Purpose: To measure the translucency parameter of opaque-shade resin composites. The secondary purpose was to evaluate the ability of the materials to mask dark background color.
Methods: CIELAB coordinates (L*, a*, b*) of three resin composites: UniFil S (UF), Palfique Estelite (PE), and Filtek A110 (FA) were determined in two shades (Opaque A3 and A3) at 1 mm and 2 mm thickness on a white backing, a backing of material itself and a black backing using a colorimeter. From the L* a* b* of 2 mm thick specimens on the white and black backing, translucency parameter (TP) were calculated for each material and shade to evaluate opacity of the materials. In addition, CIELAB color differences (deltaE*) were also calculated from the L*, a*, b* of 1 mm and 2 mm thick specimens on the material itself and on black backing, in order to estimate effectiveness of the resin composite materials to mask dark background color. If the calculated deltaE* were above 2, color differences were estimated as "perceptible."
Results: The TP values of Opaque A3 shade resins were lower than those of A3 resins for all the materials evaluated. When comparing the materials used, the Opaque A3 shade of FA indicates a higher TP value than those indicated for the Opaque A3 shade of the other two materials, while the A3 shade of FA revealed a higher TP value than the A3 shade of UF. As for the deltaE* values, the deltaE* recorded for 1 mm-thick specimens were in the range of "perceptible" and larger than those of 2 mm specimens, regardless of the shades and materials. For the 2 mm specimens, all of the deltaE* values for the Opaque A3 shade were classified as "imperceptible," whereas all deltaE* values for A3 shade were evaluated as "perceptible."
Clinical significance: The opaque-shade resin composites were less translucent than the usual composites. Hence, if a restoration was relatively thick, the opaque-shade resin composites might effectively mask the dark background color from the oral cavity. However, if a restoration was relatively thin, the opaque-shade resin composites could not mask the dark background color as well as the usual composites. Therefore, clinicians should take into consideration the effect of dark background color in the shade matching procedure for a relatively thin restoration, even if opaque-shade resin composite is used.