MICRO MAGNETIC-RESONANCE-IMAGING OF WATER-UPTAKE BY GLASS-IONOMER CEMENTS

Objectives: The purpose of the present study was: 1) to visualize the water penetration into glass ionomer cement samples prepared in two di fferent setting modes as a function of time, and 2) to assess the pote ntial use of micro magnetic resonance imaging by studying penetration processes. Methods: An encapsulated form of resin-modified glass ionom er cement (Fuji II LC, GC) was used in this study. The mixed cement wa s syringed into quartz tubes (4 mm ID x 10 mm long). Half of the sampl es were radially exposed to a light source for 120 s; the other half w ere allowed to set chemically in a photographic darkroom. One hour aft er the start of mixing, samples were extruded from the quartz tubes, i mmediately immersed in distilled water, and stored at 37 degrees C. Ei ght specimens were prepared with each setting mode and imaged at diffe rent times, Micro magnetic resonance imaging was performed on a Bruker Biospec System equipped with micro-imaging utilities. A spin echo tec hnique was used. A small tube containing a mixture of normal and deute rated water was added as a standard to which the signals from the samp les were normalized. The average signal, as calculated by the image pr ocessing 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. Results: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 c enter 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 g roups of samples. Significance: MRI microscopy is a good method for mo nitoring the water permeability of glass ionomer cements. The techniqu e is nondestructive thus, the process can be followed on the same samp le without destroying it. By using some special imaging techniques, re finement of the method will be possible.