Color and opacity variations in three different resin-based composite products after water aging

Correct shade selection and clinical procedures may be invalidated as a result of intrinsic color shifting with time. The aim of this study was to test the influence of exposure to water on the color stability of three structurally different resin-based composites.

Six comparable Vita shades of three different resin-based composite systems were selected. For each product at each shade, three disks were made, 1 mm in thickness and 15 mm in diameter. The samples were studied with a spectrophotometer equipped with an integrating sphere. For color determinations, a 50% gray card was used as background, and the data were recorded in the CIE L*a*b* system. Opacity was calculated as the ratio of the reflectance of a specimen disk when backed by a black standard that when backed by a white standard. After the initial measurements, the samples were stored for 30 days in a 60 degrees C water bath and then measured again under the same conditions. The color shifts were calculated using the formula: delta E = [(L1 - L2)2 + (a1 - a2)2 + (b1 - b2)2]1/2.

If the standard of delta E < 3.3 as clinically acceptable was taken into consideration, one of the three materials involved in the study showed an unacceptable color shift for all shades. Only one of the three materials remained completely within an acceptable shade shift (delta E < 3.3) after aging. The difference in the color stability between products was significant (p < 0.001). The differences may be due to the different nature of the matrix and could also be correlated with filler particles dimensions. With reference to opacity; the results showed a similar pattern as that of the color and the statistical analysis also correlated.

From this work, it can be concluded that for some products, aging of composites in water leads to color instability and opacity variation.