Characterization of universal chromatic resin-based composites in terms of cell toxicity and viscoelastic behavior

•Universal chromatic RBCs are based either on structural coloring or on pigments.•Structurally colored RBCs generally led to lower mechanical properties but a better ability to absorb shock.•The cytotoxicity was comparable for all examined materials.•Universal chromatic RBCs can be classified in the regular RBCs class. A current trend to simplify dental restorative procedures is toward using universal chromatic light-cured resin-based composites (RBCs) designed to adapt esthetically to various clinical situations. This study offers a comparative characterization of the mechanical and cytotoxic behavior of such materials that use different techniques to adjust their optical properties (e.g., structural color instead of pigment addition), have different filler systems but are based on a comparable organic matrix. The structural appearance of the filler systems was assessed by scanning electron microscopy. Various quasi-static and viscoelastic parameters were evaluated at clinically relevant frequencies (0.5–5 Hz) using an instrumented indentation test with a Dynamic Mechanical Analysis (DMA) module. Cytotoxicity on human gingival fibroblasts (HGF-1), when exposed to eluates from tested RBCs specimens (up to one month), was assessed using a WST-1 colorimetric proliferation assay. Multifactor analysis of variance was applied to compare the parameters of interest (Martens, Vickers, and indentation hardness; elastic and total indentation work; creep, indentation depth; storage, loss, and indentation moduli; loss factor; cell viability) between analyzed RBCs, loading frequencies, and eluate age. Structural particularities of the filler systems are directly reflected in the mechanical behavior of the analyzed materials. Changes in the filler system, necessary to achieve structural color, generally resulted in lower mechanical properties but a better ability to absorb shock. In contrast, the cytotoxicity was comparable. Based on the performed characterization, universal chromatic RBCs fits in the conventional RBCs class to expect comparable clinical behavior.