A nano-CaF₂-containing orthodontic cement with antibacterial and remineralization capabilities to combat enamel white spot lesions

Objectives: The objectives of this study were to develop a resin-modified glass ionomer containing nanoparticles of calcium fluoride (nCaF₂) and dimethylaminohexadecyl methacrylate (DMAHDM) for the first time and investigate the antibacterial and remineralization properties. Methods: nCaF₂ was synthesized using a spray-drying method and characterized using a transmission electron microscope. Twenty weight percentage (wt%) nCaF₂ and 3 wt% DMAHDM were incorporated into a RMGI (GC Ortho LC). Enamel shear bond strength (SBS) and cytotoxicity were determined. Fluoride (F) and calcium (Ca) ion releases were assessed. Biofilm live/dead staining, metabolic activity, polysaccharide and lactic production, and colony-forming units (CFU) were evaluated. The remineralization ability was determined by measuring the effects of cements on enamel surface hardness and lesion depth. Results: Incorporating 20 wt% nCaF₂ and 3 wt% DMAHDM did not compromise the SBS (p > 0.1). The decrease of pH from 7.0 to 4.0 significantly increased the F and Ca ion releases. The new cement greatly reduced the metabolic activity, polysaccharide and lactic acid productions, and lowered the biofilm CFU by 3 log, compared to commercial control (p < 0.05). The new cement increased the enamel hardness by 56% and decreased the lesion depth by 43%, compared to control (p < 0.05). The cell viability at 7 days against the new cement extracts was 82.2% of that of the negative control in culture medium without any extracts. Conclusions: The novel orthodontic cement containing nCaF₂ and DMAHDM achieved much stronger antibacterial and remineralization capabilities and greater enamel hardness than the commercial control did, without compromising the orthodontic bracket-enamel SBS and biocompatibility. Clinical Significance: The novel bioactive and nanostructured orthodontic cement is promising to inhibit enamel demineralization, white spot lesions and caries in orthodontic treatments.