The purpose of this study was to compare the effects of thermocycling on the change of Vickers hardness of four resin-modified glass ionomers depending on material types and shades. A conventional glass ionomer and a resin composite material were used as controls. Disk specimens were prepared and polished and Vickers hardness gas measured. _After thermocycling in 5--55 C distilled water for 1,000 and 2,000 cycles, the Vickers hardness as measured: The results were analyzed by the type of materials, and the shade of the materials in the same material, The following results were obtained.
1. The Vickers hardness numbers of Z10 group were statistically higher than those of resin >modified glass ionomers regardless of the thermocycling(p<0.05), and those of conventional type H glass ionomers were significantly lower than `all the other groups(p<0.05).
2. The increase ratio of the Vickers hardness of VGL group was significantly higher than those of other groups up to thermocychng for 1,000 cycles(p<0.05), and the Vickers hardness of Z10 group decreased more than 10 %. The increase ratio of Vickers hardness of Z10 and FJT group was significantly higher than those of the other groups ; during thermocyling from 1,000, to 2,000 cycles(p<0.05). ` --
3. Comparing the Vickers hardness of before-thermocycling and after-2,000 thermocycling, the Vickers hardness numbers of FJT, VGL and FLC group increased by 11--21 % after thermocycling, and those of DET, Z"() and VTM group decreased by 51 % after thermocyclig.
4. The tendency of microhardness change was different depending on the shade of materials, but there was no clear trend.
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