Novel Dental Nanocomposites with Low-Shrinkage-Stress, Ion Recharge, Antibacterial and Remineralization Capabilities to Protect Tooth Structures

Abstract

The objectives of this dissertation were to: (1) investigate a bioactive nanocomposite with strong antibacterial and ion-recharge capabilities containing dimethylaminododecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP), and evaluate long-term Ca and P ion recharge by testing for 12 cycles of recharge and release; (2) develop a low-shrinkage-stress (LSS) nanocomposite with antibacterial and remineralization capabilities through the incorporation of DMAHDM and NACP to reduce marginal enamel and dentin demineralization under recurrent caries biofilm-model; (3) investigate the effects of the new composite on biofilm inhibition, mechanical properties, shrinkage stress, degree of conversion, and Ca and P ion releases; and (4) investigate the cytotoxicity of the new LSS composite and its monomers in vitro. For the antibacterial and rechargeable nanocomposite, biofilm lactic acid and colony-forming units (CFU) were measured. Ion recharge was tested for 12 cycles. For the LSS antibacterial and remineralizing nanocomposite, mechanical properties, shrinkage stress, and degree of conversion were evaluated. The growth of Streptococcus mutans and multi-species salivary biofilms was assessed using biofilm CFU, lactic acid production, and confocal laser scanning microscopy. Ca and P ion releases, and human gingival fibroblasts cytotoxicity were measured. The bioactive rechargeable nanocomposite reduced biofilm acid production and viability. High levels of ion releases were maintained throughout 12 cycles of recharge, maintaining steady-state releases without reduction in 6 months, representing long-term remineralization potential. The LSS composite with DMAHDM and NACP had flexural strength matching that of a commercial control composite. The bioactive low-shrinkage-stress composite substantially reduced the biofilm CFU and lactic acid production compared to control composite. The bioactive LSS composite exhibited no significant difference in antibacterial performance before and after three months of aging, demonstrating long-term antibacterial activity. The shrinkage stress of the bioactive low-shrinkage-stress nanocomposite was 36% lower than that of traditional control composite, with similar degrees of conversion. The new bioactive nanocomposite had a satisfactorily low cytotoxic effect toward human gingival fibroblasts and the new monomers had fibroblast viability similar to that of commercial control. The two developed nanocomposites are promising to inhibit recurrent caries and protect the teeth with an intended application for reducing recurrent caries.