Comparing Polymerization Shrinkage Measurement Methods for Universal Shade Flowable Resin-Based Composites

Universal shade flowable composites have been introduced to mimic tooth structure with reduced color mismatch and reduced chair time and cost. However, the polymerization shrinkage of resin material may lead to sensitivity and restoration failure. The purpose of this study was to compare the polymerization shrinkage of recently introduced universal shade flowable resin-based composites using both wet and dry density methods. Using two measurement methods, ISO 17304 (wet method) and a gas displacement pycnometry system (dry method), the density of the unpolymerized and the polymerized RBCs were measured, and the polymerization shrinkage was calculated from the density difference. Scanning electron microscopy was used to visualize filler particles. The polymerization shrinkage showed significant differences between many materials. In particular, Bulk Base HARD II Medium Flow showed significantly lower polymerization shrinkage than all the other materials. Shrinkages measured by different methods were significantly different in all cases. The wet method measured a smaller shrinkage than the dry method in most cases, but the shrinkage measured for Gracefil LoFlow was larger with the wet method. Shrinkage between universal shade flowable resin-based composites significantly varied based on both material and measurement method. The polymerization shrinkage of resin-based composites is an important factor in biomimetic clinical dentistry, and work must be conducted to measure it accurately and with more standardization.