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

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. 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). 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. 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.