The aim of the present study was to evaluate the effect of delayed light activation and the application of EDTA on bond strength between resin modified glass ionomer and dentin. Thirty permanent sound human posterior teeth were used. The crowns were separated from the roots 1mm below cervical line and then the crowns were cut in a mesio-distal direction to obtain two halves. Samples then were embedded in self cure acrylic resin and then trimmed to create flat dentinal surfaces. Samples were divided in to three groups of 20 each according to light activation (immediate, delayed or without). Each group was subdivided into two subgroups of 10 each according to EDTA application (conditioned or non-conditioned). The restorative material was applied to a cylindrical mold (2 mm diameter and a height of 1mm) fixed on the surfaces of conditioned and non-conditioned samples then subjected to light activation either immediate,
delayed or without. Samples were stored for 24h at 37°C. Shear bond strength testing was done using universal testing machine. Two teeth for each group were prepared for SEM evaluation after being divided longitudinally within the center of the restoration and the interface was examined. The results showed that delaying light activation has significantly decreased shear bond between RMGI and dentin and that the application of EDTA resulted in increase in bond strength for all groups. The lowest shear bond strength was for the conventional type while the highest one was for the immediate light cured RMGI group. The interface as revealed by the SEM showed thicker and longer resin tags in the EDTA preconditioned specimens than without conditioning. It was concluded that the use of EDTA as dentin pre conditioning was beneficial to the bond strength of both RMGI and conventional GI to dentin and that RMGI provides better
dentin bonding as compared to conventional GI.