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 by manufacturers routinely utilised in clinical mixes. Encapsulation ensures the recommended powder to liquid mixing ratio is employed clinically. The aim was to investigate if the in-vitro wear resistance of encapsulated GI restoratives was improved compared with their hand-mixed equivalents prepared with the mixing ratios routinely employed clinically. Methods: The powder contents of six hand-mixed GI restoratives were reduced from that recommended (100%) in 10% increments to 50% and mixed with a constant weight of liquid. The encapsulated equivalents were mechanically mixed in a Rotomix¢â mixing machine. The in-vitro wear resistance testing of eight disc-shaped specimens (15 mm diameter, 1.7 mm thickness) per group was conducted using the OHSU oral wear simulator which imparted a 20 N abrasion force and 90 N attrition force for 50,000 cycles at 1 Hz. The total wear depth and total volumetric wear of each wear facet was analysed using an optical profilometer and the data analysed using a one-way analysis of variance (ANOVA) and Tukey's test comparisons (P<0.05). Results: A progressive increase in the mean total wear depth and mean total volumetric wear was identified as the GI powder content was reduced. The situation was further exacerbated for an anhydrous GI restorative at ≤80% of the recommended powder content. In general, the mean total wear depth and mean total volumetric wear of the encapsulated GI restoratives were significantly reduced (P<0.05) compared with the hand-mixed equivalents prepared with powder contents of ≤80%. Conclusions: The in-vitro wear resistance of GI restoratives hand-mixed utilising the powder to liquid mixing ratios routinely encountered clinically were inadequate. Encapsulated GI restoratives provide a solution to the operator-induced variability associated with hand-mixing.