Characterization of the Setting Process in Alginate Impression Materials

¹ Dental School of the London Hospital Medical College, London, England

Using an Atkinson-Nancarrow Viscometer, an index of viscosity for an alginate impression material can be measured, and hence the time for onset of the setting reaction (₁) and the formation of an elastic gel (₂) can be identified by plotting a force-time graph.

A common linear relation between ₁ and ₂ is shown to apply for a number of materials and experimental conditions.

The temperature dependence of ₁ (and hence ₂) obeys an activation energy law [see figure in the PDF file] (l/₁ = B exp (-E/RT). The only parameter that differs from one material to another is B, as might be expected since the same basic reaction is involved in each material. This means that a log – 1/T plot for a number of materials gives a straight line for each material and for each water/powder ratio, all lines having the same slope. Hence data for a wide range of different alginates can be presented in a simple and unified way.