Assessment of Color Stability of Various Flowable Composite Resins with Different Viscosities

Biomimetic restorative dentistry aims to preserve tooth structure and achieve optimal aesthetic harmony with surrounding dentition. The principles and protocols associated with biomimetic restorative dentistry are designed to enhance the longevity of the restoration. The use of flowable CRs is increasingly common; however, the effect of viscosity on the discoloration has not been clearly established. This in vitro study aimed to assess the color stability of flowable CRs with varying viscosities following immersion in common staining solutions and subsequent repolishing. A total of 250 disc-shaped specimens (8 mm × 2 mm) were prepared from five CRs with different viscosity profiles: high-viscosity (Spectra STHV, Dentsply, Milford, DE, USA), medium-viscosity (Estelite Universal Flow Medium, Tokuyama Dental Co., Tokyo, Japan), bulk-fill (Estelite Bulk-Fill Flow, Tokuyama Dental Co., Tokyo, Japan; SDR Plus, Dentsply, Milford, DE, USA), and packable (Estelite Posterior, Tokuyama Dental Co., Tokyo, Japan). After polymerization and baseline color measurements, specimens were immersed in coffee, tea, cola, red wine, or distilled water for 144 h. Color values were recorded before and after staining, and again following repolishing. Color changes (ΔE₁, ΔE₂, ΔE₃) were calculated using the CIE Lab system and statistically analyzed via two-way ANOVA and Tukey HSD (α = 0.05). Both the CR type and the staining solution substantially affected the color change. SDR Plus exhibited the highest ΔE values. Red wine caused the most discoloration. Repolishing enhanced color in selected groups.