Comparative Evaluation of Microbial Adhesion and Surface Morphology of Bonded and Non‐Bonded Resin‐Based Composite Materials: A SEM and Microbiological Study

Objective To evaluate the effect of applying bonding agents to uncured resin‐based composite surfaces on microbial adhesion and surface morphology. Materials and Methods Five resin‐based composite materials (Clearfil AP‐X Esthetics, Prime Dent, Beautifil II, Saremco microhybrid composite [MHC], and Saremco extra‐low shrinkage composite [ELS]) were evaluated under bonded (test) and non‐bonded (control) conditions ( n = 7 per group). In the bonded groups, a bonding agent was applied to the uncured composite surface prior to polymerization, whereas non‐bonded specimens were polymerized and subsequently polished. Streptococcus mutans adhesion was assessed using colony‐forming unit (CFU) analysis, and surface morphology was evaluated by scanning electron microscopy (SEM). Statistical analysis was performed using the Mann–Whitney U test ( α = 0.05). Results Bonded specimens exhibited significantly higher microbial adhesion than non‐bonded specimens for Saremco MHC, Saremco ELS, and Clearfil AP‐X Esthetics. In contrast, Prime‐Dent and Beautifil II showed lower CFU values in the bonded groups compared with the non‐bonded controls. Statistically significant differences between bonded and non‐bonded groups were observed for all tested composite materials (Mann–Whitney U test, p < 0.01). SEM analysis revealed increased surface irregularities, micro‐retentive features, and heterogeneous topography on bonded surfaces, whereas non‐bonded specimens exhibited comparatively smoother and more homogeneous surface morphologies. Conclusion Application of bonding agents to uncured composite resin surfaces alters surface morphology and is associated with altered microbial adhesion. These findings suggest that the clinical use of bonding agents as modeling liquids may influence the biological performance of composite restorations and should therefore be considered with caution.