Changes in properties of nonaqueous elastomeric impression materials after storage of components.

STATEMENT OF PROBLEM Storage stability, or shelf life, is a critical property of perishable dental materials. PURPOSE The purpose of this investigation was to document changes in the properties of nonaqueous elastomeric impression materials over time and on exposure to various environmental conditions. MATERIAL AND METHODS Materials investigated included a polyether impression material, a polysulfide material (light, regular, and heavy consistencies), and an addition-reaction silicone material (light, regular, heavy, and putty consistencies). Tests included viscosity of individual pastes, elastic recovery, working and setting times, strain in compression, dimensional change, creep compliance, and tear energy. Means and standard deviations were calculated for each test interval. Statistical analysis included 2-way ANOVA (variables: time and storage condition) and comparison to baseline values using 1-way ANOVA (variable: time) and Scheffe's multiple comparison test (P < or = 0.05) within each material, consistency, and test. RESULTS Results over 72 months revealed changes in viscosity, working/setting times, elastic recovery, and creep compliance. Separation of components was seen with polysulfide and addition silicone materials. Some batches of polysulfide base paste and polyether reactor paste solidified in the tube. CONCLUSION Most batches of the materials and consistencies tested remained efficacious well past their designated shelf lives under a variety of storage and use conditions. Data for the addition-reaction silicone impression material changed little during the 72-month testing period; thus, the material may be considered relatively storage stable. Creep compliance was the most precise storage-stability indicator. The storage stability of perishable materials should be addressed in American Dental Association Specifications.