In vitro evaluation of physical properties, bond strength and bacterial adhesion to dentin of different self-adhesive composite resins

The aim of this study is to comparatively investigate the physical properties, bacterial adhesion, and dentin bonding strengths of different self-adhesive flowable composite resins and a conventional flowable composite resin. In this study, four different self-adhesive flowable composite resins were used: Vertise Flow (Group VF), Fusio Liquid Dentin (Group FL), Constic (Group Co), and Nova Compo SF (Group NC). Filtek Ultimate Flowable (Group FU) was selected as the conventional flowable composite resin. Disk-shaped samples were prepared, with 10 samples in each group, and polished with aluminum oxide particle polish discs. Measurements of surface microhardness (VHN), surface roughness (Ra), and color changes after 24 hours (∆E1) and 7 days (∆E2) in coffee solution were conducted, along with the examination of bacterial adhesion properties on the samples. The shear bond strength test was preferred to measure the bond strength (MPa) of the composite samples to dentin. A total of 60 teeth were used, with 12 samples in each group. The crown portion was partially removed to expose the dentin surface, which was then polished. Composite resins were applied to the dentin surface using a mold in accordance with the manufacturers' instructions. The bonding strength of the samples to dentin was measured by applying force until fracture occurred between the composite and dentin. Fracture types were then identified using a stereomicroscope. The composite-dentin interface of two samples from each group was examined with FE-SEM. Normality analysis was performed using the Shapiro Wilks test, and homogeneity of variance was assessed with the Levene test. The differences between groups were analyzed using one-way ANOVA, with Tukey's test used for pairwise comparisons. Significance was evaluated at p<0.05. In the microhardness analysis, Group FU exhibited the highest VHN value (55.54±3.93). Among the self-adhesive composite resins, Group Co showed the highest VHN value (42.25±4.65). No statistically significant difference was observed among the other self-adhesive composite resins in terms of VHN values (p>0.05). In the surface roughness analysis, the highest Ra value was observed in Group FL (0.375±0.068). Groups VF, Co, and NC showed similar Ra values (p>0.05). After 24 hours, Group FU had the lowest ∆E1 value (3.66±0.72), which was statistically similar to Groups Co and NC (p>0.05). Group FL had the highest ∆E1 value (11.46±1.68). Significant differences were found among all groups in ∆E2 values representing 7-day color changes (p<0.05). Group NC had the lowest ∆E2 value (4.06±0.9), while Group FL had the highest ∆E2 value (19.14±1.93). In bacterial adhesion experiments, Group FU showed the lowest S.mutans adhesion (0.098±0.007), while Group FL showed the highest S.mutans adhesion (0.215±0.008). The lowest L.casei adhesion was found in Group FU (0.101±0.011), and the highest in Group FL (0.218±0.006). Groups FL, Co, and NC most effectively inhibited S.mutans growth (p<0.05), while Group VF showed the least inhibition (p>0.05). No statistically significant difference was observed among the groups in inhibiting L.casei growth (p>0.05). In shear bond strength to dentin, Group FU exhibited the highest MPa value (14.04±7.02), while the lowest MPa values were observed in Groups VF and FL (4.30±1.50 and 5.60±6.95, respectively). In FE-SEM analysis, a continuous hybrid layer and regular resin tags were observed only in Group FU. Short resin tags were observed only in Group NC. In conclusion, although the microhardness values of self-adhesive composite resins are lower than those of conventional composite resins, the roughness values of all groups are similar. Additionally, no significant differences were observed between the groups when color change, bacterial adhesion, and bond strengths were examined. When the surface roughness, color change, and bacterial adhesion values of self-adhesive composite resins were compared, Nova Compo SF was found to be the most successful self-adhesive composite resin. Additionally, a hybrid layer formation, followed by short resin tags, was observed at the composite-dentin interface in this group, differing from other self-adhesive composite resins. Keywords: Self adhesive, flowable composite, microhardness, surface roughness, color change, bacterial adhesion.