Proportioning effect on physical and chemical properties of polysulfide impression material.

This study investigated the effect of variation in proportioning polysulfide base and catalyst. Light, regular, and heavy-bodied pastes were mixed in linear equivalents of base-to-catalyst proportions of 30/70, 40/60, 50/50, 60/40, and 70/30. Compression set, strain in compression, and consistency tests conformed to the American Dental Association (ADA) Specification 19 guidelines. The amount of solventleachable components and differences in the cross-linked nature of the cured products were studies. Compression set and strain in compression tests met the ADA specification guidelines. Some consistency values fell outside of the ADA specification limits. The leachable content increased with increasing proportions of catalyst, but polymer cross-linking was remarkably similar for all bodied materials tested. Clinicians need not fear a significant property alteration in polysulfide impression material by the differences (within +/- 20% of the manufacturer's suggested lengths) in proportioning the component pastes with "eyeball" estimation as directed in the instructions.