Novel rechargeable calcium phosphate nanoparticle-containing orthodontic cement

White spot lesions (WSLs), due to enamel demineralization, occur frequently in orthodontic treatment. We recently developed a novel rechargeable dental composite containing nanoparticles of amorphous calcium phosphate (NACP) with long-term calcium (Ca) and phosphate (P) ion release and caries-inhibiting capability. The objectives of this study were to develop the first NACP-rechargeable orthodontic cement and investigate the effects of recharge duration and frequency on the efficacy of ion re-release. The rechargeable cement consisted of pyromellitic glycerol dimethacrylate (PMGDM) and ethoxylated bisphenol A dimethacrylate (EBPADMA). NACP was mixed into the resin at 40% by mass. Specimens were tested for orthodontic bracket shear bond strength (SBS) to enamel, Ca and P ion initial release, recharge and re-release. The new orthodontic cement exhibited an SBS similar to commercial orthodontic cement without CaP release (P>0.1). Specimens after one recharge treatment (e.g., 1 min immersion in recharge solution repeating three times in one day, referred to as “1 min 3 times”) exhibited a substantial and continuous re-release of Ca and P ions for 14 days without further recharge. The ion re-release did not decrease with increasing the number of recharge/re-release cycles (P>0.1). The ion re-release concentrations at 14 days versus various recharge treatments were as follows: 1 min 3 times>3 min 2 times>1 min 2 times>6 min 1 time>3 min 1 time>1 min 1 time. In conclusion, although previous studies have shown that NACP nanocomposite remineralized tooth lesions and inhibited caries, the present study developed the first orthodontic cement with Ca and P ion recharge and long-term release capability. This NACP-rechargeable orthodontic cement is a promising therapy to inhibit enamel demineralization and WSLs around orthodontic brackets. An orthodontic cement showing sustained release of calcium (Ca) and phosphate (P) ions may promote enamel remineralization. Fixed orthodontic attachments allow bacteria to accumulate causing enamel demineralization and white spot lesions. Dental cements formed from calcium phosphate (CaP) composites can release ions and prevent demineralization, however, these composites lack the required mechanical strength. Now, Hockin Xu at the University of Maryland, US, and colleagues report a nanoparticle-containing composite that shows sustained release of Ca/P ions over 14 days with an enamel bond strength similar to commercial orthodontic cements. The cement, formed from CaP nanoparticles mixed with a methacrylate-based resin, can be replenished with ions by placing it in Ca and P solutions, which may be possible using mouthwash. The CaP nanoparticle-based material was repeatedly re-charged with no observed decrease in ion release.