability of the alginate impression material.

Although dimensional changes were recorded, these were not deemed to be clinically significant and none was found to exceed the parameter initially laid down of 0.50% dimensional change. At the end of five days no significant differences were found between the casts poured at the six time intervals, or between the two different materials.