Effect of powder/liquid ratio on the clinical and laboratory performance of resin-modified glass-ionomers

Objectives: To compare the effects of powder/liquid (P/L) ratio and surface wetness on retention of adhesive Class V restorations. Methods: One-hundred and six Fuji II LC restorations were placed at two clinical trial sites. In the ‘high-dry’ group (Site A), Fuji II LC was mixed at a P/L ratio of 3.0 and applied to dentine that was visibly dry, but not desiccated. In the ‘low-wet’ group (Site B), Fuji II LC was mixed at a P/L ratio of 2.25 and applied to dentine that was glisteningly moist. The restorations were evaluated at baseline, 1 and 2 years at both sites, and at 3 years at one site. The P/L ratio effects on viscosity and wetting were evaluated in vitro by determining the film thickness possible at different ratios. Results: At 2 years the retention levels at the two sites differed significantly (p ≤ 0.1). Site B (‘low-wet’ group) exhibited 100% retention, and Site A (‘high-dry’ group) exhibited 78% retention. At 3 years Site A exhibited 74% retention, and nine of the 12 retention failures occurred in patients 65 years and older. Laboratory measurements demonstrated that the viscosity of ‘low-wet’ mixtures permitted film thicknesses that were one-half those of the ‘high-dry’ group. Conclusions: The study demonstrated that a higher powder/liquid ratio and a drier dentine surface compromised wetting by a resin-modified glass-ionomer resulting in a decline in retention from baseline to 3 years. This study suggests that the dentine surface should be kept hydrated to promote bonding, and that the powder/liquid ratio should be low enough to create low-viscosity mixtures which promote wetting. In the ‘high-dry’ dentine group there was still 74% retention at 3 years, indicating that factors other than wetting affect retention.