Influence of thickness on color in multi-layering technique

Objectives: The aim of the study was to evaluate the influence of layer thickness on the final color for different shade and opacity composite combinations in a laboratory set-up simulating a 2-layer stratification technique. 

Methods: Resin disks of different thicknesses were made. From one composite system (Point4, Kerr Co.), four dentin shades were selected (A1, A2, A3, A4). For each shade, disks were produced of 0.5-3.0 mm thickness, with increasing thickness steps of 0.5 mm. Moreover, from the three translucent shades of the same system (T1, T2, T3) disks were made of 0.5-2.0 mm thickness, again with increasing thickness steps of 0.5 mm. For all 288 combinations of base + translucent material color was determined with a spectrophotometer. 

Results: For a mounting layer thickness from 0.5 to 3.0 mm of the base material, differences till to ΔE = 5.1 were recorded. These differences increased when the layer thickness of the translucent material decreased. The translucent shade also influence the final aspect of the samples, whereas each translucent shade acted differently dependent on their shade and their thickness. Their layer thickness played a significant role in color perception. 

Significance: Layer thickness and the proportion of thicknesses of the dentin and translucent shade greatly influence the final aspect of a multi-layer composite restoration. Good understanding of the optical behavior of each composite system is essential in order to obtain high quality in aesthetic dentistry.