Cytotoxic Effects of Flowable Composite Resins with Different Resin Matrix Compositions on L929 Fibroblasts.

OBJECTIVE: To evaluate the cytotoxic effects of flowable composite resins with different resin matrix characteristics on L929 fibroblast cells. MATERIALS AND METHODS: Five flowable composite resins (GrandioSO Flow [GSF; VOCO Dental, Cuxhaven, Germany], EverX Flow [EXF; GC Europe, Leuven, Belgium], Admira Fusion Flow [AFF; VOCO Dental], Stark Bulk Fill Flow [SBFF; President Dental, Allershausen, Germany], and Estelite Bulk Fill Flow [EBFF; Tokuyama Dental, Tokyo, Japan]) were prepared as standardised discs (5 × 2 mm). Extracts obtained after 1 and 7 days of incubation were applied to L929 fibroblast cultures at different concentrations (direct, 1:2, 1:5, and 1:10 dilutions) for 24 and 48 hours. Cell viability was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide (MTT) assay. Data were analysed using a two-way analysis of variance (ANOVA) and Tukey post hoc test (α = 0.05). RESULTS: Direct exposure to all material extracts significantly reduced cell viability compared with the control group (P 0.0001). Cell viability increased with increasing dilution for all materials. EBFF and EXF consistently demonstrated the highest viability values and the most favourable biocompatibility profiles. In contrast, GSF exhibited the lowest cell viability values and the highest cytotoxic potential, particularly under direct exposure. AFF and SBFF showed intermediate responses. Overall, cell viability values were generally higher after 48 hours of exposure than after 24 hours. CONCLUSION: The cytotoxic effects of the flowable composite resins were concentration- and time-dependent. Although all tested materials generally maintained satisfactory cell viability under the evaluated conditions, significant differences were observed among the investigated materials. EBFF and EXF exhibited the most favourable biocompatibility, whereas GSF showed comparatively lower cell viability. Resin matrix characteristics, together with polymerisation-related factors, may influence the biological response of flowable composite resins.