Resin Composites Producing Structural Color Enhance Chameleon Effects

Objectives: Nano fillers with a diameter smaller than the wavelength of visible light produce structural color without the addition of any pigments. We conducted chromatic analysis of such nano fillers and reported their possibility to improve esthetic properties of resin composites. The aim of this study was to evaluate spectral reflection spectrums of resin composites incorporating nano fillers producing structural color.
Methods: Using commercial resin composites (Estelite Asteria, Tokuyama Dental), the disc specimens (Φ12×4.5 mm) having a cylindrical cavity (Φ4×2 mm) were prepared. For the base dentin part, resin composites with the shade of A1B, A2B, A3B, A3.5B, or A4B were used and that with the shade NE was layered on the top with 0.5 mm in thickness as enamel layer. Experimental resin composites incorporating uniform sized Φ150-nm/Φ260-nm spherical SiO₂-ZrO₂ supra-nano filler (D150RC/D260RC) were filled in the cavity using a bonding agent (BONDMER lightless, Tokuyama Dental) (n=10). Spectral reflection spectrums from 380 to 780 nm of each specimen were obtained by a spectral reflectometer using Φ3-mm fiber scope (ZE6000, Nippon Denshoku). As a control, Filtek Supreme Ultra (3M ESPE; FSU) were used (n=10).
Results: Spectral reflection spectrums of D150RC indicated a significant peak at 420 nm. Those of D260RC and FSU indicated a broad peak at 680 nm and 540 nm, respectively. The peaks, that is, the brightness and chromatic value for D150RC and D260RC significantly decreased according to the shift of shade from A1B to A4B of base resin composites (one-way ANOVA, Bonferroni test, p<0.05) while those peaks for FSU showed no significant difference (p>0.05).
Conclusions: Resin composites incorporating uniform sized Φ260-nm spherical SiO₂-ZrO₂ supra-nano filler, producing structural color, demonstrated a broad spectrum and the reduction in brightness and chromatic value by adapting to surrounding materials, suggesting its ability to enhance Chameleon effects to improve color matching.