Shades Match Using Layering Technique: A Spectrophotometric Analysis M. Anselmi*, R. Lorenzi, G. Dondi Dall’Orologio (Dept. Of Dental Materials And Operative Dentistry, University Of Bologna, Bologna, Italy) It has long been recognized that the color of tooth is strongly influenced by the color of dentin and the thickness of the enamel. The total color effect of natural teeth is a result of the combination of light reflected from the enamel surface and light scattered in the enamel and dentin and finally reflected back.   The dentin is the prime source of color and is modified by the translucency and thickness of enamel. Dentin shows lower value (L*), is more red (a*), yellow (b*) and opaque (T%) than enamel.   With composite resins the use of the recommended layering techniques has provided the means to produce a highly esthetic restoration, but has presented some problems to the area of color control.   The aim of this study was to use a spectrophotometric analysis to evaluate colorimetric data of two microhybrid composites Z 250 (3M) and Synergy (Coltene) and to select couples of shades with a color behavior similar to enamel and dentin. Samples of materials were prepared on the same resin tooth, were a cavity, 10mm in diameter, 3.0mm thick was done. A layer of glycerin was used on the cavity walls for an easier removal of the material. The cavity was filled with two layers and the composite cured for 40sec. with a visible light unit (XL 3000, 3M). A colorimetric analysis was performed by a reflection spectrophotometer (Pikkio, M.H.T.) with a 35°/0 type illuminating and viewing geometry, with a 2 mm measuring port and 1.5 mm detector area: the measure was automatically reported after three identical recordings. All the data were directly measured in CIELAB coordinates, with respect to standard light source A. The manufacturer states that the precision of the machine is within 1%.   For each couple of shades the first one represented the dentin and the second one the enamel. ΔL*, aΔ*, Δb* and ΔT% showed how much the second shade (enamel) had higher value, lower a* b* and more translucency than the first one (dentin).   Z 250 showed three possible couples (A4+I, B3+I, UD+B1) with ΔL* from 1.6 to 5.0; Δa*=0; Δb* from -0.6 to -9.0 and T% from 6 to 7. For other four couples of Z 250 (A3.5+A3, UD+B0.5, A4+A2, B3+A2) ΔL* varied from 1.8 to 5.7, Δa* from -3.0 to 0, Δb* from -9.0 to -1.5 but shades showed same translucency. Synergy showed eighteen possible couples (A3/D3compules+N, A3/D3c+P, A3.5/B3c+N, A3.5/B3c+P, A1/D2+N, A1/D2+P, C2/C3+N, C2/C3+P, A4/M5+N, A4/M5+P, A2/B2+N, A3.5/B3+A2/B2c, A3.5/B3+A3/D3, A3.5/D3+N, A3.5/D3+P, A3.5/D3+Transparent, A3/D3+N, A3/D3+P) with ΔL* from 0.3 to 9.7, Δa* from-0.5 to-5.8, Δb* from –3.3 to -13.8 and T% from 2 to 20. For other two couples of shades (C2/C3+A2/B2c,A3/D3+A3/D3c) ΔL* varied from 1.9 to 2.9, Δa* from-0.7 to -0.8, Db* from -1.7 to -3.2, but shades showed same translucency. Elaboration of spectrophotometric data made possible to select couples of shades with color behavior that can be used to simulate the layering effect of natural teeth.