Color Stability of Resin Composites Depends on The Filler and Chemical Surface Composition: an ex Vivo Study

Purpose: To investigate the cumulative effect of optical color dental resin composites and how this relates to bulk filler content and surface filler particle exposure and (changes) in the chemical composition of the composite surfaces. Methods: The 30 days oral exposure of dental composites, including wear and brushing with toothpaste, on optical color changes of two direct (Beautifil II, Filtek Z350 XT) and one indirect dental resin composite (Estenia C&B) was evaluated. The composites were inserted in an acrylic palatal appliance, and how this relates to bulk filler content, surface filler particle exposure, and (changes) in the chemical composition of the composite surfaces was investigated. Color values (ΔE) were evaluated according to the L, a, b, color coordinate system (International Commission on Illumination). Results: Significant discoloration occurred in all composites and was caused by a slightly darker, more reddish, and yellowish appearance of the composite that was in general not impacted by the absence or presence of brushing. The discoloration ΔE is related to bulk filler content, but not with filler particle exposure at the surface. Major increases in %N observed after intra-oral wear yield the conclusion that amines (i.e., photo-co-initiator) diffuse from the bulk to the composite surface to attract discolorants. In the absence of significant and systematic effects of brushing or not brushing, the causative discolorant is presumably the photoinitiator camphorquinone, known to produce a yellowish hue. Conclusions: Color stability of dental resin composites might be improved by changing the two-component photoinitiator/co-initiator system.