Effect of Heat Activation on Setting Times of Glass Ionomers

Objectives: No published data exist to explain the effect of heat activation on the setting times of various glass ionomer formulations. Through incremental heat activation, this study evaluated the change in setting time of commonly used glass ionomer restoratives. Methods: According to American Dental Association standards, this study compared heat activated setting times for Fuji IX GP (hand mix, GC Corporation), Fuji IX GP Fast and Fuji Triage™ (auto-mix, GC Corporation) and Ketac®-Fil and Ketac™Molar (auto-mix, 3M ESPE). Standardized root caries preparations were made in extracted human molar teeth, the preparations were restored with the test samples, and heat activation was delivered via halogen curing light for 0, 20, 40, and 60 s. Setting times were recorded and the data analyzed by two-way ANOVA and All Pairwise Multiple Comparisons (Student-Newman-Keuls). Results: 1) All samples demonstrated significant reduction in setting times when heat activated for at least 40 s (p<0.05); 2) Ketac™Molar and Fuji IX GP showed decreased setting times at 20 s of heat activation (p<0.05); 3) Fuji IX GP Fast and Ketac®-Fil demonstrated decreased setting times at 40 s (p<0.05); 4) Fuji Triage™ showed significant reduction of set time at all heat activation intervals (p<0.05); 5) The magnitude of set time reduction for all samples was at least 35.0% (range 35.0-51.0) after 40 s of heat activation. Conclusions: These data demonstrate that heat activation of glass ionomer restorative materials may significantly reduce the setting time. The magnitude of set time reduction may result in significantly less clinical time required for intraoral placement of these restorations.