Bond strength and interface micromorphology of an improved resin-modified glass ionomer cement

To evaluate the influence of surface treatment with 20% polyacrylic acid containing 3% aluminum chloride (AlCl3) on the shear bond strength of an improved resin-modified glass ionomer cement to enamel and dentin, and to analyze the micromorphology of the cement-tooth interface.

Flat enamel and dentin surfaces of bovine incisors were ground up with sequentially finer abrasives to 1000-grit silicon carbide paper. Each surface was treated with 10% polyacrylic acid (Dentin Conditioner: DC) for 20 seconds or with 20% polyacrylic acid containing 3% aluminum chloride (Cavity Conditioner: CC) for 10 seconds, rinsed, and gently air-dried. A resin-modified glass ionomer cement (Fuji II LC) and its improved version (Fuji II LC-I) were applied to the tooth substrate, and bond strengths measured at periods of 5 minutes, 1 day, and 1 week after light curing. As a control, the resin-modified glass ionomer cements were applied to untreated surfaces and were tested at 1 day. To evaluate the interface micromorphology, specimens were prepared following the adhesive-sandwich technique, cut in equal halves, and observed under a scanning electron microscope (SEM). Additionally, in order to observe the effect of surface pre-treatment of each conditioner on dentin, pre-treated dentin disks were freeze-dried, fractured, and the morphology of the treated and fractured surfaces were observed.

Shear bond strength of CC+ Fuji II LC-I to enamel was significantly higher than that of DC+ Fuji II LC at 1 day and 1 week (P < 0.0001). As for dentin, the improved system showed significantly higher bond strength at 5 minutes after light curing (P < 0.001), but bond strengths were not statistically different at 1 day and 1 week. Fracture patterns, examined with a stereomicroscope, were mixed adhesive/cohesive within the cement for all groups. Interface micromorphology, observed with an SEM, suggested the formation of a resin-rich layer and an indistinct zone between the resin-modified glass ionomer cements and the underlying dentin.