LONG-TERM MECHANICAL-PROPERTIES OF GLASS IONOMERS

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.