Effect of Layer Thickness, Grain Size, and Surface Roughness on the Color Tone of High-Temperature Oxide Layer on CP Ti

Titanium dioxide (TiO2), widely used as a white pigment, exhibits high hiding power due to its high refractive index. In our research group, the optical characteristics of the oxide layer formed on titanium (Ti) and its alloys at high temperature have been investigated, aiming to enhance the esthetic properties of Ti-based dental materials. Although the refractive index is theoretically determined by the material’s dielectric constant and atomic volume, the visual appearance of oxide films can vary even among Ti alloys with identical compositions. These variations are influenced not only by changes in intrinsic refractive index due to alloying or impurities but also by the microstructural features of the oxide layer, such as layer thickness, particle size, and surface roughness, which affect light reflectance in the visible spectrum.