In vitro evaluation of physical properties and bacterial adhesion of different self-adhesive flowable composite...

The aim of this in vitro study was to comparatively evaluate the mechanical, optical, and biological properties of different self-adhesive flowable composite resins in comparison with a conventional flowable composite resin, with particular emphasis on the potential influence between material composition and bacterial adhesion.

Five flowable composite resins were investigated: Vertise Flow (VF), Fusio Liquid Dentin (FL), Constic (Co), Nova Compo SF (NC), and a conventional flowable composite, Filtek Ultimate Flowable (FU) (n = 10). Surface microhardness (VHN), surface roughness (Ra), and color changes after 24 h (ΔE₁) and 7 days (ΔE₂) of immersion in coffee solution were evaluated. Bacterial adhesion and growth inhibition of Streptococcus mutans and Lactobacillus casei were assessed using a crystal violet assay, supported by scanning electron microscopy (SEM). Data were analyzed using one-way ANOVA and Tukey's post hoc test (α = 0.05).

The conventional flowable composite (FU) exhibited the highest microhardness values (p < 0.05). Surface roughness differed significantly among the self-adhesive materials, with FL presenting the highest Ra values (p < 0.05). Color stability varied depending on material composition, with NC demonstrating the lowest ΔE values after prolonged staining (p < 0.05). Bacterial adhesion was material-dependent; FU and NC showed the lowest adhesion for both bacterial species, whereas FL exhibited the highest bacterial affinity (p < 0.05). Bacterial adhesion patterns could not be explained by surface roughness alone.

Self-adhesive flowable composite resins exhibited distinct mechanical, optical, and microbiological behaviors compared to a conventional flowable composite. The findings suggest that resin matrix chemistry and filler composition may influence bacterial adhesion beyond surface roughness, providing material-science-oriented insights relevant to the development and clinical selection of restorative materials. From a clinical perspective, materials with higher microhardness may be preferred for stress-bearing posterior restorations, whereas materials with lower bacterial adhesion may be advantageous for patients with high caries risk. In addition, color stability should be considered when selecting materials for anterior restorations where esthetic outcomes are critical.

The results of this study provide clinically relevant information for the selection of flowable composite resins by demonstrating differences in mechanical properties, color stability, and bacterial adhesion. While conventional flowable composites showed superior microhardness, certain self-adhesive composites exhibited comparable surface roughness, favorable color stability, and reduced bacterial adhesion, which may contribute to favorable esthetic performance and reduced bacterial accumulation.