Micro-CT assessment of remineralization by calcium, phosphate and fluoride agents

Methods: Human enamel specimens were immersed in a demineralizing solution (17.8 mM CaCl₂, 8.8 mM KH₂PO₄ and 100 mM lactic acid, pH 4.3) for 10 days to create enamel subsurface lesion artificially. Specimens were randomly divided into three groups and exposed to Ca, P and F containing agents (experimental material, Nippon Shika Yakuhin), 900 ppm F solution as NaF and deionized water (negative control). Micro-CT (Inspexio SMX-100CT, Shimadzu) scans of all specimens were taken before demineralization, after demineralization and remineralization. Specimens were then immersed in artificial saliva (1.5 mM CaCl₂, 0.9 mM KH₂PO₄, 130 mM KCl, and 20 mM HEPES, pH 7.0) for 10 days. Gray scale values were converted into mineral density values (g_HAp･cm^-3) using hydroxyapatite phantoms. Mineral density changes (comparing with baseline mineral density of sound enamel) were analyzed by a 3D structural analysis software (TRI/3D-BON, Ratoc System Engineering). Data were statistically analyzed by ANOVA. The microstructure of the crystals on the surface after treatments was analyzed by x-ray diffraction (XRD).

Results: Quantitative micro-CT assessment enabled nondestructive analysis of local changes in mineral density of enamel remineralization. Mineral density changes indicated higher mineral recovery with Ca, P and F containing agents compared to the 900 ppm F solution and negative control. In the Ca, P and F containing agents, there was no crystallization on the top surface as confirmed by XRD.

Conclusion: These in vitro results suggest that Ca, P and F containing agents have the potential to remineralize enamel subsurface lesion.

This study was supported by the G-COE Program at TMDU.