Novel rechargeable nano-CaF₂ orthodontic cement with high levels of long-term fluoride release

Objectives: Fluoride-containing orthodontic cements are used to combat white spot lesions (WSLs) in enamel. However, the fluoride (F) ion releases from these cements are relatively low and short-term. The objectives of this study were to develop a novel rechargeable orthodontic cement with nanoparticles of calcium fluoride (nCaF₂) to provide long-term and high levels of F release, and to investigate F recharge and physical and cytotoxic properties. Methods: The nCaF₂ with a mean particle size of 58 nm were synthesized using a spray-drying method. Pyromellitic glycerol dimethacrylate (PMGDM), ethoxylated bisphenol A dimethacrylate (EBPADMA), 2-hydroxyethyl methacrylate (HEMA) and bisphenol A glycidyl dimethacrylate (BisGMA) were used to prepare the cements (denoted PE and PEHB resins). A resin-modified glass ionomer (RMGI) served as control. Enamel shear bond strength (SBS), cytotoxicity, and F ion recharge and re-release were evaluated. Results: nCaF₂ cements had good SBS and excellent biocompatibility that were comparable to RMGI (p > 0.1). After a recharge for 1 min, the F re-release from PEHB + 30%nCaF₂ cement was 80% higher than RMGI (p < 0.05). Increasing nCaF₂ content from 20% to 30% greatly increased the F ion re-release (p < 0.05). The F ion re-release of nCaF₂ cements did not decrease with increasing the number of recharge and re-release cycles (p > 0.1). Conclusions: A novel F ion-rechargeable orthodontic cement containing nCaF₂ was developed with clinically acceptable enamel SBS, good biocompatibility, and sustained F ion recharge and re-release that were 1.8 folds that of a commercial RMGI. Clinical Significance: Novel rechargeable nCaF₂ orthodontic cement is promising to provide the needed long-term and high levels of F ion releases to inhibit WSLs in orthodontics.