Competition Between Acid-base and Polymerization Reactions in a Resin-modified Glass-ionomer

Resin-modified glass-ionomers (RMGI) set by at least two mechanisms and each is dependent upon reactant diffusion prior to gelation.  The kinetics and extent of each setting reaction/mechanism may rely on and/or compete with the other.  Objectives: To investigate possible RMGI setting reaction interactions using differential scanning calorimetry (DSC) by varying visible light activation (VLC) initiation times after mixing. Methods:  GC Fuji II LC was mixed per manufacturer's instructions, placed in an aluminum crucible, and transferred to a DSC at 37^oC with VLC (20 seconds) occurring immediately or at 5 or 10 minutes after mixing.  Another group (Dark cure) was evaluated without VLC.  The VLC polymerization and/or acid-base reaction exotherms were monitored for 30 minutes followed by a forward and reverse DSC dynamic scan between 37 and 240^oC.  The scan produced an endotherm that served as a relative indicator of glass-ionomer/resin material character.  Finally, a 15 minute 37^oC isothermal was conducted to determine VLC thermal energy input.  Results were analyzed with ANOVA/Scheffe (a=.05). Results:   The mean and standard deviation for each group/parameter are listed (n=10).  Within each parameter, different letters denote significant (p<0.05) differences exist.

As time allowed for the acid-base components to react increased, the extent of VLC reaction exotherm decreased.  Conversely, dynamic DSC data suggest earlier beginning times of light polymerization may limit the acid-base reaction. Conclusion:   Results indicate RMGI acid-base and light polymerization reactions compete and possibly inhibit one another during early RMGI development.