Effect of surface coating on water migration into resin-modified glass ionomer cements: a magnetic resonance micro-imaging study.

Magnetic resonance micro-imaging was applied to study water diffusion into resin-modified glass ionomer cement restoration and to evaluate the effect of surface coating over restoration. Two cavities were prepared on the labial surface of extracted teeth and restored with resin-modified glass ionomer cement; one was protected with surface coating and the other was not. Immediately after restoration, the teeth were immersed in water. Progress of water diffusion into restorations was monitored by T(1) weighted spin-echo MRI at one-day intervals after the start of immersion. To quantify the water diffusion, a model was developed and compared with imaging data. Best fit yielded an effective water diffusion coefficient D = (2.3 +/- 0.4) 10(-12) m(2)/sec. Experimental results demonstrated that surface coating protects the dental cement against water intrusion from the surface of the restoration which faces the oral cavity. Such coating, however, does not prevent water penetration from the dentine side.