Applications of photothermally mediated nanohybrids for white spot lesions in orthodontics

In orthodontic treatment, cariogenic bacteria in the oral cavity are the main cause of enamel white spot lesions (WSLs). Therefore, to effectively prevent and treat WSLs, it is crucial to inhibit the cariogenic bacterial activity while promoting the remineralization of demineralized tooth enamel. However, fluoride preparations commonly used for the prevention and treatment of WSLs can induce dental fluorosis if ingested in excess, and their remineralization effect is limited by the residual hydroxyapatite (HAp) content and salivary Ca2+ and PO43- levels. In this study, we propose a strategy (CMCS/ACP@PDA) for antibacterial and remineralization of WSLs by a nanohybrid of carboxymethyl chitosan (CMCS)-stabilized amorphous calcium phosphate (ACP) loaded polydopamine nanoparticles (PDA NPs) based on biomimetic remineralization techniques and biocompatible nearinfrared (NIR) photoactivation therapy. The nanohybrid utilizes the excellent photothermal conversion ability of polydopamine for antimicrobial purposes, while CMCS with its own positive and negative charges (-NH3+ and -COO-) acts as a biomimetic mineralizing agent to stabilize ACP, supplemented with abundant Ca2+ and PO4 3- for remineralization of demineralized enamel. The results showed that CMCS/ACP@PDA could effectively inhibit the adhesion of cariogenic Streptococcus mutants (S. mutants) with high bactericidal rates. In addition, the remineralization of demineralized enamel by nanohybrid was more effective after 7 days of in vitro mineralization. This study provides a theoretical and experimental basis for the use of CMCS/ACP@PDA nanohybrid materials as potential materials against WSLs.