Diffuse and goniochromatic reflectance of translucent materials.

Abstract

Although the mechanical stability of dental restorations remains a priority, research is currently being pursued to improve the esthetics of restorations. This includes the technology of color matching and the general understanding of the appearance of natural teeth. Before the appearance of natural teeth can be mimicked, it must first be reduced to quantifiable parameters. Teeth and dental restorations typically have their appearance defined by their three-dimensional color, which then becomes the basis for appearance matching. However, standard color measurements cannot account for differences in translucency between materials, while a human observer readily can. Furthermore, teeth are translucent, multi-layered, biological composites that have aligned microstructures. These translucent layers and aligned microstructure make the color dependant upon the observation angle---a property known as goniochromism. This research shows how translucent materials exhibit significant goniochromatic behaviors. Since the translucency typically results in goniochromatic behavior, goniochromatic behavior is thought to be how translucency is perceived, and consequently, how color matching in translucent materials can potentially fail to match the appearance. To better understand the causes of goniochromism, fiber filler alignment, layering, and specularly reflecting backings were investigated as mechanisms of goniochromism. These same three mechanisms are also likely to affect the diffuse reflectance of translucent materials, which were also quantitatively studied. Another particularly odd property of human enamel is its ability to produce multiple-slit, Fraunhofer diffraction patterns, which this work reproduced using aligned, E-glass-fiber composites.