Effects of long-term storage on properties of an alginate impression material

Statement of problem. Storage stability is a critical characteristic for perishable dental materials. Purpose. The purpose of this shelf-life study was to document changes in the properties of an alginate impression material on exposure to various environmental conditions for more than 78 months. Material and methods. Properties measured included recovery from deformation, strain in compression, compressive strength, tear strength, working time, and creep compliance. Results. Results revealed increases in strength and working time and a decrease in recovery from deformation at 30 to 50 months; strength and recovery then remained constant past 6 years, whereas working time and creep compliance decreased. Only the most stressful environmental conditions (heat and humidity) caused spontaneous failure of the material to set. Conclusions. We concluded that, under most storage conditions, properties of the alginate material tested remain within ADA specification limits well past manufacturer's designated shelf life. ADA specifications should require manufacturers to verify that the shelf life of each perishable material is based on valid data. An accelerated aging test was developed to simulate real-time property changes and to assist in evaluating similar materials. (J Prosthet Dent 1997;77:601-6.)