Resin-modified glass-ionomer (RMGI) acid-base and light polymerization reactions influence one another during early RMGI development. Previous research has shown the thermal degradation of a RMGI with differential scanning calorimetry (DSC) produces a material decomposition endotherm that may serve as a relative indicator of glass-ionomer/resin material character (Abey et al., IADR#33, 2007).
Objectives: To investigate the influence of light-activation on the thermal analysis of a resin-modified glass-ionomer at 30 minutes and 1 day after mixing.
Methods: Fuji II LC capsules (GC America, Alsip, IL) were mixed according to manufacturer instructions, dispensed into aluminum crucibles, and evaluated with DSC (Mettler Toledo, Inc., Columbus, Ohio) using a dynamic scan from 37–600oC at 10oC/min. Two groups were examined: specimens that were immediately light-activated (20 seconds) after mixing and another with no light-activation (dark cure). DSC evaluation was performed 30 minutes or 1 day after mixing and storage at 37oC. Thermograms were analyzed for material degradation endotherms with statistical analysis performed with two-way ANOVA (n=10/group/time).
Results: Two main endothermic degradation peaks were observed. The average and standard deviation values for the high and low temperature endothermic peaks for each group are listed. Capital and small letters denote significant differences (p<0.05) between DSC evaluation time after mixing (RMGI maturation time) and curing mode, respectively.
GROUP | Low Temperature Enthalpy (J/g) | Low Temperature Endotherm (oC) | High Temperature Enthalpy (J/g) | High Temperature Endotherm (oC) | |
30 min | Immediate Light Cure | 20.67±6.90 Ab | 191.08±11.18 Aa | 17.27±7.87 Aa | 405.91±3.09 Ab |
Dark Cure
| 24.21±8.49 Aa | 165.7±11.28 Aa | 9.45±14.88 Ab | 416.39±13.24 Aa | |
1 Day | Immediate Light Cure | 10.82±5.78 Bb | 102.87±5.86 Ba | 14.06±2.08 Aa | 396.70±0.72 Ab |
Dark Cure
| 22.2±11.20 Ba | 136.27±6.31 Ba | 2.31±1.03 Ab | 420.75±4.42 Aa | |
Conclusion: Variable light-activation and RMGI maturation time resulted in differences in RMGI character/structure that were detected with thermal analysis.