Micro magnetic resonance imaging of water uptake by glass ionomer cements

The purpose of the present study was: 1) to visualize the water penetration into glass ionomer cement samples prepared in two different setting modes as a function of time, and 2) to assess the potential use of micro magnetic resonance imaging by studying penetration processes.

An encapsulated form of resin-modified glass ionomer cement (Fuji II LC, GC) was used in this study. The mixed cement was syringed into quartz tubes (4 mm ID x 10 mm long). Half of the samples were radially exposed to a light source for 120 s; the other half were allowed to set chemically in a photographic darkroom. One hour after the start of mixing, samples were extruded from the quartz tubes, immediately immersed in distilled water, and stored at 37 degrees C. Eight specimens were prepared with each setting mode and imaged at different times. Micro magnetic resonance imaging was performed on a Bruker Biospec System equipped with micro-imaging utilities. A spin echo technique was used. A small tube containing a mixture of normal and deuterated water was added as a standard to which the signals from the samples were normalized. The average signal, as calculated by the image processing software from each region, was divided by the signal from the standard sample to obtain the normalized intensity. The results were analyzed by a Student's t-test.

After 24 h of immersion, water diffused 1 mm into the chemical-cured material and approximately 0.5 mm in the light-cured samples. After 96 h, the water had reached the center of all chemical-cured samples but not of the light-cured samples. After 192 h, water had reached the center of the cylinders of both groups of samples.

MRI microscopy is a good method for monitoring the water permeability of glass ionomer cements. The technique is nondestructive thus, the process can be followed on the same sample without destroying it. By using some special imaging techniques, refinement of the method will be possible.