The Synthesis Of NHA-CaCO₃ Composite And NFA-CaCO₃ Composite, And Their Effect On The Remineralization Of Enamel In Vitro

Objectives: To synthesize a composite of nano-hydroxyaptite and calcium carbonate (nHA-CaCO₃), and a composite of nano-fluoridated hydroxyaptite and calcium carbonate (nFA-CaCO₃). Investigate the effect of remineralization of early enamel caries with the two composites in vitro.Study 1. Materials and methods: Take the calcium carbonate (CaCO₃) as main material to synthesize nHA-CaCO₃ and nFA-CaCO₃. The properties of nHA-CaCO₃ and nFA-CaCO₃ were investigated through X-ray diffraction (XRD) and scanning electron miscroscope(SEM).Results: Both nHA-CaCO₃ and nFA-CaCO₃ were white and the pH of their solution was neutral. The XRD pattern confirmed that there were about 8?9% nHA/nFA in composites. The crystal size of hydroxyaptite in nHA-CaCO₃ was 16nm, while the crystal size of fluoridated hydroxyaptite in nFA-CaCO₃ was 28nm. SEM observation showed that nHA and nFA crystals were packaged on the surface of CaCO₃ crystals.Study 2. Materials and methods: Caries-like lesions were prepared in the enamel of extracted cattle incisors with demineralizing gel. The specimens were treated with 20%CaCO₃, 1000ppm Fluoride, 20%nHA-CaCO₃ and 20%nFA-CaCO₃. The SEM and XRD was used to investigated the change on the surface of enamel specimens. The effect of remineralization was assessed by the difference of enamel surface microhardness. The date were collected and analyzed with SNK test in ANOVA. Results: SEM observation showed that there is needl crystal on the specimens' surface in nHA-CaCO₃ and nFA-CaCO₃ groups. The XRD pattern confirmed that there were HA and FA on the specimens' surface in nFA-CaCO₃,nHA-CaCO₃ and fluoride groups, while there is CaCO₃ on the specimens' surface in nHA-CaCO₃ and CaCO₃ groups. The number of SMH and the percentage surface microhardness recovery shoed that nFA-CaCO₃,nHA-CaCO₃ and fluoride groups were significantly greater than CaCO₃ groups(P<0.05).Conclusions: The nHA-CaCO₃ and nFA-CaCO₃ had been successfully synthesized in this study. nHA-CaCO₃ and nFA-CaCO₃ has better effect to enhance remineralization of early enamel caries than CaCO₃, and nFA-CaCO₃ has better effect to deposit HA on the surface of enamel than nHA-CaCO₃.