Influence of a Nanofilled Coating on Physical Properties of Glassionomercements

Objectives: To assess the time-dependent fracture toughness, acid erosion and translucency of the glass ionomer cement (GIC) like restorative Equia in comparison to three conventional uncoated GICs.

Methods: The materials Equia (EQ, GC), Chemfil Rock (CR, Dentsply), Ketac Molar (KM, 3MESPE), and Riva SC (RS, SDI) were selected. Fracture toughness (FT) was measured using the SENB (single-edge-notched-bending) method. Bars with dimensions of 25x2x2 mm (n=15) were produced and stored for 3h, 24h, and 21d in 100% humidity at 37°C. Sharp notches were cut into the bars using a saw blade and a razor blade. The actual notch depths were measured after fracture under a light microscope. Fracture loads were recorded in a universal testing machine and statistically analyzed using two-way ANOVA. Acid erosion (AE) was tested according to ISO 9917 in a lactic acid solution at pH=2.74. Specimen cylinders (5x2mm, n=5) were fabricated from the GICs. The dimensional changes relative to the mold surface before and after soaking for 24h in the erosion solution were measured using a calliper. The data were analyzed by one-way ANOVA. Translucency (TR) was measured qualitatively from specimen discs (15x1 mm) in front of a grey scale line raster. Photographs were taken after 24h and 21d storage in 37°C distilled water.

Results: [Mean (SD)], same letters indicate homogenous subsets.

Material	FT3h [MPam0.5]	FT24h [MPam0.5]	FT21d [MPam0.5]	AE [µm]
EQ	0.47(0.13)b,c	0.56(0.04)c,d	0.63(0.13)d	0.028(0.005)A
CR	0.44(0.06)b	0.55(0.06)c	0.57(0.04)c,d	0.093(0.007)
KM	0.34(0.04)a	0.50(0.09)b	0.53(0.09)c	0.036(0.004)A
RS	-	-	-	0.067(0.007)

Conclusions: FT was found to be improved for EQ at all storage periods due to protective crack sealing with the system varnish. Resistance against AE was best for EQ due to the resin coating layer. Improved optical performance in terms of TR was qualitatively shown for EQ.