Resin cure determination by polymerization shrinkage

Objectives. This study was designed to develop a methodology that would measure the monomer conversion of dental restorative resins without the use of an infrared spectrometer. Methods. Specimens were prepared from heat-cured TEGDMA/MMA copolymers consisting of 0,20,40,60, 80 and 100 mole% TEGDMA. The pre- and post-cure volumes of bar-shaped specimens (45 × 7 × 1 mm) and thin films were measured. The cure of the thin specimens was determined using changes in resin volume as well as by an infrared spectroscopic method. The cure of thin specimens of a commercially available unfilled bonding resin was also determined using the shrinkage method and by conventional infrared spectroscopic methods. Results. There was no difference (p = 0.0617) between cure values of the commercial resin using either conventional IR methods or the shrinkage methods. For each copolymer combination of thin films, there was also no significant difference in the extent of cure between the IR method used and the shrinkage method presented (lowest p-value 0.29). The cure of TEGDMA/MMA copolymer bar specimens demonstrated a decreasing trend of cure with increasing proportion of TEGDMA, and had cure values which were similar to others reported in the literature. Significance. The evidence from this study demonstrated that the specimen volume method can be used to determine the extent of resin cure of thin film or bulk resin specimens. This method represents an easily performed procedure that can be used by all investigators without expensive equipment.