Mechanical Properties of Hydrocolloid and Rubber Impression Materials

¹ University of Michigan, School of Dentistry, Ann Arbor, Michigan

The elastic and plastic qualities of alginate gels were determined by measuring the resistance to tearing and the stress-strain properties in compression. The tear strength and compressive strengths were determined as a function of alginate concentration, the time of testing, and the rate of load application. The strain at constant stress as well as the permanent deformation at constant stress and constant strain were determined.

The tear strengths and the compressive strengths were shown to increase with (1) an increase in rate of loading, (2) an increase in the amount of alginate in the mix, and (3) an increase in the time between mixing and testing. The resistance to tearing of the alginates was comparable to agar impression materials but was much lower than those of two mercaptan products.

The strain and permanent deformation measured at a constant stress was decreased when more alginate was used. Variation in the time of testing from 4 to 10 minutes had no significant influence on the strain or permanent deformation measured at constant stress.

The permanent deformation at a fixed strain of 10 to 12 percent was significantly influenced by the change in alginate concentration studied but was not significantly affected by the variation of 4 to 10 minutes in the time of testing.