The color differences between different thicknesses of resin veneered over amalgam. 
Composites and compomers are popular in dental practice.  However, little is known about their esthetic appearance as veneering restorative materials over amalgam restorations.  This in vitro study was designed to assess the color differences of composite and compomer restorative materials, placed in thicknesses of 1 mm and 2 mm over amalgam.  Thirty six cylindrical Teflon molds were filled with amalgam (13 mm diameter, 2 mm thickness) and stored at 37 degrees C and 100% relative humidity for 7 days.  Nine veneers (for each thickness of 1 and 2 mm) were fabricated from four types of tooth-colored restorative material, Dyract AP (DYR), Compoglass F (COMP), Herculite XRV (XRV), and Vitalecense (VIT), over amalgam specimens using Teflon-split molds and following the manufacturers' instructions.  A spectrophotometer was used to measure the color difference DeltaE* between the two thicknesses.  Color difference DeltaE* values for 1 mm thickness veneers [XRV (2.52), Comp (5.46), VIT (6.73), and DYR (6.88)] were statistically significantly higher than the 2 mm thickness [XRV (1.32), Comp (3.24), VIT (4.89), and DYR (4.83)].  Although the XRV material had the lowest DeltaE* values, no statistically significant difference was found between the two thicknesses.  The color measurements at L*, a*, and b* showed most materials became darker in color at either thickness.  The thicker veneer specimens were found to be closer in color to the controls than the thinner specimens.  Only XRV had color differences (DeltaE*) small enough to be considered clinically acceptable (2.52 and 1.32 at 1 mm and 2 mm, respectively).  In this in vitro study the color of XRV was affected the least when veneered on amalgam.  Opaquers may be needed to be used with thinner veneers to minimize the effect of amalgam background.