Influence of Filler Distribution on the Color-Stability of Experimental Composite-Resins

Objectives: To determine the influence of the distribution of nano- and micro-sized fillers and thermocycling on the color, translucency and opalescence of experimental composite resins. Methods: A light curing resin matrix was made by 1:1 ratio mixing of BisGMA and TEGDMA. Silane coated nano- and micro-sized glass fillers with the mean particle size of 40nm and 0.77μm, respectively, were added in the ratios of 0:6 (N0M6), 1:5, 2:4, 3:3, 4:2, 5:1 and 6:0, with a total content of 60wt.% of the composite-resin. A commercial composite-resin with a filler content of 65wt.% was used as a reference. Reflected and transmitted colors of cured specimens (1mm in thickness) were measured with a spectrophotometer. Afterward, thermocycling was performed for 5000 times and the colors were measured again. Translucency parameter (TP), opalescence parameter (OP) and color change (DE*_ab) after thermocycling were calculated. The influence of filler distribution and thermocycling on the optical properties were analyzed with two-way repeated measures ANOVA (p<0.05). Results: Color changes after thermocycling were influence by the filler distribution (p<0.05), and were in the range of 1.1-3.6DE*_ab units; only the N0M6 group showed perceptible color change (DE*_ab>2.6). TP and OP values were influenced by the filler distribution and thermocycling (p<0.05), and were in the range of 14.8 to 49.1 and 1.5 to 29.8, respectively, before thermocycling, which were changed to 14.7 to 44.7 and 0.8 to 27.9, respectively, after thermocycling. Conclusion: The stability of optical properties of composite-resins was influenced by the filler distribution; the composite-resins containing nano-sized fillers showed better stability in color, translucency and opalescence after thermocycling as compared to those only containing micro-sized fillers.