2023 Volume 66 Issue 5 Pages 263-270
Purpose: Bulk-fill resin composite (bulk-fill resin) permits better light transmittance than conventional light-cured resin composite and can be polymerized even in deep dental cavities that are difficult to reach using light irradiation. Resin composite loses its mechanical properties due to water sorption and becomes discolored over time. However, there are few reports on the water sorption and discoloration of bulk-fill resins. In this study, the effect of water sorption on the discoloration of commercially available bulk-fill resins of different compositions was evaluated.
Methods: Four bulk-fill resins were tested: GRACEFIL Bulk Flo (GC), Sonic Fill 2 (Kerr, USA), Tetric N-Ceram Bulk Fill (Ivoclar Vivadent, Liechtenstein), and BEAUTIFIL Bulk Flow (Shofu). Each was filled into stainless steel molds (diameter, 15.0 mm; thickness, 1.0 mm), polymerized using light irradiation from opposite sides for 90 s each, then polished with waterproof sandpaper (#1000 grit) and kept in water at 37℃ for 24 h. Water sorption of each specimen was measured following the standard JIS6514: 2013, dried using a desiccator, immersed in distilled water for 7 days, then weighed (n=5). The specimens were dried again, weighed, then the water sorption was calculated. The specimens were immersed in red wine for 7 days at 37℃, and their color tones before and after immersion were measured using a spectrophotometer (CM-3610d; Konica Minolta). The color changes due to discoloration of the bulk-fill resins were quantified using CIELab (ΔE＊ab) and CIEDE2000 (ΔE00) values (n=5) and compared using one-way ANOVA. Tukey’s multiple comparison test was used to determine significant differences between groups (α=0.05). Pearson’s product-moment correlation coefficient was used to analyze the correlation between water sorption and color difference of the bulk-fill resins.
Results: GRACEFIL Bulk Flo had significantly lower water sorption and color difference (ΔE＊ab, ΔE00) in comparison with the other bulk-fill resins, while the corresponding values for BEAUTIFIL Bulk Flow were significantly higher than the others. All bulk-fill resins had color differences that exceeded the value considered to be visually discernable (ΔE＊ab＞3.3, ΔE00＞2.3). Furthermore, a positive correlation was observed between water sorption and color difference (p＜0.001).
Conclusion: Water sorption and discoloration differ markedly among various bulk-fill resins. A strong positive correlation was measured between water sorption and discoloration. Water sorption of bulk-fill resin is an important factor affecting discoloration.
