Color stability of nanocrystallite-treated and silicate-treated fillers of calcium phosphate composite resin: An in vitro study

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Some composite resins fail esthetically because the color differences to adjacent tooth structure are more than the limits of color tolerance (values are higher than 3.3 ΔE units). The purpose of this study was to assess the effect on color stability of surface-modified dicalcium phosphate anhydrous particles treated with nanocrystallites and silane coupling agents used as fillers for dental composite resin. Specimens were divided into 4 groups of fillers on unmodified (without modification) and on modified surfaces (silanization, nanocrystallites, and nanocrystallites with silica). These groups served as reinforcements and had 2 mass ratios of fillers (filler+resin) at 30% and 50%. The color differences were measured from day 1 after thermocycling procedures and for different specimen-treated procedures (drying, immersion, and thermocycling) at 1 to 16 days after 24 hours of immersion (n=5). ANOVA test was used to analyze the differences. The Student t test was used to evaluate the significant group comparisons, and a 3-way ANOVA was used to determine differences and interactions with the filler amount data (α=.05). Specimens with lower amounts of silica-treated fillers exhibited more variations in color than specimens with larger amounts of fillers. The main color variation was observed within the dried specimens after 24 hours of immersion. The color difference stabilized within 8 days. Fewer changes in the ΔE values were noted in the groups of filler surfaces with nanocrystallites than in groups without nanocrystallized treatment after the 1 day to 16 days of aging. Color difference was significantly reduced when the fillers reached a certain proportion, which further indicated that fillers with nanocrystal treatment could stabilize color variations within perceptible color tolerances (2.0 ΔE units) after immersion and thermocycling.