The application of magnetic resonance microimaging to the visible light curing of dental resins. Part 2. Dynamic imaging by the FLASH-MOVIE pulse sequence

Objectives: To investigate the application of a rapid NMR imaging pulse sequence, FLASH-MOVIE, to the visible light curing of dental restorative materials. Methods: The light guide was applied at one end of a cylindrical specimen of visible light curing unfilled resin and the light directed along the cylinder. During polymerisation an NMR imaging pulse sequence, FLASH-MOVIE, was run at 15 s intervals with a 50 ms repetition time. The image of a 1 mm thick vertical slice was recorded with a (125 mum)(2) pixel size. Results: Images with good contrast were obtained from all resin monomers. The image intensity from the polymer was indistinguishable from the background intensity. Thus, the progress of light activated polymerisation in the material could be followed in real time through a series of up to 16 images. Initially the image intensity increased in the material closest to the light guide, then decreased over time to zero. Concomitant with this fall, a "cure-front" moved through the specimen. Significance: The FLASH-MOVIE NMR pulse sequence applied to microimaging of dental diacrylate resins can be used to obtain a dynamic record of visible light curing. A more refined experimental protocol will be required to apply this unique data to models proposed for this polymerisation mechanism. (C) 2001 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.