Color matching ability of resin composites incorporating supra-nano spherical filler producing structural color.

Objective: The aim of this study was to evaluate the optical properties of supra-nano spherical fillers with different diameters and the color matching ability of resin composites (RC) incorporating these fillers.

Methods: Two types of SiO-ZrO nano fillers with different diameters (150nm and 260nm) were used. The size distribution of each filler was measured and filler morphology was observed. The colors and spectral reflection spectra were measured by a spectral reflectometer. Experimental RCs incorporating ϕ150-nm/ϕ260-nm filler (D150RC/D260RC) were prepared. For the base dentin part, disc specimens (Estelite Astelia: A1B, A2B, A3B, A3.5B, or A4B) were prepared with a cylindrical cavity. Estelite Astelia with NE shade was layered on top as the enamel layer. Disk specimens with different cavity depths were prepared using A3B shade. Experimental RC was used to fill the cavity, and spectral reflection spectrums were obtained and analyzed. Filtek Supreme Ultra (FSU) with A3B shade was used (n=10) as a control.

Results: Both ϕ150-nm and ϕ260-nm nano fillers showed uniform spherical shape and exhibited no aggregation. The maximum peaks of the spectral reflection spectra of the ϕ150-nm and ϕ260-nm nano fillers were 380nm and 580nm, producing structural colors close to blue and yellow, respectively. The spectral reflection spectrum of FSU had a broad peak at 540nm, and D150RC had a significant peak at 420nm. The D260RC specimen had a broad peak at 680nm. The peaks of D150RC and D260RC significantly decreased in accordance with the shift in base RC shade from A1B to A4B. There was no significant difference in the peak of the reflection spectral spectra among different cavity depths of D260RC. These results suggest that the experimental RC could reflect base RC colors via the matrix resin, and the amount of transmitted light from the base RC was not much different with cavity depth.

Significance: D260RC producing structural color demonstrated a broad spectrum and reduction in brightness and chromatic value by adapting to surrounding restorative materials, suggesting its ability to enhance the chameleon (blending) effects to improve color matching. D260RC showed better color matching ability than resin composite containing uniformly sized ϕ150-nm SiO-ZrO supra-nano spherical filler.