Engineering a Self‐Defensive Restoration‐Tooth Interface via Bioactive nMgO/E‐POSS Bulk‐Fill Resin Composites for Enhanced Dental Restorations

Light-curing resin composites (RCs) are widely used for tooth defect restoration. However, challenges such as high polymerization shrinkage and lack of anti-cariogenic activities compromise interfacial integrity and significantly increase restoration failure risks. To address these limitations, we developed a bioactive multifunctional bulk-fill RC by integrating sol-gel-synthesized monodisperse nano-MgO (nMgO), Stöber-derived monodisperse submicron spherical silica (sSiO₂), and dendritic epoxy-cyclohexyl functionalized polyhedral oligomeric silsesquioxane (E-POSS). RCs achieved a larger depth of cure (DOC > 4 mm) and higher degree of conversion (>80%), enabling reliable clinical handling. nMgO/E-POSS may synergistically enhance the restoration-tooth interface through: (1) low shrinkage and reduced shrinkage stress via E-POSS-mediated cationic ring-opening polymerization and rigid structure, effectively minimizing interfacial gaps and microleakage after 10,000 thermal cycles; (2) potent antibacterial activity against Streptococcus mutans through nMgO-mediated mechanisms including direct contact inhibition, Mg^2⁺/ROS generation, and alkaline microenvironment creation; and (3) E-POSS-guided biomimetic remineralization of demineralized dentin through Ca-P deposition and the stabilizing effect of Mg^2⁺ on amorphous calcium phosphate. Our novel RCs also maintain clinically satisfactory mechanical properties, hydrolytic/thermal stability, and excellent biosafety. By synergizing self-defensive antibacterial-remineralization capabilities with low-shrinkage-enhanced interfacial adaptation, this multifunctional composite provides a promising strategy for restoring large dental defects while preventing secondary caries and extending restoration longevity.