Chitosan-arginine/amorphous calcium phosphate nanoparticles-containing orthodontic cement: antibacterial and remineralization strategies against enamel white spot lesions

During fixed orthodontic treatment, white spot lesions (WSLs) are prevalent issues associated with cariogenic bacteria. This study aimed to develop a novel orthodontic cement by incorporating a chitosan-arginine (Ch-Arg) complex and nanoparticles of amorphous calcium phosphate (NACP) into resin-modified glass ionomer cement (RMGIC), and to evaluate its antibacterial and remineralization effects for combating WSLs. Ch-Arg complex was synthesized via grafting and characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance analysis. RMGIC were modified with 5 wt% NACP, 1 wt% Ch-Arg, 2 wt% Ch-Arg, 1 wt% Ch-Arg + 5 wt% NACP, 2 wt% Ch-Arg + 5 wt% NACP, and no additions were control. Curing and bonding properties were assessed with degree of conversion (DC) and shear bond strength (SBS). The release of Ca2+, PO43−, and F− were determined, and pH measurements were recorded via submerging each specimen in lactic acid solution. The remineralization effect was confirmed by enamel microhardness test. Antimicrobial activity was evaluated with Streptococcus mutans, and cytocompatibility was tested with cytotoxicity test in vitro. Data were evaluated by one-way analysis of variance, followed by the Tukey honestly significant difference post hoc test, with a significance level set at 0.05. The 2 wt%Ch-Arg + 5 wt%NACP group showed a lower SBS value (p < 0.05), but remained within clinically acceptable threshold. For ion release, NACP addition increased Ca2+ and PO43− release, while the incorporation of either NACP or Ch-Arg did not impede sustained F− release. The NACP-containing groups showed increasing pH values and Vickers hardness at cariogenic pH levels, demonstrating acid-neutralization and remineralization property. Colony-forming unit counting and live/dead assay indicated that 2 wt%Ch-Arg + 5 wt%NACP group showed significant effect on microbial/antibiofilm growth (p < 0.05). The cell counting kit-8 test indicated no cytotoxicity, with statistically significant differences (p < 0.05). RMGIC containing 5 wt% NACP and 2 wt% Ch-Arg exhibited optimal antimicrobial efficacy, acid-neutralization capacity, and remineralization potential, while preserving clinically acceptable bonding and curing performance. The incorporation of Ch-Arg and NACP into RMGIC demonstrated adequate mechanical strength, enhanced antibacterial and remineralization effects, and favorable cytocompatibility. This combination offers a promising strategy to address WSLs in fixed orthodontics.