effect of acid pre‑conditioning and/or delayed light irradiation on enamel bond strength of three resin‑modified glass ionomers

background: polymerization of resin‑modified glass‑ionomers (rmgis) is mediated through two competing mechanisms: an acid‑base reaction and a light‑dependent resin polymerization. furthermore, pre‑conditioning with acid has resulted in an increase in enamel bond strength of some rmgis. this in vitro study evaluated the effect of pre‑conditioning and/or delayed irradiation on bond strength of three rmgis to enamel. materials and methods: in this in vitro study, 144 flat enamel surfaces of human molars were ground using consecutively finer abrasives up to 600‑grit silicon carbide paper. each surface was rinsed and gently air‑dried ( n = 12). the rmgis (fuji ii lc improved; ionolux and vitremer) were bonded to enamel surfaces using the following protocols: groups 1: based on manufacturers’ instructions; groups 2: pre‑conditioning with phosphoric acid for 30 s; groups 3: a 2‑min delay in irradiation; groups 4: pre‑conditioning with acid for 30 s plus a 2‑min delay in light activation. after 24‑h storage at 37°c and 500 rounds of thermocycling, the samples underwent shear bond strength (sbs) test. data was analyzed with 3‑way anova and tukey hsd test (α =0.05). results: there were significant differences between the study groups ( p < 0.001). acid‑pre‑conditioning increased fuji ii lc sbs values; it significantly decreased sbs values of vitremer but had no effect on sbs values of ionolux. ionolux and vitremer exhibited decreased enamel bond strength after a delay in light activation ( p < 0.05). a 2‑min delay in light activation combined with acid pre‑conditioning increased rmgi sbs values only for fuji ii lc. conclusion: within the limitations of the present study, the effect of acid pre‑conditioning, delaying irradiation and both on enamel bond strength of rmgis was material‑dependent. further investigations are recommended. key words: acid pre‑conditioning, bond strength, delayed irradiation, enamel, resin‑modified glass‑ionomer