Glass-ionomer restoratives – do encapsulated materials offer increased performance
Objectives: Glass-ionomer (GI) restoratives are susceptible to operator induced variability on hand-mixing with powder contents of half that recommended being used in clinical mixes. Encapsulation ensures the recommended powder to liquid mixing ratio is employed clinically. The aim was to investigate if encapsulated GIs perform more favourably in terms of mean compressive fracture strength and mean elastic modulus than their hand-mixed equivalents prepared with mixing ratios routinely employed clinically. Methods: The powder contents of six hand-mixed GI restoratives were reduced from that recommended (100%) to 90, 80, 70, 60 and 50% and mixed with a constant weight of liquid. The encapsulated equivalents were mechanically mixed in a Rotomix™ mixing machine. The 24 h mean compressive fracture strengths and mean elastic moduli were determined for groups of 30 cylindrical specimens (6 mm height, 4 mm diameter) and the data analysed using a one-way analysis of variance (ANOVA) and Tukey’s test comparisons at P<0.05. Results: Decreasing the GI powder content resulted in a deterioration of the mean compressive fracture strengths and the mean elastic moduli. In general, the mean compressive fracture strength (134MPa) and mean elastic modulus (4.0GPa) of the encapsulated GI restoratives were significantly increased (P<0.05) compared with their hand-mixed equivalents prepared with ≤80% of the recommended powder content (106MPa and 3.6GPa, respectively). ConclusionEncapsulated GI restoratives offer a solution to operator induced variability associated with hand-mixing. The use of the intrinsic material property (elastic modulus) offers a further tool to the dental materials scientist rather than relying on a non-intrinsic material property (compressive fracture strength).