Effect of Light-Cure Initiation Time on Polymerization and Orthodontic Bond Strength with a Resin-Modified Glass-Ionomer

Introduction: The polymerization and acid\u3c–\u3ebase reactions in resin\u3c–\u3emodified glass\u3c–\u3eionomers (RMGI) are thought to compete with and inhibit one another. The objective of this study was to examine the effect of visible light\u3c–\u3ecure (VLC) delay on the polymerization efficiency and orthodontic bond strength of a dual\u3c–\u3ecured RMGI. Methods: An RMGI light\u3c–\u3ecured 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\u3c–\u3ebase 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 \u3c0.05) lower VLC polymerization compared to the other groups. Acid\u3c–\u3ebase reaction exotherms were undetected in all groups except the 10 minute delay group. No significant differences (P \u3e0.05) were noted among the groups for mean shear bond strength. A chi\u3c–\u3esquare test showed no significant difference (P = 0.428) in ARI scores between groups. Conclusions: Delay in light\u3c–\u3ecuring may reduce polymerization efficiency and alter the structure of the RMGI, but orthodontic shear bond strength does not appear to be compromised