Water Sorption and Solubility in Bulk-fill Materials

Objectives: Water sorption and solubility are two factors related to different mechanical properties and biocompatibility of resin composites. The purpose of this study was to compare the degree of water sorption and solubility of bulk fill and nanohybrid flowable composites.
Methods: A total of 240 specimens (15 mm diameter; 1 mm depth) consisting of 4 bulk fill materials (SDR, Venus Bulk Fill, Filtek Bulk Fill and Sonic Fill) and 4 nanohybrid flowable composites (Premise Flowable, Filtek Supreme XT, Venus Diamond Flow, and Tetric EvoFlow) were prepared. The specimens were subdivided in 6 time groups (n=5): 1, 2, 3 and 4 weeks, 3 months and 6 months. Water sorption and solubility were tested according to ISO 4049:2009. Data were analysed using a Pearson’s correlation test, two-way ANOVA and Tukey post-hoc test.
Results: The Pearson correlation showed statistically significant differences for both groups of materials (p<0.001), but the correlation was positive for nanohybrid (r= 0.438) and negative for bulk fill materials (r= -0.289). The nanohybrid composites showed higher water sorption (WS= 24.52±5.17) and solubility (WL=2.31±2.99) than the bulk fill materials (WS=18.84±5.20; WL=2.13±2.93). The composite with the lowest water sorption was Sonic Fill (WS=12.53±3.16), and the highest was Tetric EvoFlow (WS=29.59±3.86). Regarding solubility, Venus Bulk Fill showed the lowest solubility (WL=0.22±2.69), and Sonic Fill showed the highest (WL=4.94±2.12). Both water sorption and solubility increased with time.
Conclusions: In spite of the fact that the relationship between water sorption and solubility was dependent on the composition of each individual material, the nanohybrid composites absorbed more water than did the bulk fill composites, although the nanohybrids were not the most soluble.