Microhardness and chemical analysis of high-viscous glass-ionomer cement after 10 years of clinical service as ART restorations

ObjectivesThe aim of this study was to evaluate the Knoop microhardness (KHN) and chemical composition of high-viscous glass-ionomer cement (HVGIC) after 10 years of clinical service.MethodsSix HVGIC samples were cut from 10-year ART restorations. The sections were embedded in acrylic moulds with their longitudinal profile exposed. KHN was determined by performing three sequences of five indentations at 10, 30, 50, 70 and 90 μm of HVGIC outer surface. For the control group (n = 6), HVGIC specimens were stored in distilled water for 24 months. Hardness measurements were taken at days 7, 30, 60, 120, 180, 360, and 720. For chemical analysis using SEM-EDX, 10-year and control specimens were dehydrated and coated with carbon. Data were analysed using T-test and ANOVA/Tukey's test (p < 0.05).ResultsA significant KHN increase was observed in the control group up to the 180-day period. From this point the values stabilized and no more significant differences were found between the 10-year and the control KHN values. No statistical differences were observed amongst the KHN from inner distances compared to the outer surface of the 10-year HVGIC specimens. In one 10-year specimen, SEM-images identified the transformation of HVGIC in an altered layer with no glass filler particles detectable, and raised Ca, K and P contents.ConclusionsKHN values of ten-year HVGIC specimens were similar to the control group values at 180-day storage period. Except for one 10-year specimen in that an altered layer could be seen, chemical composition was similar amongst the depths evaluated.