Date of Award
Master of Science (MS)
Bradley, Thomas G.
Introduction: The polymerization and acid<–>base reactions in resin<–>modified glass<–>ionomers (RMGI) are thought to compete with and inhibit one another. The objective of this study was to examine the effect of visible light<–>cure (VLC) delay on the polymerization efficiency and orthodontic bond strength of a dual<–>cured RMGI.
Methods: An RMGI light<–>cured immediately, 2.5, 5, or 10 minutes after mixing comprised the experimental groups. Isothermal and dynamic temperature scan differential scanning calorimetry (DSC) analysis of the RMGI was performed to determine extents of VLC polymerization and acid<–>base reaction exotherms. Human premolars (n = 18/group) were bonded with the RMGI. Shear bond strength and adhesive remnant index (ARI) scores were determined.
Results: DSC results showed the 10 minute delay RMGI group experienced significantly (P <0.05) lower VLC polymerization compared to the other groups. Acid<–>base reaction exotherms were undetected in all groups except the 10 minute delay group. No significant differences (P >0.05) were noted among the groups for mean shear bond strength. A chi<–>square test showed no significant difference (P = 0.428) in ARI scores between groups.
Conclusions: Delay in light<–>curing may reduce polymerization efficiency and alter the structure of the RMGI, but orthodontic shear bond strength does not appear to be compromised.