Objective. Several methacrylate/glass ionomer hybrid materials are now
available for clinical use as restorative filling materials. However,
the long-term resistance of these materials to physical degradation i
n the humid oral condition is not known. The objective of this investi
gation was to determine the mechanical properties, e.g., ultimate comp
ressive strength and diametral tensile strength, of several glass iono
mer materials as a function of time after aging in water at oral tempe
rature. Methods. Eight glass ionomer filling materials indicated for r
estorative or core build-up applications were studied. Three conventio
nal glass ionomers, two metal-containing conventional glass ionomers a
nd three methacrylate-modified systems were included in the study. Cur
ed specimens of each were aged in distilled water at 37 degrees C for
24 h, 1 wk, 4 wk, 12 wk, 24 wk and 52 wk. Results. Like the convention
al glass ionomers, the methacrylate-modified glass ionomers of this st
udy, with one exception, did not exhibit a decrease in compressive str
ength, modulus and diametral tensile strength as a result of prolonged
storage in water at oral temperature. Some differences among the vari
ous groups were apparent. The compressive strengths of the conventiona
l glass ionomers were lower than the methacrylate-modified system, exc
ept for one material, Fuji II (GC Dental Corp.), of the former group.
A significant difference in the compressive strength was seen between
the encapsulated and hand-mixed versions of the same commercial brand
product. The compressive modulus was higher and the diametral tensile
strength was lower for the conventional systems indicating that, as a
group, these materials are more brittle than the methacrylate-modified
hybrid ionomers. With the exception of VariGlass VLC (L.D. Caulk), mo
st of the materials studied showed little decrease in mechanical prope
rties after aging in water for 52 wk. Significance. These materials co
uld, therefore, be indicated for use in applications where they are in
contact with oral fluids under physiological conditions.