Properties evaluation of silorane, low-shrinkage, non-flowable and flowable resin-based composites in dentistry

Purpose: This study tested the null hypothesis that different classes of direct restorative dental materials (silorane-based resin, low-shrinkage and conventional (non-flowable and flowable) resin-based composite (RBC)) do not differ from each other with regard to polymerization shrinkage, depth of cure, or microhardness. Methods: 140 RBC samples were fabricated and tested by one calibrated operator. Polymerization shrinkage was measured using a gas pycnometer both before and immediately after curing with 36 J/cm² light energy density. Depth of cure was determined, using a penetrometer and the Knoop microhardness was tested from the top surface to a depth of 5 mm. Results: Considering polymerization shrinkage, the authors found significant differences (p<0,05) between different materials: non-flowable RBCs showed lower values, compared to flowable RBCs, with the silorane-based resin presenting the smallest shrinkage. The low shrinkage flowable composite performed similarly to non-flowable, with significant statistical differences compared to the two other flowable RBCs. Regarding to depth of cure, low-shrinkage flowable RBC were most effective compared to other groups. Microhardness was generally higher for the non-flowable vs. flowable RBCs (p<0.05). However, the values for low-shrinkage flowable did not differ significantly from those of non-flowable, but were significantly higher than those of the other flowable RBCs. Clinical Significance: RBCs have undergone many modifications as they have evolved and represent the most relevant restorative materials in today’s dental practice. This study of low-shrinkage RBCs, conventional RBCs (non-flowable and flowable) and silorane-based composite – by in vitro evaluation of volumetric shrinkage, depth of cure and microhardness – reveals that although filler content is an important determinant of polymerization shrinkage, it is not the only variable that affects properties of materials that were tested in this study.