Microstructural Properties and Surface Properties of a New Resin Composite Employing Structural Color Technology

In this study, we performed alkaline degradation testing to investigate the microstructural properties of a new resin composite composed of a single paste containing no pigments that still has the same basic structure as conventional pigment-containing composites. Our aim was to identify factors that affect the matching of various shades of teeth using structural color technology. The effect of these structural properties on the surface properties of the resin composite was also investigated. We found that the structural properties of the new composite included a wide distribution of many spherical organic fillers of various sizes. In addition, spherical inorganic filler of 260 nm in diameter was uniformly distributed at almost the same density both within the organic filler and within the base resin surrounding it. The organic filler and base resin, which are regarded as difficult to couple, were strongly bound without any gaps forming even after alkaline degradation testing. Although the surface layer of the organic filler was vulnerable to alkaline degradation, the center part exhibited very low degradation similar to the matrix surrounding the organic filler. In the new resin composite, the bonding state between the base resin and the various fillers was significantly improved. Furthermore, the microstructural properties were inferred to be effective factors for producing structural color, including the shape, particle diameter, distribution mode and density of the fillers as well as the properties of the base resin. However, these structural properties were not found to affect surface properties such as the line roughness, surface roughness, gloss, discoloration, and wettability.