Omeroglu, Merve KutukHekimoglu, Huseyin Can2025-05-312025-05-3120251472-683110.1186/s12903-025-05902-w2-s2.0-105003259126https://doi.org/10.1186/s12903-025-05902-whttps://hdl.handle.net/20.500.14517/7906Kutuk Omeroglu, Merve/0000-0002-0253-4212Background: The aim of this study is to investigate the colour stability, water absorption, and solubility values of low viscosity bulk fill resin composites that do not require an additional layer in comparison with high viscosity and low viscosity bulk fill resin composites used as a base. Methods: In the present study, four different bulk fill resin composites were used: Charisma Bulk Flow One (Kulzer), Estelite Bulk Fill Flowable (Tokuyama), X-tra Base (VOCO), Filtek One Bulk Fill (3M ESPE). The resin composites were prepared as disc-shaped samples with a diameter of 5 mm and a thickness of 4 mm, then polymerized using a LED light device (Elipar DeepCureS, 3M ESPE). The samples were kept in artificial saliva and coffee solution for 28 days to determine water absorption, solubility levels and triangle E values, with measurements taken on days 7, 14, 21 and 28. Water absorption and solubility levels were calculated based on ISO4049:2009 specification, and mean colour change values were calculated based on CIEDE2000 formula. Repeated Measures ANOVA, along with post hoc Bonferroni, Tamhane, and Adjusted Bonferroni tests, were used for the statistical evaluation of the data (p < 0.05). Results: Among all composite groups at all time intervals, Charisma Bulk Flow One composite showed the highest water absorption, solubility, and discolouration values. Conclusion: The water absorption, solubility and discolouration values of the resin composites used in this study were affected by the amount of filler in the resin structure. The clinical applicability of low-viscosity bulk-fill resin composites that do not require an additional capping layer should be carefully reassessed.eninfo:eu-repo/semantics/closedAccessDiscolourationLow Viscosity Bulk Fill CompositeSolubilityWater AbsorptionArticleQ2Q2251WOS:00147118850000340253330