Depth microhardness of glass ionomer cements.

The purpose of this study was to observe the effect of different conditions of storage on the surface and in the depth of luting glass ionomer cement by measuring microhardness. The hardness of a glass ionomer cement was measured after storage in wet and dry conditions and in an atmosphere of 80% relative humidity, for times up to 1000 h. Storage in distilled water produced a softening effect, but the depth hardness increased progressively. The penetration of the water is a surface phenomenon and does not affect the depth of the cement. However, the cement is vulnerable to moisture to a depth of 600 microns and marginal gaps evolve in the range of 40 to 80 microns when the luting cement at the tooth crown margin is always destroyed.